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File: ssed.info, Node: Top, Next: Introduction, Up: (dir)
sed, a stream editor
********************
This file documents version 3.62 of `super-sed', a stream editor.
Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004 Free Software
Foundation, Inc.
This document is released under the terms of the GNU Free
Documentation License as published by the Free Software Foundation;
either version 1.1, or (at your option) any later version.
You should have received a copy of the GNU Free Documentation
License along with `super-sed'; see the file `COPYING.DOC'. If not,
write to the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
There are no Cover Texts and no Invariant Sections; this text, along
with its equivalent in the printed manual, constitutes the Title Page.
* Menu:
* Introduction:: Introduction
* Invoking sed:: Invocation
* sed Programs:: `sed' programs
* Examples:: Some sample scripts
* Limitations:: Limitations and (non-)limitations of `super-sed'
* Other Resources:: Other resources for learning about `sed'
* Reporting Bugs:: Reporting bugs
* Extended regexps:: `egrep'-style regular expressions
* Perl regexps:: Perl-style regular expressions
* Concept Index:: A menu with all the topics in this manual.
* Command and Option Index:: A menu with all `sed' commands and
command-line options.
--- The detailed node listing ---
sed Programs:
* Execution Cycle:: How `sed' works
* Addresses:: Selecting lines with `sed'
* Regular Expressions:: Overview of regular expression syntax
* Common Commands:: Often used commands
* The "s" Command:: `sed''s Swiss Army Knife
* Other Commands:: Less frequently used commands
* Programming Commands:: Commands for `sed' gurus
* Extended Commands:: Commands specific of `super-sed'
* Escapes:: Specifying special characters
Examples:
* Centering lines::
* Increment a number::
* Rename files to lower case::
* Print bash environment::
* Reverse chars of lines::
* tac:: Reverse lines of files
* cat -n:: Numbering lines
* cat -b:: Numbering non-blank lines
* wc -c:: Counting chars
* wc -w:: Counting words
* wc -l:: Counting lines
* head:: Printing the first lines
* tail:: Printing the last lines
* uniq:: Make duplicate lines unique
* uniq -d:: Print duplicated lines of input
* uniq -u:: Remove all duplicated lines
* cat -s:: Squeezing blank lines
Perl regexps:: Perl-style regular expressions
* Backslash:: Introduces special sequences
* Circumflex/dollar sign/period:: Behave specially with regard to new lines
* Square brackets:: Are a bit different in strange cases
* Options setting:: Toggle modifiers in the middle of a regexp
* Non-capturing subpatterns:: Are not counted when backreferencing
* Repetition:: Allows for non-greedy matching
* Backreferences:: Allows for more than 10 back references
* Assertions:: Allows for complex look ahead matches
* Non-backtracking subpatterns:: Often gives more performance
* Conditional subpatterns:: Allows if/then/else branches
* Recursive patterns:: For example to match parentheses
* Comments:: Because things can get complex...
File: ssed.info, Node: Introduction, Next: Invoking sed, Prev: Top, Up: Top
1 Introduction
**************
`sed' is a stream editor. A stream editor is used to perform basic text
transformations on an input stream (a file or input from a pipeline).
While in some ways similar to an editor which permits scripted edits
(such as `ed'), `sed' works by making only one pass over the input(s),
and is consequently more efficient. But it is `sed''s ability to
filter text in a pipeline which particularly distinguishes it from
other types of editors.
File: ssed.info, Node: Invoking sed, Next: sed Programs, Prev: Introduction, Up: Top
2 Invocation
************
Normally `sed' is invoked like this:
sed SCRIPT INPUTFILE...
The full format for invoking `sed' is:
sed OPTIONS... [SCRIPT] [INPUTFILE...]
If you do not specify INPUTFILE, or if INPUTFILE is `-', `sed'
filters the contents of the standard input. The SCRIPT is actually the
first non-option parameter, which `sed' specially considers a script
and not an input file if (and only if) none of the other OPTIONS
specifies a script to be executed, that is if neither of the `-e' and
`-f' options is specified.
`sed' may be invoked with the following command-line options:
`--version'
Print out the version of `sed' that is being run and a copyright
notice, then exit.
`--help'
Print a usage message briefly summarizing these command-line
options and the bug-reporting address, then exit.
`-n'
`--quiet'
`--silent'
By default, `sed' prints out the pattern space at the end of each
cycle through the script. These options disable this automatic
printing, and `sed' only produces output when explicitly told to
via the `p' command.
`-i[SUFFIX]'
`--in-place[=SUFFIX]'
This option specifies that files are to be edited in-place.
`super-sed' does this by creating a temporary file and sending
output to this file rather than to the standard output.(1).
This option implies `-s'.
When the end of the file is reached, the temporary file is renamed
to the output file's original name. The extension, if supplied,
is used to modify the name of the old file before renaming the
temporary file, thereby making a backup copy(2)).
This rule is followed: if the extension doesn't contain a `*',
then it is appended to the end of the current filename as a
suffix; if the extension does contain one or more `*' characters,
then _each_ asterisk is replaced with the current filename. This
allows you to add a prefix to the backup file, instead of (or in
addition to) a suffix, or even to place backup copies of the
original files into another directory (provided the directory
already exists).
If no extension is supplied, the original file is overwritten
without making a backup.
`-l N'
`--line-length=N'
Specify the default line-wrap length for the `l' command. A
length of 0 (zero) means to never wrap long lines. If not
specified, it is taken to be 70.
`--posix'
`super-sed' includes several extensions to POSIX sed. In order to
simplify writing portable scripts, this option disables all the
extensions that this manual documents, including additional
commands. Most of the extensions accept `sed' programs that are
outside the syntax mandated by POSIX, but some of them (such as
the behavior of the `N' command described in *note Reporting
Bugs::) actually violate the standard. If you want to disable
only the latter kind of extension, you can set the
`POSIXLY_CORRECT' variable to a non-empty value.
`-r'
`--regexp-extended'
Use extended regular expressions rather than basic regular
expressions. Extended regexps are those that `egrep' accepts;
they can be clearer because they usually have less backslashes,
but are a GNU extension and hence scripts that use them are not
portable. *Note Extended regular expressions: Extended regexps.
`-R'
`--regexp-perl'
Use Perl-style regular expressions rather than basic regular
expressions. Perl-style regexps are extremely powerful but are a
`super-sed' extension and hence scripts that use it are not
portable. *Note Perl-style regular expressions: Perl regexps.
`-s'
`--separate'
By default, `sed' will consider the files specified on the command
line as a single continuous long stream. This `super-sed'
extension allows the user to consider them as separate files:
range addresses (such as `/abc/,/def/') are not allowed to span
several files, line numbers are relative to the start of each
file, `$' refers to the last line of each file, and files invoked
from the `R' commands are rewound at the start of each file.
`-u'
`--unbuffered'
Buffer both input and output as minimally as practical. (This is
particularly useful if the input is coming from the likes of `tail
-f', and you wish to see the transformed output as soon as
possible.)
`-e SCRIPT'
`--expression=SCRIPT'
Add the commands in SCRIPT to the set of commands to be run while
processing the input.
`-f SCRIPT-FILE'
`--file=SCRIPT-FILE'
Add the commands contained in the file SCRIPT-FILE to the set of
commands to be run while processing the input.
If no `-e', `-f', `--expression', or `--file' options are given on
the command-line, then the first non-option argument on the command
line is taken to be the SCRIPT to be executed.
If any command-line parameters remain after processing the above,
these parameters are interpreted as the names of input files to be
processed. A file name of `-' refers to the standard input stream.
The standard input will be processed if no file names are specified.
---------- Footnotes ----------
(1) This applies to commands such as `=', `a', `c', `i', `l', `p'.
You can still write to the standard output by using the `w' or `W'
commands together with the `/dev/stdout' special file
(2) Note that `super-sed' creates the backup file whether or not
any output is actually changed.
File: ssed.info, Node: sed Programs, Next: Examples, Prev: Invoking sed, Up: Top
3 `sed' Programs
****************
A `sed' program consists of one or more `sed' commands, passed in by
one or more of the `-e', `-f', `--expression', and `--file' options, or
the first non-option argument if zero of these options are used. This
document will refer to "the" `sed' script; this is understood to mean
the in-order catenation of all of the SCRIPTs and SCRIPT-FILEs passed
in.
Each `sed' command consists of an optional address or address range,
followed by a one-character command name and any additional
command-specific code.
* Menu:
* Execution Cycle:: How `sed' works
* Addresses:: Selecting lines with `sed'
* Regular Expressions:: Overview of regular expression syntax
* Common Commands:: Often used commands
* The "s" Command:: `sed''s Swiss Army Knife
* Other Commands:: Less frequently used commands
* Programming Commands:: Commands for `sed' gurus
* Extended Commands:: Commands specific of `super-sed'
* Escapes:: Specifying special characters
File: ssed.info, Node: Execution Cycle, Next: Addresses, Up: sed Programs
3.1 How `sed' Works
===================
`sed' maintains two data buffers: the active _pattern_ space, and the
auxiliary _hold_ space. Both are initially empty.
`sed' operates by performing the following cycle on each lines of
input: first, `sed' reads one line from the input stream, removes any
trailing newline, and places it in the pattern space. Then commands
are executed; each command can have an address associated to it:
addresses are a kind of condition code, and a command is only executed
if the condition is verified before the command is to be executed.
When the end of the script is reached, unless the `-n' option is in
use, the contents of pattern space are printed out to the output
stream, adding back the trailing newline if it was removed.(1) Then the
next cycle starts for the next input line.
Unless special commands (like `D') are used, the pattern space is
deleted between two cycles. The hold space, on the other hand, keeps
its data between cycles (see commands `h', `H', `x', `g', `G' to move
data between both buffers).
---------- Footnotes ----------
(1) Actually, if `sed' prints a line without the terminating
newline, it will nevertheless print the missing newline as soon as
more text is sent to the same output stream, which gives the "least
expected surprise" even though it does not make commands like `sed -n
p' exactly identical to `cat'.
File: ssed.info, Node: Addresses, Next: Regular Expressions, Prev: Execution Cycle, Up: sed Programs
3.2 Selecting lines with `sed'
==============================
Addresses in a `sed' script can be in any of the following forms:
`NUMBER'
Specifying a line number will match only that line in the input.
(Note that `sed' counts lines continuously across all input files
unless `-i' or `-s' options are specified.)
`FIRST~STEP'
This GNU extension matches every STEPth line starting with line
FIRST. In particular, lines will be selected when there exists a
non-negative N such that the current line-number equals FIRST + (N
* STEP). Thus, to select the odd-numbered lines, one would use
`1~2'; to pick every third line starting with the second, `2~3'
would be used; to pick every fifth line starting with the tenth,
use `10~5'; and `50~0' is just an obscure way of saying `50'.
`$'
This address matches the last line of the last file of input, or
the last line of each file when the `-i' or `-s' options are
specified.
`/REGEXP/'
This will select any line which matches the regular expression
REGEXP. If REGEXP itself includes any `/' characters, each must
be escaped by a backslash (`\').
The empty regular expression `//' repeats the last regular
expression match (the same holds if the empty regular expression is
passed to the `s' command). Note that modifiers to regular
expressions are evaluated when the regular expression is compiled,
thus it is invalid to specify them together with the empty regular
expression.
`\%REGEXP%'
(The `%' may be replaced by any other single character.)
This also matches the regular expression REGEXP, but allows one to
use a different delimiter than `/'. This is particularly useful
if the REGEXP itself contains a lot of slashes, since it avoids
the tedious escaping of every `/'. If REGEXP itself includes any
delimiter characters, each must be escaped by a backslash (`\').
`/REGEXP/I'
`\%REGEXP%I'
The `I' modifier to regular-expression matching is a GNU extension
which causes the REGEXP to be matched in a case-insensitive manner.
`/REGEXP/M'
`\%REGEXP%M'
The `M' modifier to regular-expression matching is a `super-sed'
extension which causes `^' and `$' to match respectively (in
addition to the normal behavior) the empty string after a newline,
and the empty string before a newline. There are special character
sequences (`\A' and `\Z' in Perl mode, `\`' and `\'' in basic or
extended regular expression modes) which always match the
beginning or the end of the buffer. `M' stands for `multi-line'.
`/REGEXP/S'
`\%REGEXP%S'
The `S' modifier to regular-expression matching is only valid in
Perl mode and specifies that the dot character (`.') will match
the newline character too. `S' stands for `single-line'.
`/REGEXP/X'
`\%REGEXP%X'
The `X' modifier to regular-expression matching is also valid in
Perl mode only. If it is used, whitespace in the pattern (other
than in a character class) and characters between a `#' outside a
character class and the next newline character are ignored. An
escaping backslash can be used to include a whitespace or `#'
character as part of the pattern.
If no addresses are given, then all lines are matched; if one
address is given, then only lines matching that address are matched.
An address range can be specified by specifying two addresses
separated by a comma (`,'). An address range matches lines starting
from where the first address matches, and continues until the second
address matches (inclusively).
If the second address is a REGEXP, then checking for the ending
match will start with the line _following_ the line which matched the
first address: a range will always span at least two lines (except of
course if the input stream ends).
If the second address is a NUMBER less than (or equal to) the line
matching the first address, then only the one line is matched.
`super-sed' also supports some special two-address forms; all these
are GNU extensions:
`0,/REGEXP/'
A line number of `0' can be used in an address specification like
`0,/REGEXP/' so that `sed' will try to match REGEXP in the first
input line too. In other words, `0,/REGEXP/' is similar to
`1,/REGEXP/', except that if ADDR2 matches the very first line of
input the `0,/REGEXP/' form will consider it to end the range,
whereas the `1,/REGEXP/' form will match the beginning of its
range and hence make the range span up to the _second_ occurrence
of the regular expression.
Note that this is the only place where the `0' address makes
sense; there is no 0-th line and commands which are given the `0'
address in any other way will give an error.
`ADDR1,+N'
Matches ADDR1 and the N lines following ADDR1.
`ADDR1,~N'
Matches ADDR1 and the lines following ADDR1 until the next line
whose input line number is a multiple of N.
Appending the `!' character to the end of an address specification
negates the sense of the match. That is, if the `!' character follows
an address range, then only lines which do _not_ match the address range
will be selected. This also works for singleton addresses, and,
perhaps perversely, for the null address.
