Shell(3) Perl Programmers Reference Guide Shell(3)
Shell - run shell commands transparently within perl
use Shell qw(cat ps cp);
$passwd = cat('</etc/passwd');
@pslines = ps('-ww'),
# object oriented
my $sh = Shell->new;
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 expres-
sion 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 stan-
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 func-
tions and library packages providing portable implementations of func-
tions 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 essen-
tially a command line to be passed to the shell, your notion of argu-
ments 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 pro-
cess with its environment or current working directory or any other
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 apostro-
phes ("'") and backslashes ("\") on UNIX, and spaces and quotes (""")
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.
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).
Date: Thu, 22 Sep 94 16:18:16 -0700
From: Larry Wall <email@example.com>
Subject: a new module I just wrote
Here's one that'll whack your mind a little out.
$foo = echo("howdy", "<funny>", "world");
$passwd = cat("</etc/passwd");
print ps -ww;
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);
Changes by Jenda@Krynicky.cz and Dave Cottle <firstname.lastname@example.org-
Changes for OO syntax and bug fixes by Casey West <email@example.com>.
$Shell::raw and pod rewrite by Wolfgang Laun.
perl v5.8.6 2001-09-21 Shell(3)