Shell - run shell commands transparently within perl
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.
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.
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.
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
- 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.
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.