File: ssed.info, Node: Regular Expressions, Next: Common Commands, Prev: Addresses, Up: sed Programs
3.3 Overview of Regular Expression Syntax
=========================================
To know how to use `sed', people should understand regular expressions
("regexp" for short). A regular expression is a pattern that is
matched against a subject string from left to right. Most characters
are "ordinary": they stand for themselves in a pattern, and match the
corresponding characters in the subject. As a trivial example, the
pattern
The quick brown fox
matches a portion of a subject string that is identical to itself. The
power of regular expressions comes from the ability to include
alternatives and repetitions in the pattern. These are encoded in the
pattern by the use of "special characters", which do not stand for
themselves but instead are interpreted in some special way. Here is a
brief description of regular expression syntax as used in `sed'.
`CHAR'
A single ordinary character matches itself.
`*'
Matches a sequence of zero or more instances of matches for the
preceding regular expression, which must be an ordinary character,
a special character preceded by `\', a `.', a grouped regexp (see
below), or a bracket expression. As a GNU extension, a postfixed
regular expression can also be followed by `*'; for example, `a**'
is equivalent to `a*'. POSIX 1003.1-2001 says that `*' stands for
itself when it appears at the start of a regular expression or
subexpression, but many nonGNU implementations do not support this
and portable scripts should instead use `\*' in these contexts.
`\+'
As `*', but matches one or more. It is a GNU extension.
`\?'
As `*', but only matches zero or one. It is a GNU extension.
`\{I\}'
As `*', but matches exactly I sequences (I is a decimal integer;
for portability, keep it between 0 and 255 inclusive).
`\{I,J\}'
Matches between I and J, inclusive, sequences.
`\{I,\}'
Matches more than or equal to I sequences.
`\(REGEXP\)'
Groups the inner REGEXP as a whole, this is used to:
* Apply postfix operators, like `\(abcd\)*': this will search
for zero or more whole sequences of `abcd', while `abcd*'
would search for `abc' followed by zero or more occurrences
of `d'. Note that support for `\(abcd\)*' is required by
POSIX 1003.1-2001, but many non-GNU implementations do not
support it and hence it is not universally portable.
* Use back references (see below).
`.'
Matches any character, including newline.
`^'
Matches the null string at beginning of line, i.e. what appears
after the circumflex must appear at the beginning of line.
`^#include' will match only lines where `#include' is the first
thing on line--if there are spaces before, for example, the match
fails. `^' acts as a special character only at the beginning of
the regular expression or subexpression (that is, after `\(' or
`\|'). Portable scripts should avoid `^' at the beginning of a
subexpression, though, as POSIX allows implementations that treat
`^' as an ordinary character in that context.
`$'
It is the same as `^', but refers to end of line. `$' also acts
as a special character only at the end of the regular expression
or subexpression (that is, before `\)' or `\|'), and its use at
the end of a subexpression is not portable.
`[LIST]'
`[^LIST]'
Matches any single character in LIST: for example, `[aeiou]'
matches all vowels. A list may include sequences like
`CHAR1-CHAR2', which matches any character between (inclusive)
CHAR1 and CHAR2.
A leading `^' reverses the meaning of LIST, so that it matches any
single character _not_ in LIST. To include `]' in the list, make
it the first character (after the `^' if needed), to include `-'
in the list, make it the first or last; to include `^' put it
after the first character.
The characters `$', `*', `.', `[', and `\' are normally not
special within LIST. For example, `[\*]' matches either `\' or
`*', because the `\' is not special here. However, strings like
`[.ch.]', `[=a=]', and `[:space:]' are special within LIST and
represent collating symbols, equivalence classes, and character
classes, respectively, and `[' is therefore special within LIST
when it is followed by `.', `=', or `:'. Also, when not in
`POSIXLY_CORRECT' mode, special escapes like `\n' and `\t' are
recognized within LIST. *Note Escapes::.
`REGEXP1\|REGEXP2'
Matches either REGEXP1 or REGEXP2. Use parentheses to use complex
alternative regular expressions. The matching process tries each
alternative in turn, from left to right, and the first one that
succeeds is used. It is a GNU extension.
`REGEXP1REGEXP2'
Matches the concatenation of REGEXP1 and REGEXP2. Concatenation
binds more tightly than `\|', `^', and `$', but less tightly than
the other regular expression operators.
`\DIGIT'
Matches the DIGIT-th `\(...\)' parenthesized subexpression in the
regular expression. This is called a "back reference".
Subexpressions are implicity numbered by counting occurrences of
`\(' left-to-right.
`\n'
Matches the newline character.
`\CHAR'
Matches CHAR, where CHAR is one of `$', `*', `.', `[', `\', or `^'.
Note that the only C-like backslash sequences that you can
portably assume to be interpreted are `\n' and `\\'; in particular
`\t' is not portable, and matches a `t' under most implementations
of `sed', rather than a tab character.
Note that the regular expression matcher is greedy, i.e., matches
are attempted from left to right and, if two or more matches are
possible starting at the same character, it selects the longest.
Examples:
`abcdef'
Matches `abcdef'.
`a*b'
Matches zero or more `a's followed by a single `b'. For example,
`b' or `aaaaab'.
`a\?b'
Matches `b' or `ab'.
`a\+b\+'
Matches one or more `a's followed by one or more `b's: `ab' is the
shortest possible match, but other examples are `aaaab' or
`abbbbb' or `aaaaaabbbbbbb'.
`.*'
`.\+'
These two both match all the characters in a string; however, the
first matches every string (including the empty string), while the
second matches only strings containing at least one character.
`^main.*(.*)'
his matches a string starting with `main', followed by an opening
and closing parenthesis. The `n', `(' and `)' need not be
adjacent.
`^#'
This matches a string beginning with `#'.
`\\$'
This matches a string ending with a single backslash. The regexp
contains two backslashes for escaping.
`\$'
Instead, this matches a string consisting of a single dollar sign,
because it is escaped.
`[a-zA-Z0-9]'
In the C locale, this matches any ASCII letters or digits.
`[^ tab]\+'
(Here `tab' stands for a single tab character.) This matches a
string of one or more characters, none of which is a space or a
tab. Usually this means a word.
`^\(.*\)\n\1$'
This matches a string consisting of two equal substrings separated
by a newline.
`.\{9\}A$'
This matches nine characters followed by an `A'.
`^.\{15\}A'
This matches the start of a string that contains 16 characters,
the last of which is an `A'.
File: ssed.info, Node: Common Commands, Next: The "s" Command, Prev: Regular Expressions, Up: sed Programs
3.4 Often-Used Commands
=======================
If you use `sed' at all, you will quite likely want to know these
commands.
`#'
[No addresses allowed.]
The `#' character begins a comment; the comment continues until
the next newline.
If you are concerned about portability, be aware that some
implementations of `sed' (which are not POSIX conformant) may only
support a single one-line comment, and then only when the very
first character of the script is a `#'.
Warning: if the first two characters of the `sed' script are `#n',
then the `-n' (no-autoprint) option is forced. If you want to put
a comment in the first line of your script and that comment begins
with the letter `n' and you do not want this behavior, then be
sure to either use a capital `N', or place at least one space
before the `n'.
`q [EXIT-CODE]'
This command only accepts a single address.
Exit `sed' without processing any more commands or input. Note
that the current pattern space is printed if auto-print is not
disabled with the `-n' options. The ability to return an exit
code from the `sed' script is a `super-sed' extension.
`d'
Delete the pattern space; immediately start next cycle.
`p'
Print out the pattern space (to the standard output). This
command is usually only used in conjunction with the `-n'
command-line option.
`n'
If auto-print is not disabled, print the pattern space, then,
regardless, replace the pattern space with the next line of input.
If there is no more input then `sed' exits without processing any
more commands.
`{ COMMANDS }'
A group of commands may be enclosed between `{' and `}' characters.
This is particularly useful when you want a group of commands to
be triggered by a single address (or address-range) match.
File: ssed.info, Node: The "s" Command, Next: Other Commands, Prev: Common Commands, Up: sed Programs
3.5 The `s' Command
===================
The syntax of the `s' (as in substitute) command is
`s/REGEXP/REPLACEMENT/FLAGS'. The `/' characters may be uniformly
replaced by any other single character within any given `s' command.
The `/' character (or whatever other character is used in its stead)
can appear in the REGEXP or REPLACEMENT only if it is preceded by a `\'
character.
The `s' command is probably the most important in `sed' and has a
lot of different options. Its basic concept is simple: the `s' command
attempts to match the pattern space against the supplied REGEXP; if the
match is successful, then that portion of the pattern space which was
matched is replaced with REPLACEMENT.
The REPLACEMENT can contain `\N' (N being a number from 1 to 9,
inclusive) references, which refer to the portion of the match which is
contained between the Nth `\(' and its matching `\)'. Also, the
REPLACEMENT can contain unescaped `&' characters which reference the
whole matched portion of the pattern space. Finally, as a `super-sed'
extension, you can include a special sequence made of a backslash and
one of the letters `L', `l', `U', `u', or `E'. The meaning is as
follows:
`\L'
Turn the replacement to lowercase until a `\U' or `\E' is found,
`\l'
Turn the next character to lowercase,
`\U'
Turn the replacement to uppercase until a `\L' or `\E' is found,
`\u'
Turn the next character to uppercase,
`\E'
Stop case conversion started by `\L' or `\U'.
To include a literal `\', `&', or newline in the final replacement,
be sure to precede the desired `\', `&', or newline in the REPLACEMENT
with a `\'.
The `s' command can be followed by zero or more of the following
FLAGS:
`g'
Apply the replacement to _all_ matches to the REGEXP, not just the
first.
`NUMBER'
Only replace the NUMBERth match of the REGEXP.
Note: the POSIX standard does not specify what should happen when
you mix the `g' and NUMBER modifiers, and currently there is no
widely agreed upon meaning across `sed' implementations. For
`super-sed', the interaction is defined to be: ignore matches
before the NUMBERth, and then match and replace all matches from
the NUMBERth on.
`p'
If the substitution was made, then print the new pattern space.
Note: when both the `p' and `e' options are specified, the
relative ordering of the two produces very different results. In
general, `ep' (evaluate then print) is what you want, but
operating the other way round can be useful for debugging. For
this reason, the current version of `super-sed' interprets
specially the presence of `p' options both before and after `e',
printing the pattern space before and after evaluation, while in
general flags for the `s' command show their effect just once.
This behavior, although documented, might change in future
versions.
`w FILE-NAME'
If the substitution was made, then write out the result to the
named file. As a `super-sed' extension, two special values of
FILE-NAME are supported: `/dev/stderr', which writes the result to
the standard error, and `/dev/stdout', which writes to the standard
output.(1)
`e'
This command allows one to pipe input from a shell command into
pattern space. If a substitution was made, the command that is
found in pattern space is executed and pattern space is replaced
with its output. A trailing newline is suppressed; results are
undefined if the command to be executed contains a NUL character.
This is a `super-sed' extension.
`I'
`i'
The `I' modifier to regular-expression matching is a GNU extension
which makes `sed' match REGEXP in a case-insensitive manner.
`M'
`m'
The `M' modifier to regular-expression matching is a `super-sed'
extension which causes `^' and `$' to match respectively (in
addition to the normal behavior) the empty string after a newline,
and the empty string before a newline. There are special character
sequences (`\A' and `\Z' in Perl mode, `\`' and `\'' in basic or
extended regular expression modes) which always match the
beginning or the end of the buffer. `M' stands for `multi-line'.
`S'
`s'
The `S' modifier to regular-expression matching is only valid in
Perl mode and specifies that the dot character (`.') will match
the newline character too. `S' stands for `single-line'.
`X'
`x'
The `X' modifier to regular-expression matching is also valid in
Perl mode only. If it is used, whitespace in the pattern (other
than in a character class) and characters between a `#' outside a
character class and the next newline character are ignored. An
escaping backslash can be used to include a whitespace or `#'
character as part of the pattern.
---------- Footnotes ----------
(1) This is equivalent to `p' unless the `-i' option is being used.
File: ssed.info, Node: Other Commands, Next: Programming Commands, Prev: The "s" Command, Up: sed Programs
3.6 Less Frequently-Used Commands
=================================
Though perhaps less frequently used than those in the previous section,
some very small yet useful `sed' scripts can be built with these
commands.
`y/SOURCE-CHARS/DEST-CHARS/'
(The `/' characters may be uniformly replaced by any other single
character within any given `y' command.)
Transliterate any characters in the pattern space which match any
of the SOURCE-CHARS with the corresponding character in DEST-CHARS.
Instances of the `/' (or whatever other character is used in its
stead), `\', or newlines can appear in the SOURCE-CHARS or
DEST-CHARS lists, provide that each instance is escaped by a `\'.
The SOURCE-CHARS and DEST-CHARS lists _must_ contain the same
number of characters (after de-escaping).
`a\'
`TEXT'
As a GNU extension, this command accepts two addresses.
Queue the lines of text which follow this command (each but the
last ending with a `\', which are removed from the output) to be
output at the end of the current cycle, or when the next input
line is read.
Escape sequences in TEXT are processed, so you should use `\\' in
TEXT to print a single backslash.
As a GNU extension, if between the `a' and the newline there is
other than a whitespace-`\' sequence, then the text of this line,
starting at the first non-whitespace character after the `a', is
taken as the first line of the TEXT block. (This enables a
simplification in scripting a one-line add.) This extension also
works with the `i' and `c' commands.
`i\'
`TEXT'
As a GNU extension, this command accepts two addresses.
Immediately output the lines of text which follow this command
(each but the last ending with a `\', which are removed from the
output).
`c\'
`TEXT'
Delete the lines matching the address or address-range, and output
the lines of text which follow this command (each but the last
ending with a `\', which are removed from the output) in place of
the last line (or in place of each line, if no addresses were
specified). A new cycle is started after this command is done,
since the pattern space will have been deleted.
`='
As a GNU extension, this command accepts two addresses.
Print out the current input line number (with a trailing newline).
`l N'
Print the pattern space in an unambiguous form: non-printable
characters (and the `\' character) are printed in C-style escaped
form; long lines are split, with a trailing `\' character to
indicate the split; the end of each line is marked with a `$'.
N specifies the desired line-wrap length; a length of 0 (zero)
means to never wrap long lines. If omitted, the default as
specified on the command line is used. The N parameter is a
`super-sed' extension.
`r FILENAME'
As a GNU extension, this command accepts two addresses.
Queue the contents of FILENAME to be read and inserted into the
output stream at the end of the current cycle, or when the next
input line is read. Note that if FILENAME cannot be read, it is
treated as if it were an empty file, without any error indication.
