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.