


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


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



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


       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");



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


           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.
































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