As a `super-sed' extension, the special value `/dev/stdin' is
supported for the file name, which reads the contents of the
standard input.
`w FILENAME'
Write the pattern space to FILENAME. As a `super-sed' extension,
two special values of FILE-NAME are supported: `/dev/stderr',
which writes the result to the standard error, and `/dev/stdout',
which writes to the standard output.(1)
The file will be created (or truncated) before the first input
line is read; all `w' commands (including instances of `w' flag on
successful `s' commands) which refer to the same FILENAME are
output without closing and reopening the file.
`D'
Delete text in the pattern space up to the first newline. If any
text is left, restart cycle with the resultant pattern space
(without reading a new line of input), otherwise start a normal
new cycle.
`N'
Add a newline to the pattern space, then append the next line of
input to the pattern space. If there is no more input then `sed'
exits without processing any more commands.
`P'
Print out the portion of the pattern space up to the first newline.
`h'
Replace the contents of the hold space with the contents of the
pattern space.
`H'
Append a newline to the contents of the hold space, and then
append the contents of the pattern space to that of the hold space.
`g'
Replace the contents of the pattern space with the contents of the
hold space.
`G'
Append a newline to the contents of the pattern space, and then
append the contents of the hold space to that of the pattern space.
`x'
Exchange the contents of the hold and pattern spaces.
---------- Footnotes ----------
(1) This is equivalent to `p' unless the `-i' option is being used.
File: ssed.info, Node: Programming Commands, Next: Extended Commands, Prev: Other Commands, Up: sed Programs
3.7 Commands for `sed' gurus
============================
In most cases, use of these commands indicates that you are probably
better off programming in something like `awk' or Perl. But
occasionally one is committed to sticking with `sed', and these
commands can enable one to write quite convoluted scripts.
`: LABEL'
[No addresses allowed.]
Specify the location of LABEL for branch commands. In all other
respects, a no-op.
`b LABEL'
Unconditionally branch to LABEL. The LABEL may be omitted, in
which case the next cycle is started.
`t LABEL'
Branch to LABEL only if there has been a successful `s'ubstitution
since the last input line was read or conditional branch was taken.
The LABEL may be omitted, in which case the next cycle is started.
File: ssed.info, Node: Extended Commands, Next: Escapes, Prev: Programming Commands, Up: sed Programs
3.8 Commands Specific to `super-sed'
====================================
These commands are specific to `super-sed', so you must use them with
care and only when you are sure that hindering portability is not evil.
They allow you to check for `super-sed' extensions or to do tasks that
are required quite often, yet are unsupported by standard `sed's.
`e [COMMAND]'
This command allows one to pipe input from a shell command into
pattern space. Without parameters, the `e' command executes the
command that is found in pattern space and replaces the pattern
space with the output; a trailing newline is suppressed.
If a parameter is specified, instead, the `e' command interprets
it as a command and sends its output to the output stream (like
`r' does). The command can run across multiple lines, all but the
last ending with a back-slash.
In both cases, the results are undefined if the command to be
executed contains a NUL character.
`L N'
This `super-sed' extension fills and joins lines in pattern space
to produce output lines of (at most) N characters, like `fmt'
does; if N is omitted, the default as specified on the command
line is used. This command is considered a failed experiment and
unless there is enough request (which seems unlikely) will be
removed in future versions.
`Q [EXIT-CODE]'
This command only accepts a single address.
This command is the same as `q', but will not print the contents
of pattern space. Like `q', it provides the ability to return an
exit code to the caller.
This command can be useful because the only alternative ways to
accomplish this apparently trivial function are to use the `-n'
option (which can unnecessarily complicate your script) or
resorting to the following snippet, which wastes time by reading
the whole file without any visible effect:
:eat
$d Quit silently on the last line
N Read another line, silently
g Overwrite pattern space each time to save memory
b eat
`R FILENAME'
Queue a line of FILENAME to be read and inserted into the output
stream at the end of the current cycle, or when the next input
line is read. Note that if FILENAME cannot be read, or if its end
is reached, no line is appended, without any error indication.
As with the `r' command, the special value `/dev/stdin' is
supported for the file name, which reads a line from the standard
input.
`T LABEL'
Branch to LABEL only if there have been no successful
`s'ubstitutions since the last input line was read or conditional
branch was taken. The LABEL may be omitted, in which case the next
cycle is started.
`v VERSION'
This command does nothing, but makes `sed' fail if `super-sed'
extensions are not supported, simply because other versions of
`sed' do not implement it. In addition, you can specify the
version of `sed' that your script requires, such as `4.0.5'. The
default is `4.0' because that is the first version that
implemented this command.
This command enables all ssed extensions even if `POSIXLY_CORRECT'
is set in the environment.
`W FILENAME'
Write to the given filename the portion of the pattern space up to
the first newline. Everything said under the `w' command about
file handling holds here too.
File: ssed.info, Node: Escapes, Prev: Extended Commands, Up: sed Programs
3.9 GNU Extensions for Escapes in Regular Expressions
=====================================================
Until this chapter, we have only encountered escapes of the form `\^',
which tell `sed' not to interpret the circumflex as a special
character, but rather to take it literally. For example, `\*' matches
a single asterisk rather than zero or more backslashes.
This chapter introduces another kind of escape(1)--that is, escapes
that are applied to a character or sequence of characters that
ordinarily are taken literally, and that `sed' replaces with a special
character. This provides a way of encoding non-printable characters in
patterns in a visible manner. There is no restriction on the
appearance of non-printing characters in a `sed' script but when a
script is being prepared in the shell or by text editing, it is usually
easier to use one of the following escape sequences than the binary
character it represents:
The list of these escapes is:
`\a'
Produces or matches a BEL character, that is an "alert" (ASCII 7).
`\f'
Produces or matches a form feed (ASCII 12).
`\n'
Produces or matches a newline (ASCII 10).
`\r'
Produces or matches a carriage return (ASCII 13).
`\t'
Produces or matches a horizontal tab (ASCII 9).
`\v'
Produces or matches a so called "vertical tab" (ASCII 11).
`\cX'
Produces or matches `CONTROL-X', where X is any character. The
precise effect of `\cX' is as follows: if X is a lower case
letter, it is converted to upper case. Then bit 6 of the
character (hex 40) is inverted. Thus `\cz' becomes hex 1A, but
`\c{' becomes hex 3B, while `\c;' becomes hex 7B.
`\dXXX'
Produces or matches a character whose decimal ASCII value is XXX.
`\oXXX'
`\XXX'
Produces or matches a character whose octal ASCII value is XXX.
The syntax without the `o' is active in Perl mode, while the one
with the `o' is active in the normal or extended POSIX regular
expression modes.
`\xXX'
Produces or matches a character whose hexadecimal ASCII value is
XX.
`\b' (backspace) was omitted because of the conflict with the
existing "word boundary" meaning.
Other escapes match a particular character class and are valid only
in regular expressions:
`\w'
Matches any "word" character. A "word" character is any letter or
digit or the underscore character.
`\W'
Matches any "non-word" character.
`\b'
Matches a word boundary; that is it matches if the character to
the left is a "word" character and the character to the right is a
"non-word" character, or vice-versa.
`\B'
Matches everywhere but on a word boundary; that is it matches if
the character to the left and the character to the right are
either both "word" characters or both "non-word" characters.
`\`'
Matches only at the start of pattern space. This is different
from `^' in multi-line mode.
`\''
Matches only at the end of pattern space. This is different from
`$' in multi-line mode.
`\G'
Match only at the start of pattern space or, when doing a global
substitution using the `s///g' command and option, at the
end-of-match position of the prior match. For example,
`s/\Ga/Z/g' will change an initial run of `a's to a run of `Z's
---------- Footnotes ----------
(1) All the escapes introduced here are GNU extensions, with the
exception of `\n'. In basic regular expression mode, setting
`POSIXLY_CORRECT' disables them inside bracket expressions.
File: ssed.info, Node: Examples, Next: Limitations, Prev: sed Programs, Up: Top
4 Some Sample Scripts
*********************
Here are some `sed' scripts to guide you in the art of mastering `sed'.
* Menu:
Some exotic examples:
* Centering lines::
* Increment a number::
* Rename files to lower case::
* Print bash environment::
* Reverse chars of lines::
Emulating standard utilities:
* tac:: Reverse lines of files
* cat -n:: Numbering lines
* cat -b:: Numbering non-blank lines
* wc -c:: Counting chars
* wc -w:: Counting words
* wc -l:: Counting lines
* head:: Printing the first lines
* tail:: Printing the last lines
* uniq:: Make duplicate lines unique
* uniq -d:: Print duplicated lines of input
* uniq -u:: Remove all duplicated lines
* cat -s:: Squeezing blank lines
File: ssed.info, Node: Centering lines, Next: Increment a number, Up: Examples
4.1 Centering Lines
===================
This script centers all lines of a file on a 80 columns width. To
change that width, the number in `\{...\}' must be replaced, and the
number of added spaces also must be changed.
Note how the buffer commands are used to separate parts in the
regular expressions to be matched--this is a common technique.
#!/usr/bin/sed -f
# Put 80 spaces in the buffer
1 {
x
s/^$/ /
s/^.*$/&&&&&&&&/
x
}
# del leading and trailing spaces
y/tab/ /
s/^ *//
s/ *$//
# add a newline and 80 spaces to end of line
G
# keep first 81 chars (80 + a newline)
s/^\(.\{81\}\).*$/\1/
# \2 matches half of the spaces, which are moved to the beginning
s/^\(.*\)\n\(.*\)\2/\2\1/
File: ssed.info, Node: Increment a number, Next: Rename files to lower case, Prev: Centering lines, Up: Examples
4.2 Increment a Number
======================
This script is one of a few that demonstrate how to do arithmetic in
`sed'. This is indeed possible,(1) but must be done manually.
To increment one number you just add 1 to last digit, replacing it
by the following digit. There is one exception: when the digit is a
nine the previous digits must be also incremented until you don't have
a nine.
This solution by Bruno Haible is very clever and smart because it
uses a single buffer; if you don't have this limitation, the algorithm
used in *Note Numbering lines: cat -n, is faster. It works by
replacing trailing nines with an underscore, then using multiple `s'
commands to increment the last digit, and then again substituting
underscores with zeros.
#!/usr/bin/sed -f
/[^0-9]/ d
# replace all leading 9s by _ (any other character except digits, could
# be used)
:d
s/9\(_*\)$/_\1/
td
# incr last digit only. The first line adds a most-significant
# digit of 1 if we have to add a digit.
#
# The `tn' commands are not necessary, but make the thing
# faster
s/^\(_*\)$/1\1/; tn
s/8\(_*\)$/9\1/; tn
s/7\(_*\)$/8\1/; tn
s/6\(_*\)$/7\1/; tn
s/5\(_*\)$/6\1/; tn
s/4\(_*\)$/5\1/; tn
s/3\(_*\)$/4\1/; tn
s/2\(_*\)$/3\1/; tn
s/1\(_*\)$/2\1/; tn
s/0\(_*\)$/1\1/; tn
:n
y/_/0/
---------- Footnotes ----------
(1) `sed' guru Greg Ubben wrote an implementation of the `dc' RPN
calculator! It is distributed together with sed.
File: ssed.info, Node: Rename files to lower case, Next: Print bash environment, Prev: Increment a number, Up: Examples
4.3 Rename Files to Lower Case
==============================
This is a pretty strange use of `sed'. We transform text, and
transform it to be shell commands, then just feed them to shell. Don't
worry, even worse hacks are done when using `sed'; I have seen a script
converting the output of `date' into a `bc' program!
The main body of this is the `sed' script, which remaps the name
from lower to upper (or vice-versa) and even checks out if the remapped
name is the same as the original name. Note how the script is
parameterized using shell variables and proper quoting.
#! /bin/sh
# rename files to lower/upper case...
#
# usage:
# move-to-lower *
# move-to-upper *
# or
# move-to-lower -R .
# move-to-upper -R .
#
help()
{
cat << eof
Usage: $0 [-n] [-r] [-h] files...
-n do nothing, only see what would be done
-R recursive (use find)
-h this message
files files to remap to lower case
Examples:
$0 -n * (see if everything is ok, then...)
$0 *
$0 -R .
eof
}
apply_cmd='sh'
finder='echo "$@" | tr " " "\n"'
files_only=
while :
do
case "$1" in
-n) apply_cmd='cat' ;;
-R) finder='find "$@" -type f';;
-h) help ; exit 1 ;;
*) break ;;
esac
shift
done
if [ -z "$1" ]; then
echo Usage: $0 [-h] [-n] [-r] files...
exit 1
fi
LOWER='abcdefghijklmnopqrstuvwxyz'
UPPER='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
case `basename $0` in
*upper*) TO=$UPPER; FROM=$LOWER ;;
*) FROM=$UPPER; TO=$LOWER ;;
esac
eval $finder | sed -n '
# remove all trailing slashes
s/\/*$//
# add ./ if there is no path, only a filename
/\//! s/^/.\//
# save path+filename
h
# remove path
s/.*\///
# do conversion only on filename
y/'$FROM'/'$TO'/
# now line contains original path+file, while
# hold space contains the new filename
x
# add converted file name to line, which now contains
# path/file-name\nconverted-file-name
G
# check if converted file name is equal to original file name,
# if it is, do not print nothing
/^.*\/\(.*\)\n\1/b
# now, transform path/fromfile\n, into
# mv path/fromfile path/tofile and print it
s/^\(.*\/\)\(.*\)\n\(.*\)$/mv \1\2 \1\3/p
' | $apply_cmd
File: ssed.info, Node: Print bash environment, Next: Reverse chars of lines, Prev: Rename files to lower case, Up: Examples
4.4 Print `bash' Environment
============================
This script strips the definition of the shell functions from the
output of the `set' Bourne-shell command.
#!/bin/sh
set | sed -n '
:x
# if no occurrence of "=()" print and load next line
/=()/! { p; b; }
/ () $/! { p; b; }
# possible start of functions section
# save the line in case this is a var like FOO="() "
h
# if the next line has a brace, we quit because
# nothing comes after functions
n
/^{/ q
# print the old line
x; p
# work on the new line now
x; bx
'
File: ssed.info, Node: Reverse chars of lines, Next: tac, Prev: Print bash environment, Up: Examples
4.5 Reverse Characters of Lines
===============================
This script can be used to reverse the position of characters in lines.
