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=head1 TITLE

Request For New Pragma: Shell

=head1 VERSION

Maintainer: Bryan C. Warnock <bwarnock@gtemail.net>
Date: 5 Aug 2000
Last Modified: 18 Sep 2000
Mailing List: perl6-language@perl.org
Number: 42
Version: 3
Status: Frozen

=head1 CHANGES

Added the heavy footnoting about name-clobbering with C<Shell.pm>.

=head1 ABSTRACT

Perl 6 should add a new pragma, previously thought to be called C<shell>, but
now called something else, although I don't know what. So I'll stick with
C<shell>. Although quite frankly C<Bob> would be just fine with me.

=head1 DESCRIPTION

The shell that Perl uses for shell interpretation is defined at compile
time. Furthermore, it is optimized away when no metacharacters are found
within the command string.

There are times when one may need (or desire) to change the shell used for
interpretation, as well as force shell interpretation, regardless of
optimization, for consistency's sake.

Perl runs on many platforms. Many of these platforms, either by default,
desire, or need, may have multiple command interpreters that Perl may want to
interface with by default. (ie, through the use of backticks or system().)

Perl is not just a glue language, but a SuperGlue language. I ab^H^Huse
Perl to interact with a lot of home-grown command interpreters as either a
driver, a hardware controller, or Expect-type engine. It's a lot more
DWIMmer when I can operate in that environment, vice the standard OS one.

Furthermore, there are times when speed be damned! I need every `` to go
through the command interpreter in order to get back consistent results, and
I don't want to have to mangle the output string in order to force a
metacharacter.

It is important, however, that this be lexically scoped. One can't really
afford to have some unknown module expect /bin/sh and accidentally send the
command to turn on a robot's "Kill Human" mode, for instance.

=head1 MOTIVATORS

Laziness, and perhaps a bit of Hubris.

=head1 IMPLEMENTATION

This was an easy hack in Perl 5, except for the scoping issue. Ideally,
there'd be a -force flag to check, and a method to change the location of the
shell, the shell arguments, and perhaps what is defined as a shell
metacharacter.

=head2 SUMMARY OF IMPLEMENTATION

See above. I hacked this for Perl 5 in about two minutes, minus the scoping,
which I never could figure out. :-( The scoping lament is continued in RFC
40.

=head2 IMPACT

=over 4

=item *

Impact on Perl 5. Mutual compatibility between Perl 5 and Perl 6, with the
exception of C<use shell> and the semantics it would add. (Obviously, other
changes to the language notwithstanding.)

=back

=head2 UNKNOWNS

=over 4

=item *

What if the interfaced modules return things that `` and system() don't
expect?

=back

=head1 STATUS

Frozen. There has been little discussion, other than pointing out that Shell
is already a module, and on platforms that are case insensitive, the
two would clobber. Furthermore, it was agreed that this C<shell>
doesn't fit well into that C<Shell>. Hence, this pragma is more or
less the ubiquitous "player to be named later."

=head1 REFERENCES

RFC 40: Module Scope Control.

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