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



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@scalpel.netlabs.com>
         To: perl5-porters@isu.edu
         From: Larry Wall <lwall@scalpel.netlabs.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@Krynicky.cz and Dave Cottle <d.cottle@csc.canterbury.ac.nz>.

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

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

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



perl v5.12.5                                     2012-11-03                                       Shell(3pm)