The technique moves two characters at a time, hence it is faster than
more intuitive implementations.
Note the `tx' command before the definition of the label. This is
often needed to reset the flag that is tested by the `t' command.
Imaginative readers will find uses for this script. An example is
reversing the output of `banner'.(1)
#!/usr/bin/sed -f
/../! b
# Reverse a line. Begin embedding the line between two newlines
s/^.*$/\
&\
/
# Move first character at the end. The regexp matches until
# there are zero or one characters between the markers
tx
:x
s/\(\n.\)\(.*\)\(.\n\)/\3\2\1/
tx
# Remove the newline markers
s/\n//g
---------- Footnotes ----------
(1) This requires another script to pad the output of banner; for
example
#! /bin/sh
banner -w $1 $2 $3 $4 |
sed -e :a -e '/^.\{0,'$1'\}$/ { s/$/ /; ba; }' |
~/sedscripts/reverseline.sed
File: ssed.info, Node: tac, Next: cat -n, Prev: Reverse chars of lines, Up: Examples
4.6 Reverse Lines of Files
==========================
This one begins a series of totally useless (yet interesting) scripts
emulating various Unix commands. This, in particular, is a `tac'
workalike.
Note that on implementations other than GNU `sed' and `super-sed'
this script might easily overflow internal buffers.
#!/usr/bin/sed -nf
# reverse all lines of input, i.e. first line became last, ...
# from the second line, the buffer (which contains all previous lines)
# is *appended* to current line, so, the order will be reversed
1! G
# on the last line we're done -- print everything
$ p
# store everything on the buffer again
h
File: ssed.info, Node: cat -n, Next: cat -b, Prev: tac, Up: Examples
4.7 Numbering Lines
===================
This script replaces `cat -n'; in fact it formats its output exactly
like GNU `cat' does.
Of course this is completely useless and for two reasons: first,
because somebody else did it in C, second, because the following
Bourne-shell script could be used for the same purpose and would be
much faster:
#! /bin/sh
sed -e "=" $@ | sed -e '
s/^/ /
N
s/^ *\(......\)\n/\1 /
'
It uses `sed' to print the line number, then groups lines two by two
using `N'. Of course, this script does not teach as much as the one
presented below.
The algorithm used for incrementing uses both buffers, so the line
is printed as soon as possible and then discarded. The number is split
so that changing digits go in a buffer and unchanged ones go in the
other; the changed digits are modified in a single step (using a `y'
command). The line number for the next line is then composed and
stored in the hold space, to be used in the next iteration.
#!/usr/bin/sed -nf
# Prime the pump on the first line
x
/^$/ s/^.*$/1/
# Add the correct line number before the pattern
G
h
# Format it and print it
s/^/ /
s/^ *\(......\)\n/\1 /p
# Get the line number from hold space; add a zero
# if we're going to add a digit on the next line
g
s/\n.*$//
/^9*$/ s/^/0/
# separate changing/unchanged digits with an x
s/.9*$/x&/
# keep changing digits in hold space
h
s/^.*x//
y/0123456789/1234567890/
x
# keep unchanged digits in pattern space
s/x.*$//
# compose the new number, remove the newline implicitly added by G
G
s/\n//
h
File: ssed.info, Node: cat -b, Next: wc -c, Prev: cat -n, Up: Examples
4.8 Numbering Non-blank Lines
=============================
Emulating `cat -b' is almost the same as `cat -n'--we only have to
select which lines are to be numbered and which are not.
The part that is common to this script and the previous one is not
commented to show how important it is to comment `sed' scripts
properly...
#!/usr/bin/sed -nf
/^$/ {
p
b
}
# Same as cat -n from now
x
/^$/ s/^.*$/1/
G
h
s/^/ /
s/^ *\(......\)\n/\1 /p
x
s/\n.*$//
/^9*$/ s/^/0/
s/.9*$/x&/
h
s/^.*x//
y/0123456789/1234567890/
x
s/x.*$//
G
s/\n//
h
File: ssed.info, Node: wc -c, Next: wc -w, Prev: cat -b, Up: Examples
4.9 Counting Characters
=======================
This script shows another way to do arithmetic with `sed'. In this
case we have to add possibly large numbers, so implementing this by
successive increments would not be feasible (and possibly even more
complicated to contrive than this script).
The approach is to map numbers to letters, kind of an abacus
implemented with `sed'. `a's are units, `b's are tenths and so on: we
simply add the number of characters on the current line as units, and
then propagate the carry to tenths, hundredths, and so on.
As usual, running totals are kept in hold space.
On the last line, we convert the abacus form back to decimal. For
the sake of variety, this is done with a loop rather than with some 80
`s' commands(1): first we convert units, removing `a's from the number;
then we rotate letters so that tenths become `a's, and so on until no
more letters remain.
#!/usr/bin/sed -nf
# Add n+1 a's to hold space (+1 is for the newline)
s/./a/g
H
x
s/\n/a/
# Do the carry. The t's and b's are not necessary,
# but they do speed up the thing
t a
: a; s/aaaaaaaaaa/b/g; t b; b done
: b; s/bbbbbbbbbb/c/g; t c; b done
: c; s/cccccccccc/d/g; t d; b done
: d; s/dddddddddd/e/g; t e; b done
: e; s/eeeeeeeeee/f/g; t f; b done
: f; s/ffffffffff/g/g; t g; b done
: g; s/gggggggggg/h/g; t h; b done
: h; s/hhhhhhhhhh//g
: done
$! {
h
b
}
# On the last line, convert back to decimal
: loop
/a/! s/[b-h]*/&0/
s/aaaaaaaaa/9/
s/aaaaaaaa/8/
s/aaaaaaa/7/
s/aaaaaa/6/
s/aaaaa/5/
s/aaaa/4/
s/aaa/3/
s/aa/2/
s/a/1/
: next
y/bcdefgh/abcdefg/
/[a-h]/ b loop
p
---------- Footnotes ----------
(1) Some implementations have a limit of 199 commands per script
File: ssed.info, Node: wc -w, Next: wc -l, Prev: wc -c, Up: Examples
4.10 Counting Words
===================
This script is almost the same as the previous one, once each of the
words on the line is converted to a single `a' (in the previous script
each letter was changed to an `a').
It is interesting that real `wc' programs have optimized loops for
`wc -c', so they are much slower at counting words rather than
characters. This script's bottleneck, instead, is arithmetic, and
hence the word-counting one is faster (it has to manage smaller
numbers).
Again, the common parts are not commented to show the importance of
commenting `sed' scripts.
#!/usr/bin/sed -nf
# Convert words to a's
s/[ tab][ tab]*/ /g
s/^/ /
s/ [^ ][^ ]*/a /g
s/ //g
# Append them to hold space
H
x
s/\n//
# From here on it is the same as in wc -c.
/aaaaaaaaaa/! bx; s/aaaaaaaaaa/b/g
/bbbbbbbbbb/! bx; s/bbbbbbbbbb/c/g
/cccccccccc/! bx; s/cccccccccc/d/g
/dddddddddd/! bx; s/dddddddddd/e/g
/eeeeeeeeee/! bx; s/eeeeeeeeee/f/g
/ffffffffff/! bx; s/ffffffffff/g/g
/gggggggggg/! bx; s/gggggggggg/h/g
s/hhhhhhhhhh//g
:x
$! { h; b; }
:y
/a/! s/[b-h]*/&0/
s/aaaaaaaaa/9/
s/aaaaaaaa/8/
s/aaaaaaa/7/
s/aaaaaa/6/
s/aaaaa/5/
s/aaaa/4/
s/aaa/3/
s/aa/2/
s/a/1/
y/bcdefgh/abcdefg/
/[a-h]/ by
p
File: ssed.info, Node: wc -l, Next: head, Prev: wc -w, Up: Examples
4.11 Counting Lines
===================
No strange things are done now, because `sed' gives us `wc -l'
functionality for free!!! Look:
#!/usr/bin/sed -nf
$=
File: ssed.info, Node: head, Next: tail, Prev: wc -l, Up: Examples
4.12 Printing the First Lines
=============================
This script is probably the simplest useful `sed' script. It displays
the first 10 lines of input; the number of displayed lines is right
before the `q' command.
#!/usr/bin/sed -f
10q
File: ssed.info, Node: tail, Next: uniq, Prev: head, Up: Examples
4.13 Printing the Last Lines
============================
Printing the last N lines rather than the first is more complex but
indeed possible. N is encoded in the second line, before the bang
character.
This script is similar to the `tac' script in that it keeps the
final output in the hold space and prints it at the end:
#!/usr/bin/sed -nf
1! {; H; g; }
1,10 !s/[^\n]*\n//
$p
h
Mainly, the scripts keeps a window of 10 lines and slides it by
adding a line and deleting the oldest (the substitution command on the
second line works like a `D' command but does not restart the loop).
The "sliding window" technique is a very powerful way to write
efficient and complex `sed' scripts, because commands like `P' would
require a lot of work if implemented manually.
To introduce the technique, which is fully demonstrated in the rest
of this chapter and is based on the `N', `P' and `D' commands, here is
an implementation of `tail' using a simple "sliding window."
This looks complicated but in fact the working is the same as the
last script: after we have kicked in the appropriate number of lines,
however, we stop using the hold space to keep inter-line state, and
instead use `N' and `D' to slide pattern space by one line:
#!/usr/bin/sed -f
1h
2,10 {; H; g; }
$q
1,9d
N
D
File: ssed.info, Node: uniq, Next: uniq -d, Prev: tail, Up: Examples
4.14 Make Duplicate Lines Unique
================================
This is an example of the art of using the `N', `P' and `D' commands,
probably the most difficult to master.
#!/usr/bin/sed -f
h
:b
# On the last line, print and exit
$b
N
/^\(.*\)\n\1$/ {
# The two lines are identical. Undo the effect of
# the n command.
g
bb
}
# If the `N' command had added the last line, print and exit
$b
# The lines are different; print the first and go
# back working on the second.
P
D
As you can see, we mantain a 2-line window using `P' and `D'. This
technique is often used in advanced `sed' scripts.
File: ssed.info, Node: uniq -d, Next: uniq -u, Prev: uniq, Up: Examples
4.15 Print Duplicated Lines of Input
====================================
This script prints only duplicated lines, like `uniq -d'.
#!/usr/bin/sed -nf
$b
N
/^\(.*\)\n\1$/ {
# Print the first of the duplicated lines
s/.*\n//
p
# Loop until we get a different line
:b
$b
N
/^\(.*\)\n\1$/ {
s/.*\n//
bb
}
}
# The last line cannot be followed by duplicates
$b
# Found a different one. Leave it alone in the pattern space
# and go back to the top, hunting its duplicates
D
File: ssed.info, Node: uniq -u, Next: cat -s, Prev: uniq -d, Up: Examples
4.16 Remove All Duplicated Lines
================================
This script prints only unique lines, like `uniq -u'.
#!/usr/bin/sed -f
# Search for a duplicate line --- until that, print what you find.
$b
N
/^\(.*\)\n\1$/ ! {
P
D
}
:c
# Got two equal lines in pattern space. At the
# end of the file we simply exit
$d
# Else, we keep reading lines with `N' until we
# find a different one
s/.*\n//
N
/^\(.*\)\n\1$/ {
bc
}
# Remove the last instance of the duplicate line
# and go back to the top
D
File: ssed.info, Node: cat -s, Prev: uniq -u, Up: Examples
4.17 Squeezing Blank Lines
==========================
As a final example, here are three scripts, of increasing complexity
and speed, that implement the same function as `cat -s', that is
squeezing blank lines.
The first leaves a blank line at the beginning and end if there are
some already.
#!/usr/bin/sed -f
# on empty lines, join with next
# Note there is a star in the regexp
:x
/^\n*$/ {
N
bx
}
# now, squeeze all '\n', this can be also done by:
# s/^\(\n\)*/\1/
s/\n*/\
/
This one is a bit more complex and removes all empty lines at the
beginning. It does leave a single blank line at end if one was there.
#!/usr/bin/sed -f
# delete all leading empty lines
1,/^./{
/./!d
}
# on an empty line we remove it and all the following
# empty lines, but one
:x
/./!{
N
s/^\n$//
tx
}
This removes leading and trailing blank lines. It is also the
fastest. Note that loops are completely done with `n' and `b', without
exploting the fact that `sed' cycles back to the top of the script
automatically at the end of a line.
#!/usr/bin/sed -nf
# delete all (leading) blanks
/./!d
# get here: so there is a non empty
:x
# print it
p
# get next
n
# got chars? print it again, etc...
/./bx
# no, don't have chars: got an empty line
:z
# get next, if last line we finish here so no trailing
# empty lines are written
n
# also empty? then ignore it, and get next... this will
# remove ALL empty lines
/./!bz
# all empty lines were deleted/ignored, but we have a non empty. As
# what we want to do is to squeeze, insert a blank line artificially
i\
bx
File: ssed.info, Node: Limitations, Next: Other Resources, Prev: Examples, Up: Top
5 `super-sed''s Limitations and Non-limitations
***********************************************
For those who want to write portable `sed' scripts, be aware that some
implementations have been known to limit line lengths (for the pattern
and hold spaces) to be no more than 4000 bytes. The POSIX standard
specifies that conforming `sed' implementations shall support at least
8192 byte line lengths. `super-sed' has no built-in limit on line
length; as long as it can `malloc()' more (virtual) memory, you can
feed or construct lines as long as you like.
However, recursion is used to handle subpatterns and indefinite
repetition. This means that the available stack space may limit the
size of the buffer that can be processed by certain patterns.
There are some size limitations in the regular expression matcher
but it is hoped that they will never in practice be relevant. The
maximum length of a compiled pattern is 65539 (sic) bytes. All values
in repeating quantifiers must be less than 65536. The maximum nesting
depth of all parenthesized subpatterns, including capturing and
non-capturing subpatterns(1), assertions, and other types of
subpattern, is 200.
Also, `super-sed' recognizes the POSIX syntax `[.CH.]' and `[=CH=]'
where CH is a "collating element", but these are not supported, and an
error is given if they are encountered.
Here are a few distinctions between the real Perl-style regular
expressions and those that `-R' recognizes.
1. Lookahead assertions do not allow repeat quantifiers after them
Perl permits them, but they do not mean what you might think. For
example, `(?!a){3}' does not assert that the next three characters
are not `a'. It just asserts three times that the next character
is not `a' -- a waste of time and nothing else.
