Shell

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



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 fea-
       tures.  It shouldn’t be used for production programs. Although it does
       provide a simple interface for obtaining the standard output of arbi-
       trary 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 col-
       lected standard output).

       Since Shell.pm and all of the aforementioned techniques use your sys-
       tem’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 individ-
       ual 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 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 redirection.

       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 cur-
       rent 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.canter-
       bury.ac.nz>.

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

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



perl v5.8.8			  2001-09-21			     Shell(3)