The idea of IPC::System::Simple is that you can replace this (from perldoc -f system):

system("some_command");

if ($? == -1) {
    die "failed to execute: $!\n";
}
elsif ($? & 127) {
    die "child died with signal %d, %s coredump\n",
   ($? & 127),  ($? & 128) ? 'with' : 'without';
}
else {
   die "child exited with value %d\n", $? >> 8;
}
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with this:

use IPC::System::Simple qw(run);

run("some_command");
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Currently this works very well, but it's currently got a small problem detecting errors on Win32 systems.

Interestingly enough, the exact same problem occurs under Unix, but Perl only uses the shell under Unix when it's called with a single argument, and then only when it contains metacharacters. When the Unix shell is used, we can't tell the difference between a command failing to start, and one that runs to completion and merely returns an exit value of 127.

I'm intending for IPC::System::Simple to always mimic the Unix behaviour of system, regardless of the platform used. In other words:

use IPC::System::Simple qw(run);

run("foo");               # No meta-chars, shell never used
run("bar | bar");         # Meta-chars, shell always used.
run("foo", "bar", "<baz") # Multi-arg, shell never used.
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In the above examples, the first and third examples would be passed to the shell under Win32 if foo was not in the current working directory and we used system() instead. Neither would use the shell under Unix and modern releases of Perl.

One advantage of bypassing the shell is that we can also return the full 16-bit exit code returned by Windows processes. When using system() this is truncated to 8 bits.

This RFC is intended primarily as a sanity check. I feel I have a compelling reason to deviate from Perl's behaviour of system() under Windows; the current implementation is inconsistent compared to its Unix counterpart, it fails in an ambiguous way, and loses bits of the return value. Can anyone find me a compelling argument not to do this?

Further references:

• Perlmonks: $? set to strange values on failure under Win32
• Perlbug: #43631: Multi-argument system() invokes the shell under Win32
• Perlmonks: Modules which improve system() ?
• CPAN: IPC::System::Simple