2. Capturing subpatterns that occur inside negative lookahead head
assertions are counted, but their entries are counted as
empty in the second half of an `s' command. Perl sets its
numerical variables from any such patterns that are matched before
the assertion fails to match something (thereby succeeding), but
only if the negative lookahead assertion contains just one branch.
3. The following Perl escape sequences are not supported: `\l', `\u',
`\L', `\U', `\E', `\Q'. In fact these are implemented by Perl's
general string-handling and are not part of its pattern matching
engine.
4. The Perl `\G' assertion is not supported as it is not relevant to
single pattern matches.
5. Fairly obviously, `super-sed' does not support the `(?{code})' and
`(?p{code})' constructions. However, there is some experimental
support for recursive patterns using the non-Perl item `(?R)'.
6. There are at the time of writing some oddities in Perl 5.005_02
concerned with the settings of captured strings when part of a
pattern is repeated. For example, matching `aba' against the
pattern `/^(a(b)?)+$/' sets `$2'(2) to the value `b', but matching
`aabbaa' against `/^(aa(bb)?)+$/' leaves `$2' unset. However, if
the pattern is changed to `/^(aa(b(b))?)+$/' then `$2' (and `$3')
are set. In Perl 5.004 `$2' is set in both cases, and that is also
true of `super-sed'.
7. Another as yet unresolved discrepancy is that in Perl 5.005_02 the
pattern `/^(a)?(?(1)a|b)+$/' matches the string `a', whereas in
`super-sed' it does not. However, in both Perl and `super-sed'
`/^(a)?a/' matched against `a' leaves $1 unset.
---------- Footnotes ----------
(1) The distinction is meaningful when referring to Perl-style
regular expressions.
(2) `$2' would be `\2' in `super-sed'.
File: ssed.info, Node: Other Resources, Next: Reporting Bugs, Prev: Limitations, Up: Top
6 Other Resources for Learning About `sed'
******************************************
In addition to several books that have been written about `sed' (either
specifically or as chapters in books which discuss shell programming),
one can find out more about `sed' (including suggestions of a few
books) from the FAQ for the `sed-users' mailing list, available from
any of:
`http://www.student.northpark.edu/pemente/sed/sedfaq.html'
`http://sed.sf.net/grabbag/tutorials/sedfaq.html'
Also of interest are
`http://www.student.northpark.edu/pemente/sed/index.htm' and
`http://sed.sf.net/grabbag', which include `sed' tutorials and other
`sed'-related goodies.
The `sed-users' mailing list itself maintained by Sven Guckes. To
subscribe, visit `http://groups.yahoo.com' and search for the
`sed-users' mailing list.
File: ssed.info, Node: Reporting Bugs, Next: Extended regexps, Prev: Other Resources, Up: Top
7 Reporting Bugs
****************
Email bug reports to <bonzini AT gnu.org>. Be sure to include the word
"sed" somewhere in the `Subject:' field. Also, please include the
output of `sed --version' in the body of your report if at all possible.
Please do not send a bug report like this:
while building frobme-1.3.4
$ configure
error--> sed: file sedscr line 1: Unknown option to 's'
If `super-sed' doesn't configure your favorite package, take a few
extra minutes to identify the specific problem and make a stand-alone
test case. Unlike other programs such as C compilers, making such test
cases for `sed' is quite simple.
A stand-alone test case includes all the data necessary to perform
the test, and the specific invocation of `sed' that causes the problem.
The smaller a stand-alone test case is, the better. A test case should
not involve something as far removed from `sed' as "try to configure
frobme-1.3.4". Yes, that is in principle enough information to look
for the bug, but that is not a very practical prospect.
Here are a few commonly reported bugs that are not bugs.
`N' command on the last line
Most versions of `sed' exit without printing anything when the `N'
command is issued on the last line of a file. `super-sed' prints
pattern space before exiting unless of course the `-n' command
switch has been specified. This choice is by design.
For example, the behavior of
sed N foo bar
would depend on whether foo has an even or an odd number of
lines(1). Or, when writing a script to read the next few lines
following a pattern match, traditional implementations of `sed'
would force you to write something like
/foo/{ $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N }
instead of just
/foo/{ N;N;N;N;N;N;N;N;N; }
In any case, the simplest workaround is to use `$d;N' in scripts
that rely on the traditional behavior, or to set the
`POSIXLY_CORRECT' variable to a non-empty value.
Regex syntax clashes (problems with backslashes)
`sed' uses the POSIX basic regular expression syntax. According to
the standard, the meaning of some escape sequences is undefined in
this syntax; notable in the case of `sed' are `\|', `\+', `\?',
`\`', `\'', `\<', `\>', `\b', `\B', `\w', and `\W'.
As in all GNU programs that use POSIX basic regular expressions,
`sed' interprets these escape sequences as special characters.
So, `x\+' matches one or more occurrences of `x'. `abc\|def'
matches either `abc' or `def'.
This syntax may cause problems when running scripts written for
other `sed's. Some `sed' programs have been written with the
assumption that `\|' and `\+' match the literal characters `|' and
`+'. Such scripts must be modified by removing the spurious
backslashes if they are to be used with modern implementations of
`sed', like `super-sed' or GNU `sed'.
On the other hand, some scripts use s|abc\|def||g to remove
occurrences of _either_ `abc' or `def'. While this worked until
`sed' 4.0.x, newer versions interpret this as removing the string
`abc|def'. This is again undefined behavior according to POSIX,
and this interpretation is arguably more robust: older `sed's, for
example, required that the regex matcher parsed `\/' as `/' in the
common case of escaping a slash, which is again undefined
behavior; the new behavior avoids this, and this is good because
the regex matcher is only partially under our control.
In addition, this version of `sed' supports several escape
characters (some of which are multi-character) to insert
non-printable characters in scripts (`\a', `\c', `\d', `\o', `\r',
`\t', `\v', `\x'). These can cause similar problems with scripts
written for other `sed's.
`-i' clobbers read-only files
In short, `sed -i' will let you delete the contents of a read-only
file, and in general the `-i' option (*note Invocation: Invoking
sed.) lets you clobber protected files. This is not a bug, but
rather a consequence of how the Unix filesystem works.
The permissions on a file say what can happen to the data in that
file, while the permissions on a directory say what can happen to
the list of files in that directory. `sed -i' will not ever open
for writing a file that is already on disk. Rather, it will work
on a temporary file that is finally renamed to the original name:
if you rename or delete files, you're actually modifying the
contents of the directory, so the operation depends on the
permissions of the directory, not of the file. For this same
reason, `sed' does not let you use `-i' on a writeable file in a
read-only directory (but unbelievably nobody reports that as a
bug...).
`0a' does not work (gives an error)
There is no line 0. 0 is a special address that is only used to
treat addresses like `0,/RE/' as active when the script starts: if
you write `1,/abc/d' and the first line includes the word `abc',
then that match would be ignored because address ranges must span
at least two lines (barring the end of the file); but what you
probably wanted is to delete every line up to the first one
including `abc', and this is obtained with `0,/abc/d'.
---------- Footnotes ----------
(1) which is the actual "bug" that prompted the change in behavior
File: ssed.info, Node: Extended regexps, Next: Perl regexps, Prev: Reporting Bugs, Up: Top
Appendix A Extended regular expressions
***************************************
The only difference between basic and extended regular expressions is in
the behavior of a few characters: `?', `+', parentheses, and braces
(`{}'). While basic regular expressions require these to be escaped if
you want them to behave as special characters, when using extended
regular expressions you must escape them if you want them _to match a
literal character_.
Examples:
`abc?'
becomes `abc\?' when using extended regular expressions. It
matches the literal string `abc?'.
`c\+'
becomes `c+' when using extended regular expressions. It matches
one or more `c's.
`a\{3,\}'
becomes `a{3,}' when using extended regular expressions. It
matches three or more `a's.
`\(abc\)\{2,3\}'
becomes `(abc){2,3}' when using extended regular expressions. It
matches either `abcabc' or `abcabcabc'.
`\(abc*\)\1'
becomes `(abc*)\1' when using extended regular expressions.
Backreferences must still be escaped when using extended regular
expressions.
File: ssed.info, Node: Perl regexps, Next: Concept Index, Prev: Extended regexps, Up: Top
Appendix B Perl-style regular expressions
*****************************************
_This part is taken from the `pcre.txt' file distributed together with
the free PCRE regular expression matcher; it was written by Philip
Hazel._
Perl introduced several extensions to regular expressions, some of
them incompatible with the syntax of regular expressions accepted by
Emacs and other GNU tools (whose matcher was based on the Emacs
matcher). `super-sed' implements both kinds of extensions.
* Menu:
Other extensions can be roughly subdivided in two categories
On one hand Perl introduces several more escaped sequences
(that is, sequences introduced by a backslash). On the other
hand, it specifies that if a question mark follows an open
parentheses it should give a special meaning to the parenthesized
group.
* Backslash:: Introduces special sequences
* Circumflex/dollar sign/period:: Behave specially with regard to new lines
* Square brackets:: Are a bit different in strange cases
* Options setting:: Toggle modifiers in the middle of a regexp
* Non-capturing subpatterns:: Are not counted when backreferencing
* Repetition:: Allows for non-greedy matching
* Backreferences:: Allows for more than 10 back references
* Assertions:: Allows for complex look ahead matches
* Non-backtracking subpatterns:: Often gives more performance
* Conditional subpatterns:: Allows if/then/else branches
* Recursive patterns:: For example to match parentheses
* Comments:: Because things can get complex...
File: ssed.info, Node: Backslash, Next: Circumflex/dollar sign/period, Up: Perl regexps
B.1 Backslash
=============
There are a few difference in the handling of backslashed sequences in
Perl mode.
First of all, there are no `\o' and `\d' sequences. ASCII values
for characters can be specified in octal with a `\XXX' sequence, where
XXX is a sequence of up to three octal digits. If the first digit is a
zero, the treatment of the sequence is straightforward; just note that
if the character that follows the escaped digit is itself an octal
digit, you have to supply three octal digits for XXX. For example
`\07' is a BEL character rather than a NUL and a literal `7' (this
sequence is instead represented by `\0007').
The handling of a backslash followed by a digit other than 0 is
complicated. Outside a character class, `sed' reads it and any
following digits as a decimal number. If the number is less than 10, or
if there have been at least that many previous capturing left
parentheses in the expression, the entire sequence is taken as a back
reference. A description of how this works is given later, following
the discussion of parenthesized subpatterns.
Inside a character class, or if the decimal number is greater than 9
and there have not been that many capturing subpatterns, `sed' re-reads
up to three octal digits following the backslash, and generates a
single byte from the least significant 8 bits of the value. Any
subsequent digits stand for themselves. For example:
\040 is another way of writing a space
\40 is the same, provided there are fewer than 40
previous capturing subpatterns
\7 is always a back reference
\011 is always a tab
\11 might be a back reference, or another way of
writing a tab
\0113 is a tab followed by the character `3'
\113 is the character with octal code 113 (since there
can be no more than 99 back references)
\377 is a byte consisting entirely of 1 bits (ASCII 255)
\81 is either a back reference, or a binary zero
followed by the two characters `81'
Note that octal values of 100 or greater must not be introduced
duced by a leading zero, because no more than three octal digits are
ever read. Note that this applies only to the LHS pattern; it is not
possible yet to specify more than 9 backreferences on the RHS of the
`s' command.
All the sequences that define a single byte value can be used both
inside and outside character classes. In addition, inside a character
class, the sequence `\b' is interpreted as the backspace character (hex
08). Outside a character class it has a different meaning (see below).
In addition, there are four additional escapes specifying generic
character classes (like `\w' and `\W' do):
`\d'
Matches any decimal digit
`\D'
Matches any character that is not a decimal digit
In Perl mode, these character type sequences can appear both inside
and outside character classes. Instead, in POSIX mode these sequences
(as well as `\w' and `\W') are treated as two literal characters (a
backslash and a letter) inside square brackets.
Escaped sequences specifying assertions are also different in Perl
mode. An assertion specifies a condition that has to be met at a
particular point in a match, without consuming any characters from the
subject string. The use of subpatterns for more complicated assertions
is described below. The backslashed assertions are
`\b'
Asserts that the point is at a word boundary. A word boundary is
a position in the subject string where the current character and
the previous character do not both match `\w' or `\W' (i.e. one
matches `\w' and the other matches `\W'), or the start or end of
the string if the first or last character matches `\w',
respectively.
`\B'
Asserts that the point is not at a word boundary.
`\A'
Asserts the matcher is at the start of pattern space (independent
of multiline mode).
`\Z'
Asserts the matcher is at the end of pattern space, or at a
newline before the end of pattern space (independent of multiline
mode)
`\z'
Asserts the matcher is at the end of pattern space (independent of
multiline mode)
These assertions may not appear in character classes (but note that
`\b' has a different meaning, namely the backspace character, inside a
character class). Note that Perl mode does not support directly
assertions for the beginning and the end of word; the GNU extensions
`\<' and `\>' achieve this purpose in POSIX mode instead.
The `\A', `\Z', and `\z' assertions differ from the traditional
circumflex and dollar sign (described below) in that they only ever
match at the very start and end of the subject string, whatever options
are set; in particular `\A' and `\z' are the same as the GNU extensions
`\`' and `\'' that are active in POSIX mode.
File: ssed.info, Node: Circumflex/dollar sign/period, Next: Square brackets, Prev: Backslash, Up: Perl regexps
B.2 Circumflex, dollar sign, period
===================================
Outside a character class, in the default matching mode, the circumflex
character is an assertion which is true only if the current matching
point is at the start of the subject string. Inside a character class,
the circumflex has an entirely different meaning (see below).
The circumflex need not be the first character of the pattern if a
number of alternatives are involved, but it should be the first thing
in each alternative in which it appears if the pattern is ever to match
that branch. If all possible alternatives, start with a circumflex,
that is, if the pattern is constrained to match only at the start of
the subject, it is said to be an "anchored" pattern. (There are also
other constructs structs that can cause a pattern to be anchored.)
A dollar sign is an assertion which is true only if the current
matching point is at the end of the subject string, or immediately
before a newline character that is the last character in the string (by
default). A dollar sign need not be the last character of the pattern
if a number of alternatives are involved, but it should be the last
item in any branch in which it appears. A dollar sign has no special
meaning in a character class.
The meanings of the circumflex and dollar sign characters are
changed if the `M' modifier option is used. When this is the case, they
match immediately after and immediately before an internal `\n'
character, respectively, in addition to matching at the start and end
of the subject string. For example, the pattern `/^abc$/' matches the
subject string `def\nabc' in multiline mode, but not otherwise.
