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.
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