MirOS Manual: Shell(3p)


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. Further-
     more, note that this implies that "foo" is callable by file
     name only, which frequently depends on the setting of the
     program's environment.

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

     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 set-
     ting.

     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 true, 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 redirec-
     tion.

     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;

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

         $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.

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