Consequently, patterns that are anchored in single line mode because
all branches start with `^' are not anchored in multiline mode.
Note that the sequences `\A', `\Z', and `\z' can be used to match
the start and end of the subject in both modes, and if all branches of
a pattern start with `\A' is it always anchored, whether the `M'
modifier is set or not.
Outside a character class, a dot in the pattern matches any one
character in the subject, including a non-printing character, but not
(by default) newline. If the `S' modifier is used, dots match newlines
as well. Actually, the handling of dot is entirely independent of the
handling of circumflex and dollar sign, the only relationship being
that they both involve newline characters. Dot has no special meaning
in a character class.
File: ssed.info, Node: Square brackets, Next: Options setting, Prev: Circumflex/dollar sign/period, Up: Perl regexps
B.3 Square brackets
===================
An opening square bracket introduces a character class, terminated by a
closing square bracket. A closing square bracket on its own is not
special. If a closing square bracket is required as a member of the
class, it should be the first data character in the class (after an
initial circumflex, if present) or escaped with a backslash.
A character class matches a single character in the subject; the
character must be in the set of characters defined by the class, unless
the first character in the class is a circumflex, in which case the
subject character must not be in the set defined by the class. If a
circumflex is actually required as a member of the class, ensure it is
not the first character, or escape it with a backslash.
For example, the character class [aeiou] matches any lower case
vowel, while [^aeiou] matches any character that is not a lower case
vowel. Note that a circumflex is just a convenient venient notation for
specifying the characters which are in the class by enumerating those
that are not. It is not an assertion: it still consumes a character
from the subject string, and fails if the current pointer is at the end
of the string.
When caseless matching is set, any letters in a class represent both
their upper case and lower case versions, so for example, a caseless
`[aeiou]' matches uppercase and lowercase `A's, and a caseless
`[^aeiou]' does not match `A', whereas a case-sensitive version would.
The newline character is never treated in any special way in
character classes, whatever the setting of the `S' and `M' options
(modifiers) is. A class such as `[^a]' will always match a newline.
The minus (hyphen) character can be used to specify a range of
characters in a character class. For example, `[d-m]' matches any
letter between d and m, inclusive. If a minus character is required in
a class, it must be escaped with a backslash or appear in a position
where it cannot be interpreted as indicating a range, typically as the
first or last character in the class.
It is not possible to have the literal character `]' as the end
character of a range. A pattern such as `[W-]46]' is interpreted as a
class of two characters (`W' and `-') followed by a literal string
`46]', so it would match `W46]' or `-46]'. However, if the `]' is
escaped with a backslash it is interpreted as the end of range, so
`[W-\]46]' is interpreted as a single class containing a range followed
by two separate characters. The octal or hexadecimal representation of
`]' can also be used to end a range.
Ranges operate in ASCII collating sequence. They can also be used
for characters specified numerically, for example `[\000-\037]'. If a
range that includes letters is used when caseless matching is set, it
matches the letters in either case. For example, a caseless `[W-c]' is
equivalent to `[][\^_`wxyzabc]', matched caselessly, and if character
tables for the French locale are in use, `[\xc8-\xcb]' matches accented
E characters in both cases.
Unlike in POSIX mode, the character types `\d', `\D', `\s', `\S',
`\w', and `\W' may also appear in a character class, and add the
characters that they match to the class. For example, `[\dABCDEF]'
matches any hexadecimal digit. A circumflex can conveniently be used
with the upper case character types to specify a more restricted set of
characters than the matching lower case type. For example, the class
`[^\W_]' matches any letter or digit, but not underscore.
All non-alphameric characters other than `\', `-', `^' (at the
start) and the terminating `]' are non-special in character classes,
but it does no harm if they are escaped.
Perl 5.6 supports the POSIX notation for character classes, which
uses names enclosed by `[:' and `:]' within the enclosing square
brackets, and `super-sed' supports this notation as well. For example,
[01[:alpha:]%]
matches `0', `1', any alphabetic character, or `%'. The supported
class names are
`alnum'
Matches letters and digits
`alpha'
Matches letters
`ascii'
Matches character codes 0 - 127
`cntrl'
Matches control characters
`digit'
Matches decimal digits (same as \d)
`graph'
Matches printing characters, excluding space
`lower'
Matches lower case letters
`print'
Matches printing characters, including space
`punct'
Matches printing characters, excluding letters and digits
`space'
Matches white space (same as \s)
`upper'
Matches upper case letters
`word'
Matches "word" characters (same as \w)
`xdigit'
Matches hexadecimal digits
The names `ascii' and `word' are extensions valid only in Perl mode.
Another Perl extension is negation, which is indicated by a circumflex
character after the colon. For example,
[12[:^digit:]]
matches `1', `2', or any non-digit.
File: ssed.info, Node: Options setting, Next: Non-capturing subpatterns, Prev: Square brackets, Up: Perl regexps
B.4 Options setting
===================
The settings of the `I', `M', `S', `X' modifiers can be changed from
within the pattern by a sequence of Perl option letters enclosed
between `(?' and `)'. The option letters must be lowercase.
For example, `(?im)' sets caseless, multiline matching. It is also
possible to unset these options by preceding the letter with a hyphen;
you can also have combined settings and unsettings: `(?im-sx)' sets
caseless and multiline matching, while unsets single line matching (for
dots) and extended whitespace interpretation. If a letter appears both
before and after the hyphen, the option is unset.
The scope of these option changes depends on where in the pattern
the setting occurs. For settings that are outside any subpattern
(defined below), the effect is the same as if the options were set or
unset at the start of matching. The following patterns all behave in
exactly the same way:
(?i)abc
a(?i)bc
ab(?i)c
abc(?i)
which in turn is the same as specifying the pattern abc with the `I'
modifier. In other words, "top level" settings apply to the whole
pattern (unless there are other changes inside subpatterns). If there
is more than one setting of the same option at top level, the rightmost
setting is used.
If an option change occurs inside a subpattern, the effect is
different. This is a change of behaviour in Perl 5.005. An option
change inside a subpattern affects only that part of the subpattern
_that follows_ it, so
(a(?i)b)c
matches abc and aBc and no other strings (assuming case-sensitive
matching is used). By this means, options can be made to have
different settings in different parts of the pattern. Any changes made
in one alternative do carry on into subsequent branches within the same
subpattern. For example,
(a(?i)b|c)
matches `ab', `aB', `c', and `C', even though when matching `C' the
first branch is abandoned before the option setting. This is because
the effects of option settings happen at compile time. There would be
some very weird behaviour otherwise.
File: ssed.info, Node: Non-capturing subpatterns, Next: Repetition, Prev: Options setting, Up: Perl regexps
B.5 Non-capturing subpatterns
=============================
Marking part of a pattern as a subpattern does two things. On one
hand, it localizes a set of alternatives; on the other hand, it sets up
the subpattern as a capturing subpattern (as defined above). The
subpattern can be backreferenced and referenced in the right side of
`s' commands.
For example, if the string `the red king' is matched against the
pattern
the ((red|white) (king|queen))
the captured substrings are `red king', `red', and `king', and are
numbered 1, 2, and 3.
The fact that plain parentheses fulfil two functions is not always
helpful. There are often times when a grouping subpattern is required
without a capturing requirement. If an opening parenthesis is followed
by `?:', the subpattern does not do any capturing, and is not counted
when computing the number of any subsequent capturing subpatterns. For
example, if the string `the white queen' is matched against the pattern
the ((?:red|white) (king|queen))
the captured substrings are `white queen' and `queen', and are numbered
1 and 2. The maximum number of captured substrings is 99, while the
maximum number of all subpatterns, both capturing and non-capturing, is
200.
As a convenient shorthand, if any option settings are equired at the
start of a non-capturing subpattern, the option letters may appear
between the `?' and the `:'. Thus the two patterns
(?i:saturday|sunday)
(?:(?i)saturday|sunday)
match exactly the same set of strings. Because alternative branches
are tried from left to right, and options are not reset until the end
of the subpattern is reached, an option setting in one branch does
affect subsequent branches, so the above patterns match `SUNDAY' as
well as `Saturday'.
File: ssed.info, Node: Repetition, Next: Backreferences, Prev: Non-capturing subpatterns, Up: Perl regexps
B.6 Repetition
==============
Repetition is specified by quantifiers, which can follow any of the
following items:
* a single character, possibly escaped
* the `.' special character
* a character class
* a back reference (see next section)
* a parenthesized subpattern (unless it is an assertion; *note
Assertions::)
The general repetition quantifier specifies a minimum and maximum
number of permitted matches, by giving the two numbers in curly
brackets (braces), separated by a comma. The numbers must be less than
65536, and the first must be less than or equal to the second. For
example:
z{2,4}
matches `zz', `zzz', or `zzzz'. A closing brace on its own is not a
special character. If the second number is omitted, but the comma is
present, there is no upper limit; if the second number and the comma
are both omitted, the quantifier specifies an exact number of required
matches. Thus
[aeiou]{3,}
matches at least 3 successive vowels, but may match many more, while
\d{8}
matches exactly 8 digits. An opening curly bracket that appears in a
position where a quantifier is not allowed, or one that does not match
the syntax of a quantifier, is taken as a literal character. For
example, {,6} is not a quantifier, but a literal string of four
characters.(1)
The quantifier `{0}' is permitted, causing the expression to behave
as if the previous item and the quantifier were not present.
For convenience (and historical compatibility) the three most common
quantifiers have single-character abbreviations:
`*'
is equivalent to {0,}
`+'
is equivalent to {1,}
`?'
is equivalent to {0,1}
It is possible to construct infinite loops by following a subpattern
that can match no characters with a quantifier that has no upper limit,
for example:
(a?)*
Earlier versions of Perl used to give an error at compile time for
such patterns. However, because there are cases where this can be
useful, such patterns are now accepted, but if any repetition of the
subpattern does in fact match no characters, the loop is forcibly
broken.
By default, the quantifiers are "greedy" like in POSIX mode, that
is, they match as much as possible (up to the maximum number of
permitted times), without causing the rest of the pattern to fail. The
classic example of where this gives problems is in trying to match
comments in C programs. These appear between the sequences `/*' and
`*/' and within the sequence, individual `*' and `/' characters may
appear. An attempt to match C comments by applying the pattern
/\*.*\*/
to the string
/* first command */ not comment /* second comment */
fails, because it matches the entire string owing to the greediness of
the `.*' item.
However, if a quantifier is followed by a question mark, it ceases
to be greedy, and instead matches the minimum number of times possible,
so the pattern `/\*.*?\*/' does the right thing with the C comments.
The meaning of the various quantifiers is not otherwise changed, just
the preferred number of matches. Do not confuse this use of question
mark with its use as a quantifier in its own right. Because it has two
uses, it can sometimes appear doubled, as in
\d??\d
which matches one digit by preference, but can match two if that is
the only way the rest of the pattern matches.
Note that greediness does not matter when specifying addresses, but
can be nevertheless used to improve performance.
When a parenthesized subpattern is quantified with a minimum repeat
count that is greater than 1 or with a limited maximum, more store is
required for the compiled pattern, in proportion to the size of the
minimum or maximum.
If a pattern starts with `.*' or `.{0,}' and the `S' modifier is
used, the pattern is implicitly anchored, because whatever follows will
be tried against every character position in the subject string, so
there is no point in retrying the overall match at any position after
the first. PCRE treats such a pattern as though it were preceded by \A.
When a capturing subpattern is repeated, the value captured is the
substring that matched the final iteration. For example, after
(tweedle[dume]{3}\s*)+
has matched `tweedledum tweedledee' the value of the captured substring
is `tweedledee'. However, if there are nested capturing subpatterns,
the corresponding captured values may have been set in previous
iterations. For example, after
/(a|(b))+/
matches `aba', the value of the second captured substring is `b'.
---------- Footnotes ----------
(1) It raises an error if `-R' is not used.
File: ssed.info, Node: Backreferences, Next: Assertions, Prev: Repetition, Up: Perl regexps
B.7 Backreferences
==================
Outside a character class, a backslash followed by a digit greater than
0 (and possibly further digits) is a back reference to a capturing
subpattern earlier (i.e. to its left) in the pattern, provided there
have been that many previous capturing left parentheses.
However, if the decimal number following the backslash is less than
10, it is always taken as a back reference, and causes an error only if
there are not that many capturing left parentheses in the entire
pattern. In other words, the parentheses that are referenced need not
be to the left of the reference for numbers less than 10. *Note
Backslash:: for further details of the handling of digits following a
backslash.
A back reference matches whatever actually matched the capturing
subpattern in the current subject string, rather than anything matching
the subpattern itself. So the pattern
(sens|respons)e and \1ibility
matches `sense and sensibility' and `response and responsibility', but
not `sense and responsibility'. If caseful matching is in force at the
time of the back reference, the case of letters is relevant. For
example,
((?i)blah)\s+\1
matches `blah blah' and `Blah Blah', but not `BLAH blah', even though
the original capturing subpattern is matched caselessly.
There may be more than one back reference to the same subpattern.
Also, if a subpattern has not actually been used in a particular match,
any back references to it always fail. For example, the pattern
(a|(bc))\2
always fails if it starts to match `a' rather than `bc'. Because there
may be up to 99 back references, all digits following the backslash are
taken as part of a potential back reference number; this is different
from what happens in POSIX mode. If the pattern continues with a digit
character, some delimiter must be used to terminate the back reference.
If the `X' modifier option is set, this can be whitespace. Otherwise
an empty comment can be used, or the following character can be
expressed in hexadecimal or octal. Note that this applies only to the
LHS pattern; it is not possible yet to specify more than 9
backreferences on the RHS of the `s' command.
A back reference that occurs inside the parentheses to which it
refers fails when the subpattern is first used, so, for example,
`(a\1)' never matches. However, such references can be useful inside
repeated subpatterns. For example, the pattern
(a|b\1)+
matches any number of `a's and also `aba', `ababbaa', etc. At each
iteration of the subpattern, the back reference matches the character
string corresponding to the previous iteration. In order for this to
work, the pattern must be such that the first iteration does not need
to match the back reference. This can be done using alternation, as in
the example above, or by a quantifier with a minimum of zero.
File: ssed.info, Node: Assertions, Next: Non-backtracking subpatterns, Prev: Backreferences, Up: Perl regexps
B.8 Assertions
==============
An assertion is a test on the characters following or preceding the
current matching point that does not actually consume any characters.
