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Shell(3perl)                     Perl Programmers Reference Guide                    Shell(3perl)



NAME
       Shell - run shell commands transparently within perl

SYNOPSIS
          use Shell qw(cat ps cp);
          $passwd = cat('</etc/passwd');
          @pslines = ps('-ww'),
          cp("/etc/passwd", "/tmp/passwd");

          # object oriented
          my $sh = Shell->new;
          print $sh->ls('-l');

DESCRIPTION
   Caveats
       This package is included as a show case, illustrating a few Perl features.  It shouldn't
       be used for production programs. Although it does provide a simple interface for obtaining
       the standard output of arbitrary commands, there may be better ways of achieving what you
       need.

       Running shell commands while obtaining standard output can be done with the "qx/STRING/"
       operator, or by calling "open" with a filename expression that ends with "|", giving you
       the option to process one line at a time.  If you don't need to process standard output at
       all, you might use "system" (in preference of doing a print with the collected standard
       output).

       Since Shell.pm and all of the aforementioned techniques use your system's shell to call
       some local command, none of them is portable across different systems. Note, however, that
       there are several built in functions and library packages providing portable
       implementations of functions operating on files, such as: "glob", "link" and "unlink",
       "mkdir" and "rmdir", "rename", "File::Compare", "File::Copy", "File::Find" etc.

       Using Shell.pm while importing "foo" creates a subroutine "foo" in the namespace of the
       importing package. Calling "foo" with arguments "arg1", "arg2",... results in a shell
       command "foo arg1 arg2...", where the function name and the arguments are joined with a
       blank. (See the subsection on Escaping magic characters.) Since the result is essentially
       a command line to be passed to the shell, your notion of arguments to the Perl function is
       not necessarily identical to what the shell treats as a command line token, to be passed
       as an individual argument to the program.  Furthermore, note that this implies that "foo"
       is callable by file name only, which frequently depends on the setting of the program's
       environment.

       Creating a Shell object gives you the opportunity to call any command in the usual OO
       notation without requiring you to announce it in the "use Shell" statement. Don't assume
       any additional semantics being associated with a Shell object: in no way is it similar to
       a shell process with its environment or current working directory or any other setting.

   Escaping Magic Characters
       It is, in general, impossible to take care of quoting the shell's magic characters. For
       some obscure reason, however, Shell.pm quotes apostrophes ("'") and backslashes ("\") on
       UNIX, and spaces and quotes (""") on Windows.

   Configuration
       If you set $Shell::capture_stderr to 1, the module will attempt to capture the standard
       error output of the process as well. This is done by adding "2>&1" to the command line, so
       don't try this on a system not supporting this redirection.

       Setting $Shell::capture_stderr to -1 will send standard error to the bit bucket (i.e., the
       equivalent of adding "2>/dev/null" to the command line).  The same caveat regarding
       redirection applies.

       If you set $Shell::raw to true no quoting whatsoever is done.

BUGS
       Quoting should be off by default.

       It isn't possible to call shell built in commands, but it can be done by using a
       workaround, e.g. shell( '-c', 'set' ).

       Capturing standard error does not work on some systems (e.g. VMS).

AUTHOR
         Date: Thu, 22 Sep 94 16:18:16 -0700
         Message-Id: <9409222318.AA17072 AT scalpel.com>
         To: perl5-porters AT isu.edu
         From: Larry Wall <lwall AT scalpel.com>
         Subject: a new module I just wrote

       Here's one that'll whack your mind a little out.

           #!/usr/bin/perl

           use Shell;

           $foo = echo("howdy", "<funny>", "world");
           print $foo;

           $passwd = cat("</etc/passwd");
           print $passwd;

           sub ps;
           print ps -ww;

           cp("/etc/passwd", "/etc/passwd.orig");

       That's maybe too gonzo.  It actually exports an AUTOLOAD to the current package (and
       uncovered a bug in Beta 3, by the way).  Maybe the usual usage should be

           use Shell qw(echo cat ps cp);

       Larry Wall

       Changes by Jenda AT Krynicky.cz and Dave Cottle <d.cottle AT csc.nz>.

       Changes for OO syntax and bug fixes by Casey West <casey AT geeknest.com>.

       $Shell::raw and pod rewrite by Wolfgang Laun.

       Rewritten to use closures rather than "eval "string"" by Adriano Ferreira.



perl v5.10.0                                2011-06-30                               Shell(3perl)

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