IPC::Cmd considered harmful


A rant about IPC::Cmd. Don’t use it.

Recently, I had to do some command-line invocations from Perl. Well, let’s see what we have at our disposal then…

  • system is fine, but too limited. E.g. it does not allow grabbing the output of a command, which I might need;
  • qx is a joke from the past. I mean, not having a list-oriented alternative and forcing the user to do (and possibly forget) quotemeta is something I can’t bear in 2021;
  • IPC::Open2 and IPC::Open3 are in CORE but require some effort to be used, which I’d like to avoid;
  • IPC::Cmd seems interesting, because it’s in CORE and its run_forked seems to hit the sweet spot: it supports providing the command as an array reference, has a bunch of options and provides back everything that’s needed;
  • IPC::Run, IPC::Run3, insert your favourite module here all seem very interesting and flexible, but they are not in CORE and are probably overkill in my case.

Well then, we’re done! IPC::Cmd’s run_forked for the win… right?!?

Well… not so fast.

Interface inconsistency?

One first thing that struck me is the inconsistency in the interface. I mean, function run has the following signature:

run(command => COMMAND, [ optional stuff... ])

i.e. the COMMAND MUST be preceded by the command keyword, whereas run_forked has this:

run_forked(COMMAND, \%options)

Anyway, my intention is to use one of the two only, so let’s move on…

What’s with that newline

Another weird thing I noticed is that providing some text using the child_stdin option adds a newline at the end.

Well, in my specific case I’m not terribly annoyed, except that I am because I can’t anticipate everything and that stray newline might break something in the future.

Cram the command in a string? REALLY?!?

The thing I could not believe was the following in the code though:

    if (ref($cmd) eq 'ARRAY') {
        $cmd = join(" ", @{$cmd});

What. The. Fraking. Frak.

After having learned about how I should always force the use of the system/exec that avoids invoking the shell… I consider this a stab on the back.

I don’t know the reasons - maybe backwards compability? - but this is so unexpected in a CORE module with 16+ signs of appreciation in metacpan that’s almost unbelievable.


Don’t use IPC::Cmd.

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