The simple assertions coded as `\b', `\B', `\A', `\Z', `\z', `^' and `$'
are described above. More complicated assertions are coded as
subpatterns. There are two kinds: those that look ahead of the current
position in the subject string, and those that look behind it.
An assertion subpattern is matched in the normal way, except that it
does not cause the current matching position to be changed. Lookahead
assertions start with `(?=' for positive assertions and `(?!' for
negative assertions. For example,
\w+(?=;)
matches a word followed by a semicolon, but does not include the
semicolon in the match, and
foo(?!bar)
matches any occurrence of `foo' that is not followed by `bar'.
Note that the apparently similar pattern
(?!foo)bar
finds any occurrence of `bar' even if it is preceded by `foo', because
the assertion `(?!foo)' is always true when the next three characters
are `bar'. A lookbehind assertion is needed to achieve this effect.
Lookbehind assertions start with `(?<=' for positive assertions and
`(?<!' for negative assertions. So,
(?<!foo)bar
achieves the required effect of finding an occurrence of `bar' that
is not preceded by `foo'. The contents of a lookbehind assertion are
restricted such that all the strings it matches must have a fixed
length. However, if there are several alternatives, they do not all
have to have the same fixed length. This is an extension compared with
Perl 5.005, which requires all branches to match the same length of
string. Thus
(?<=dogs|cats|)
is permitted, but the apparently equivalent regular expression
(?<!dogs?|cats?)
causes an error at compile time. Branches that match different length
strings are permitted only at the top level of a lookbehind assertion:
an assertion such as
(?<=ab(c|de))
is not permitted, because its single top-level branch can match two
different lengths, but it is acceptable if rewritten to use two
top-level branches:
(?<=abc|abde)
All this is required because lookbehind assertions simply move the
current position back by the alternative's fixed width and then try to
match. If there are insufficient characters before the current
position, the match is deemed to fail. Lookbehinds, in conjunction with
non-backtracking subpatterns can be particularly useful for matching at
the ends of strings; an example is given at the end of the section on
non-backtracking subpatterns.
Several assertions (of any sort) may occur in succession. For
example,
(?<=\d{3})(?<!999)foo
matches `foo' preceded by three digits that are not `999'. Notice that
each of the assertions is applied independently at the same point in
the subject string. First there is a check that the previous three
characters are all digits, and then there is a check that the same
three characters are not `999'. This pattern does not match `foo'
preceded by six characters, the first of which are digits and the last
three of which are not `999'. For example, it doesn't match
`123abcfoo'. A pattern to do that is
(?<=\d{3}...)(?<!999)foo
This time the first assertion looks at the preceding six characters,
checking that the first three are digits, and then the second assertion
checks that the preceding three characters are not `999'. Actually,
assertions can be nested in any combination, so one can write this as
(?<=\d{3}(?!999)...)foo
or
(?<=\d{3}...(?<!999))foo
both of which might be considered more readable.
Assertion subpatterns are not capturing subpatterns, and may not be
repeated, because it makes no sense to assert the same thing several
times. If any kind of assertion contains capturing subpatterns within
it, these are counted for the purposes of numbering the capturing
subpatterns in the whole pattern. However, substring capturing is
carried out only for positive assertions, because it does not make
sense for negative assertions.
Assertions count towards the maximum of 200 parenthesized
subpatterns.
File: ssed.info, Node: Non-backtracking subpatterns, Next: Conditional subpatterns, Prev: Assertions, Up: Perl regexps
B.9 Non-backtracking subpatterns
================================
With both maximizing and minimizing repetition, failure of what follows
normally causes the repeated item to be evaluated again to see if a
different number of repeats allows the rest of the pattern to match.
Sometimes it is useful to prevent this, either to change the nature of
the match, or to cause it fail earlier than it otherwise might, when the
author of the pattern knows there is no point in carrying on.
Consider, for example, the pattern `\d+foo' when applied to the
subject line
123456bar
After matching all 6 digits and then failing to match `foo', the
normal action of the matcher is to try again with only 5 digits
matching the `\d+' item, and then with 4, and so on, before ultimately
failing. Non-backtracking subpatterns provide the means for specifying
that once a portion of the pattern has matched, it is not to be
re-evaluated in this way, so the matcher would give up immediately on
failing to match `foo' the first time. The notation is another kind of
special parenthesis, starting with `(?>' as in this example:
(?>\d+)bar
This kind of parenthesis "locks up" the part of the pattern it
contains once it has matched, and a failure further into the pattern is
prevented from backtracking into it. Backtracking past it to previous
items, however, works as normal.
Non-backtracking subpatterns are not capturing subpatterns. Simple
cases such as the above example can be thought of as a maximizing
repeat that must swallow everything it can. So, while both `\d+' and
`\d+?' are prepared to adjust the number of digits they match in order
to make the rest of the pattern match, `(?>\d+)' can only match an
entire sequence of digits.
This construction can of course contain arbitrarily complicated
subpatterns, and it can be nested.
Non-backtracking subpatterns can be used in conjunction with
look-behind assertions to specify efficient matching at the end of the
subject string. Consider a simple pattern such as
abcd$
when applied to a long string which does not match. Because matching
proceeds from left to right, `sed' will look for each `a' in the
subject and then see if what follows matches the rest of the pattern.
If the pattern is specified as
^.*abcd$
the initial `.*' matches the entire string at first, but when this
fails (because there is no following `a'), it backtracks to match all
but the last character, then all but the last two characters, and so
on. Once again the search for `a' covers the entire string, from right
to left, so we are no better off. However, if the pattern is written as
^(?>.*)(?<=abcd)
there can be no backtracking for the .* item; it can match only the
entire string. The subsequent lookbehind assertion does a single test
on the last four characters. If it fails, the match fails immediately.
For long strings, this approach makes a significant difference to the
processing time.
When a pattern contains an unlimited repeat inside a subpattern that
can itself be repeated an unlimited number of times, the use of a
once-only subpattern is the only way to avoid some failing matches
taking a very long time indeed.(1)
The pattern
(\D+|<\d+>)*[!?]
([^0-9<]+<(\d+>)?)*[!?]
matches an unlimited number of substrings that either consist of
non-digits, or digits enclosed in angular brackets, followed by an
exclamation or question mark. When it matches, it runs quickly.
However, if it is applied to
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
it takes a long time before reporting failure. This is because the
string can be divided between the two repeats in a large number of
ways, and all have to be tried.(2)
If the pattern is changed to
((?>\D+)|<\d+>)*[!?]
sequences of non-digits cannot be broken, and failure happens
quickly.
---------- Footnotes ----------
(1) Actually, the matcher embedded in `super-sed' tries to do
something for this in the simplest cases, like `([^b]*b)*'. These
cases are actually quite common: they happen for example in a
regular expression like `\/\*([^*]*\*)*\/' which matches C comments.
(2) The example used `[!?]' rather than a single character at the
end, because both `super-sed' and Perl have an optimization that allows
for fast failure when a single character is used. They remember the
last single character that is required for a match, and fail early if
it is not present in the string.
File: ssed.info, Node: Conditional subpatterns, Next: Recursive patterns, Prev: Non-backtracking subpatterns, Up: Perl regexps
B.10 Conditional subpatterns
============================
It is possible to cause the matching process to obey a subpattern
conditionally or to choose between two alternative subpatterns,
depending on the result of an assertion, or whether a previous
capturing subpattern matched or not. The two possible forms of
conditional subpattern are
(?(CONDITION)YES-PATTERN)
(?(CONDITION)YES-PATTERN|NO-PATTERN)
If the condition is satisfied, the yes-pattern is used; otherwise
the no-pattern (if present) is used. If there are more than two
alternatives in the subpattern, a compile-time error occurs.
There are two kinds of condition. If the text between the
parentheses consists of a sequence of digits, the condition is
satisfied if the capturing subpattern of that number has previously
matched. The number must be greater than zero. Consider the following
pattern, which contains non-significant white space to make it more
readable (assume the `X' modifier) and to divide it into three parts
for ease of discussion:
( \( )? [^()]+ (?(1) \) )
The first part matches an optional opening parenthesis, and if that
character is present, sets it as the first captured substring. The
second part matches one or more characters that are not parentheses.
The third part is a conditional subpattern that tests whether the first
set of parentheses matched or not. If they did, that is, if subject
started with an opening parenthesis, the condition is true, and so the
yes-pattern is executed and a closing parenthesis is required.
Otherwise, since no-pattern is not present, the subpattern matches
nothing. In other words, this pattern matches a sequence of
non-parentheses, optionally enclosed in parentheses.
If the condition is not a sequence of digits, it must be an
assertion. This may be a positive or negative lookahead or lookbehind
assertion. Consider this pattern, again containing non-significant
white space, and with the two alternatives on the second line:
(?(?=...[a-z])
\d\d-[a-z]{3}-\d\d |
\d\d-\d\d-\d\d )
The condition is a positive lookahead assertion that matches a
letter that is three characters away from the current point. If a
letter is found, the subject is matched against the first alternative
`DD-AAA-DD' (where AAA are letters and DD are digits); otherwise it is
matched against the second alternative, `DD-DD-DD'.
File: ssed.info, Node: Recursive patterns, Next: Comments, Prev: Conditional subpatterns, Up: Perl regexps
B.11 Recursive patterns
=======================
Consider the problem of matching a string in parentheses, allowing for
unlimited nested parentheses. Without the use of recursion, the best
that can be done is to use a pattern that matches up to some fixed
depth of nesting. It is not possible to handle an arbitrary nesting
depth. Perl 5.6 has provided an experimental facility that allows
regular expressions to recurse (amongst other things). It does this by
interpolating Perl code in the expression at run time, and the code can
refer to the expression itself. A Perl pattern tern to solve the
parentheses problem can be created like this:
$re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
The `(?p{...})' item interpolates Perl code at run time, and in this
case refers recursively to the pattern in which it appears. Obviously,
`sed' cannot support the interpolation of Perl code. Instead, the
special item `(?R)' is provided for the specific case of recursion.
This pattern solves the parentheses problem (assume the `X' modifier
option is used so that white space is ignored):
\( ( (?>[^()]+) | (?R) )* \)
First it matches an opening parenthesis. Then it matches any number
of substrings which can either be a sequence of non-parentheses, or a
recursive match of the pattern itself (i.e. a correctly parenthesized
substring). Finally there is a closing parenthesis.
This particular example pattern contains nested unlimited repeats,
and so the use of a non-backtracking subpattern for matching strings of
non-parentheses is important when applying the pattern to strings that
do not match. For example, when it is applied to
(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
it yields a "no match" response quickly. However, if a standard
backtracking subpattern is not used, the match runs for a very long
time indeed because there are so many different ways the `+' and `*'
repeats can carve up the subject, and all have to be tested before
failure can be reported.
The values set for any capturing subpatterns are those from the
outermost level of the recursion at which the subpattern value is set.
If the pattern above is matched against
(ab(cd)ef)
the value for the capturing parentheses is `ef', which is the last
value taken on at the top level.
File: ssed.info, Node: Comments, Prev: Recursive patterns, Up: Perl regexps
B.12 Comments
=============
The sequence (?# marks the start of a comment which continues ues up to
the next closing parenthesis. Nested parentheses are not permitted. The
characters that make up a comment play no part in the pattern matching
at all.
If the `X' modifier option is used, an unescaped `#' character
outside a character class introduces a comment that continues up to the
next newline character in the pattern.
File: ssed.info, Node: Concept Index, Next: Command and Option Index, Prev: Perl regexps, Up: Top
Concept Index
*************
This is a general index of all issues discussed in this manual, with the
exception of the `sed' commands and command-line options.
[index]
* Menu:
* Additional reading about sed: Other Resources. (line 6)
* ADDR1,+N: Addresses. (line 93)
* ADDR1,~N: Addresses. (line 93)
* Address, as a regular expression: Addresses. (line 27)
* Address, last line: Addresses. (line 22)
* Address, numeric: Addresses. (line 8)
* Addresses, in sed scripts: Addresses. (line 6)
* Append hold space to pattern space: Other Commands. (line 125)
* Append next input line to pattern space: Other Commands. (line 105)
* Append pattern space to hold space: Other Commands. (line 117)
* Appending text after a line: Other Commands. (line 27)
* Backreferences, in regular expressions: The "s" Command. (line 19)
* Branch to a label, if s/// failed: Extended Commands. (line 63)
* Branch to a label, if s/// succeeded: Programming Commands.
(line 22)
* Branch to a label, unconditionally: Programming Commands.
(line 18)
* Buffer spaces, pattern and hold: Execution Cycle. (line 6)
* Bugs, reporting: Reporting Bugs. (line 6)
* Case-insensitive matching: The "s" Command. (line 95)
* Caveat -- #n on first line: Common Commands. (line 20)
* Command groups: Common Commands. (line 50)
* Comments, in scripts: Common Commands. (line 12)
* Conditional branch <1>: Extended Commands. (line 63)
* Conditional branch: Programming Commands.
(line 22)
* Copy hold space into pattern space: Other Commands. (line 121)
* Copy pattern space into hold space: Other Commands. (line 113)
* Delete first line from pattern space: Other Commands. (line 99)
* Disabling autoprint, from command line: Invoking sed. (line 34)
* empty regular expression: Addresses. (line 31)
* Evaluate Bourne-shell commands: Extended Commands. (line 12)
* Evaluate Bourne-shell commands, after substitution: The "s" Command.
(line 86)
* Exchange hold space with pattern space: Other Commands. (line 129)
* Excluding lines: Addresses. (line 116)
* Extended regular expressions, choosing: Invoking sed. (line 83)
* Extended regular expressions, syntax: Extended regexps. (line 6)
* Files to be processed as input: Invoking sed. (line 128)
* Flow of control in scripts: Programming Commands.
(line 11)
* Global substitution: The "s" Command. (line 51)
* GNU extensions, 0 address: Addresses. (line 93)
* GNU extensions, 0,ADDR2 addressing: Addresses. (line 93)
* GNU extensions, ADDR1,+N addressing: Addresses. (line 93)
* GNU extensions, ADDR1,~N addressing: Addresses. (line 93)
* GNU extensions, extended regular expressions: Invoking sed. (line 83)
* GNU extensions, g and NUMBER modifier interaction in s command: The "s" Command.
(line 57)
* GNU extensions, I modifier <1>: The "s" Command. (line 95)
* GNU extensions, I modifier: Addresses. (line 49)
* GNU extensions, N~M addresses: Addresses. (line 13)
* GNU extensions, special escapes <1>: Reporting Bugs. (line 78)
* GNU extensions, special escapes: Escapes. (line 6)
* GNU extensions, special two-address forms: Addresses. (line 93)
* GNU extensions, to basic regular expressions <1>: Reporting Bugs.
(line 51)
* GNU extensions, to basic regular expressions: Regular Expressions.
(line 26)
* GNU extensions, unlimited line length: Limitations. (line 6)
* Goto, in scripts: Programming Commands.
(line 18)
* Greedy regular expression matching <1>: Repetition. (line 73)
* Greedy regular expression matching: Regular Expressions. (line 135)
* Grouping commands: Common Commands. (line 50)
* Hold space, appending from pattern space: Other Commands. (line 117)
* Hold space, appending to pattern space: Other Commands. (line 125)
* Hold space, copy into pattern space: Other Commands. (line 121)
* Hold space, copying pattern space into: Other Commands. (line 113)
* Hold space, definition: Execution Cycle. (line 6)
* Hold space, exchange with pattern space: Other Commands. (line 129)
* In-place editing: Reporting Bugs. (line 85)
* In-place editing, activating: Invoking sed. (line 41)
* In-place editing, Perl-style backup file names: Invoking sed.
(line 52)
* Inserting text before a line: Other Commands. (line 46)
* Labels, in scripts: Programming Commands.
(line 14)
* Last line, selecting: Addresses. (line 22)
* Line length, setting <1>: Other Commands. (line 65)
* Line length, setting: Invoking sed. (line 66)
* Line number, printing: Other Commands. (line 62)
* Line selection: Addresses. (line 6)
* Line, selecting by number: Addresses. (line 8)
* Line, selecting by regular expression match: Addresses. (line 27)
* Line, selecting last: Addresses. (line 22)
* List pattern space: Other Commands. (line 65)
* Mixing g and NUMBER modifiers in the s command: The "s" Command.
(line 57)
* Next input line, append to pattern space: Other Commands. (line 105)
* Next input line, replace pattern space with: Common Commands.
(line 44)
* Non-bugs, in-place editing: Reporting Bugs. (line 85)
* Non-bugs, N command on the last line: Reporting Bugs. (line 31)
* Non-bugs, regex syntax clashes: Reporting Bugs. (line 51)
* Parenthesized substrings: The "s" Command. (line 19)
* Pattern space, definition: Execution Cycle. (line 6)
* Perl-style regular expressions, asserting subpatterns: Assertions.
(line 6)
* Perl-style regular expressions, assertions <1>: Assertions. (line 6)
* Perl-style regular expressions, assertions: Backslash. (line 77)
* Perl-style regular expressions, backreferences <1>: Backreferences.
(line 6)
* Perl-style regular expressions, backreferences: Backslash. (line 18)
* Perl-style regular expressions, case-insensitive <1>: Options setting.
(line 6)
* Perl-style regular expressions, case-insensitive <2>: Square brackets.
(line 27)
* Perl-style regular expressions, case-insensitive <3>: The "s" Command.
(line 95)
* Perl-style regular expressions, case-insensitive: Addresses.
(line 49)
* Perl-style regular expressions, character classes <1>: Square brackets.
(line 6)
* Perl-style regular expressions, character classes: Backslash.
(line 60)
* Perl-style regular expressions, choosing: Invoking sed. (line 91)
* Perl-style regular expressions, comments: Comments. (line 6)
* Perl-style regular expressions, conditional subpatterns: Conditional subpatterns.
(line 6)
* Perl-style regular expressions, escaped sequences: Backslash.
(line 6)
* Perl-style regular expressions, extended <1>: Comments. (line 11)
* Perl-style regular expressions, extended <2>: Options setting.
(line 6)
* Perl-style regular expressions, extended <3>: The "s" Command.
(line 116)
* Perl-style regular expressions, extended: Addresses. (line 70)
* Perl-style regular expressions, lookahead subpatterns <1>: Conditional subpatterns.
(line 40)
* Perl-style regular expressions, lookahead subpatterns: Assertions.
(line 13)
* Perl-style regular expressions, lookbehind subpatterns <1>: Non-backtracking subpatterns.
(line 44)
* Perl-style regular expressions, lookbehind subpatterns: Assertions.
(line 31)
* Perl-style regular expressions, multiline <1>: Options setting.
(line 6)
* Perl-style regular expressions, multiline <2>: Square brackets.
(line 32)
* Perl-style regular expressions, multiline <3>: Circumflex/dollar sign/period.
(line 27)
* Perl-style regular expressions, multiline <4>: The "s" Command.
(line 100)
* Perl-style regular expressions, multiline: Addresses. (line 54)
* Perl-style regular expressions, newlines: Circumflex/dollar sign/period.
(line 6)
* Perl-style regular expressions, non-backtracking subpatterns: Non-backtracking subpatterns.
(line 6)
* Perl-style regular expressions, non-capturing subpatterns: Non-capturing subpatterns.
(line 6)
* Perl-style regular expressions, recursion: Recursive patterns.
(line 6)
* Perl-style regular expressions, recursive patterns: Recursive patterns.
(line 6)
* Perl-style regular expressions, repetitions: Repetition. (line 6)
* Perl-style regular expressions, single line <1>: Repetition.
(line 111)
* Perl-style regular expressions, single line <2>: Options setting.
(line 6)
* Perl-style regular expressions, single line <3>: Square brackets.
(line 32)
* Perl-style regular expressions, single line <4>: Circumflex/dollar sign/period.
(line 41)
* Perl-style regular expressions, single line <5>: The "s" Command.
(line 110)
* Perl-style regular expressions, single line: Addresses. (line 64)
* Perl-style regular expressions, stingy repetitions: Repetition.
(line 73)
* Perl-style regular expressions, syntax: Perl regexps. (line 6)
* Perl-style regular expressions, toggling options: Options setting.
(line 6)
* Portability, comments: Common Commands. (line 15)
* Portability, line length limitations: Limitations. (line 6)
* Portability, N command on the last line: Reporting Bugs. (line 31)
* POSIXLY_CORRECT behavior, bracket expressions: Regular Expressions.
(line 97)
* POSIXLY_CORRECT behavior, enabling: Invoking sed. (line 74)
* POSIXLY_CORRECT behavior, escapes: Escapes. (line 11)
* POSIXLY_CORRECT behavior, N command: Reporting Bugs. (line 46)
* Print first line from pattern space: Other Commands. (line 110)
* Printing line number: Other Commands. (line 62)
* Printing text unambiguously: Other Commands. (line 65)
* Quitting <1>: Extended Commands. (line 36)
* Quitting: Common Commands. (line 30)
* Range of lines: Addresses. (line 80)
* Range with start address of zero: Addresses. (line 93)
* Read next input line: Common Commands. (line 44)
* Read text from a file <1>: Extended Commands. (line 53)
* Read text from a file: Other Commands. (line 78)
* Reformat pattern space: Extended Commands. (line 26)
* Reformatting paragraphs: Extended Commands. (line 26)
* Replace hold space with copy of pattern space: Other Commands.
(line 113)
* Replace pattern space with copy of hold space: Other Commands.
(line 121)
* Replacing all text matching regexp in a line: The "s" Command.
(line 51)
* Replacing only Nth match of regexp in a line: The "s" Command.
(line 55)
* Replacing selected lines with other text: Other Commands. (line 52)
* Requiring super-sed: Extended Commands. (line 69)
* Script structure: sed Programs. (line 6)
* Script, from a file: Invoking sed. (line 120)
* Script, from command line: Invoking sed. (line 115)
* sed program structure: sed Programs. (line 6)
* Selecting lines to process: Addresses. (line 6)
* Selecting non-matching lines: Addresses. (line 116)
* Several lines, selecting: Addresses. (line 80)
* Slash character, in regular expressions: Addresses. (line 41)
* Spaces, pattern and hold: Execution Cycle. (line 6)
* Special addressing forms: Addresses. (line 93)
* ssed extensions, /dev/stderr file <1>: Other Commands. (line 88)
* ssed extensions, /dev/stderr file: The "s" Command. (line 79)
* ssed extensions, /dev/stdin file <1>: Extended Commands. (line 53)
* ssed extensions, /dev/stdin file: Other Commands. (line 78)
* ssed extensions, /dev/stdout file <1>: Other Commands. (line 88)
* ssed extensions, /dev/stdout file <2>: The "s" Command. (line 79)
* ssed extensions, /dev/stdout file: Invoking sed. (line 136)
* ssed extensions, branch if s/// failed: Extended Commands. (line 63)
* ssed extensions, case modifiers in s commands: The "s" Command.
(line 23)
* ssed extensions, checking for their presence: Extended Commands.
(line 69)
* ssed extensions, disabling: Invoking sed. (line 71)
* ssed extensions, evaluating Bourne-shell commands <1>: Extended Commands.
(line 12)
* ssed extensions, evaluating Bourne-shell commands: The "s" Command.
(line 86)
* ssed extensions, in-place editing <1>: Reporting Bugs. (line 85)
* ssed extensions, in-place editing: Invoking sed. (line 41)
* ssed extensions, L command: Extended Commands. (line 26)
* ssed extensions, M modifier <1>: The "s" Command. (line 100)
* ssed extensions, M modifier: Addresses. (line 54)
* ssed extensions, modifiers and the empty regular expression: Addresses.
(line 31)
* ssed extensions, Perl-style regular expressions: Invoking sed.
(line 91)
* ssed extensions, quitting silently: Extended Commands. (line 36)
* ssed extensions, R command: Extended Commands. (line 53)
* ssed extensions, reading a file a line at a time: Extended Commands.
(line 53)
* ssed extensions, reformatting paragraphs: Extended Commands.
(line 26)
* ssed extensions, returning an exit code <1>: Extended Commands.
(line 36)
* ssed extensions, returning an exit code: Common Commands. (line 30)
* ssed extensions, S modifier <1>: The "s" Command. (line 110)
* ssed extensions, S modifier: Addresses. (line 64)
* ssed extensions, setting line length: Other Commands. (line 65)
* ssed extensions, subprocesses <1>: Extended Commands. (line 12)
* ssed extensions, subprocesses: The "s" Command. (line 86)
* ssed extensions, two addresses supported by most commands: Other Commands.
(line 25)
* ssed extensions, writing first line to a file: Extended Commands.
(line 80)
* ssed extensions, X modifier <1>: The "s" Command. (line 116)
* ssed extensions, X modifier: Addresses. (line 70)
* Standard input, processing as input: Invoking sed. (line 130)
* Stream editor: Introduction. (line 6)
* Subprocesses <1>: Extended Commands. (line 12)
* Subprocesses: The "s" Command. (line 86)
* Substitution of text, options: The "s" Command. (line 47)
* Text, appending: Other Commands. (line 27)
* Text, deleting: Common Commands. (line 36)
* Text, insertion: Other Commands. (line 46)
* Text, printing: Common Commands. (line 39)
* Text, printing after substitution: The "s" Command. (line 65)
* Text, writing to a file after substitution: The "s" Command.
(line 79)
* Transliteration: Other Commands. (line 14)
* Unbuffered I/O, choosing: Invoking sed. (line 108)
* Usage summary, printing: Invoking sed. (line 28)
* Version, printing: Invoking sed. (line 24)
* Working on separate files: Invoking sed. (line 98)
* Write first line to a file: Extended Commands. (line 80)
* Write to a file: Other Commands. (line 88)
* Zero, as range start address: Addresses. (line 93)
File: ssed.info, Node: Command and Option Index, Prev: Concept Index, Up: Top
Command and Option Index
************************
This is an alphabetical list of all `sed' commands and command-line
options.
[index]
* Menu:
* # (comments): Common Commands. (line 12)
* --expression: Invoking sed. (line 115)
* --file: Invoking sed. (line 120)
* --help: Invoking sed. (line 28)
* --in-place: Invoking sed. (line 41)
* --line-length: Invoking sed. (line 66)
* --quiet: Invoking sed. (line 34)
* --regexp-extended: Invoking sed. (line 83)
* --regexp-perl: Invoking sed. (line 91)
* --silent: Invoking sed. (line 34)
* --unbuffered: Invoking sed. (line 108)
* --version: Invoking sed. (line 24)
* -e: Invoking sed. (line 115)
* -f: Invoking sed. (line 120)
* -i: Invoking sed. (line 41)
* -l: Invoking sed. (line 66)
* -n: Invoking sed. (line 34)
* -n, forcing from within a script: Common Commands. (line 20)
* -R: Invoking sed. (line 91)
* -r: Invoking sed. (line 83)
* -u: Invoking sed. (line 108)
* : (label) command: Programming Commands.
(line 14)
* = (print line number) command: Other Commands. (line 62)
* a (append text lines) command: Other Commands. (line 27)
* b (branch) command: Programming Commands.
(line 18)
* c (change to text lines) command: Other Commands. (line 52)
* D (delete first line) command: Other Commands. (line 99)
* d (delete) command: Common Commands. (line 36)
* e (evaluate) command: Extended Commands. (line 12)
* G (appending Get) command: Other Commands. (line 125)
* g (get) command: Other Commands. (line 121)
* H (append Hold) command: Other Commands. (line 117)
* h (hold) command: Other Commands. (line 113)
* i (insert text lines) command: Other Commands. (line 46)
* L (fLow paragraphs) command: Extended Commands. (line 26)
* l (list unambiguously) command: Other Commands. (line 65)
* N (append Next line) command: Other Commands. (line 105)
* n (next-line) command: Common Commands. (line 44)
* P (print first line) command: Other Commands. (line 110)
* p (print) command: Common Commands. (line 39)
* q (quit) command: Common Commands. (line 30)
* Q (silent Quit) command: Extended Commands. (line 36)
* r (read file) command: Other Commands. (line 78)
* R (read line) command: Extended Commands. (line 53)
* s command, option flags: The "s" Command. (line 47)
* T (test and branch if failed) command: Extended Commands. (line 63)
* t (test and branch if successful) command: Programming Commands.
(line 22)
* v (version) command: Extended Commands. (line 69)
* w (write file) command: Other Commands. (line 88)
* W (write first line) command: Extended Commands. (line 80)
* x (eXchange) command: Other Commands. (line 129)
* y (transliterate) command: Other Commands. (line 14)
* {} command grouping: Common Commands. (line 50)
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