use perl's qx{} / `...` operator with a list of arguments

Question

system, exec, open '|-', open2, etc. all allow me to specify the command to run as a list of arguments that will be passed directly to execvp instead of run through a shell.

Even if perl is smart enough to run it directly if it looks like a "simple" command, that saves me the trouble of correctly shell-escaping the arguments with all the nasty pitfalls that it entails.

Example:

open my $out, '|-', $prog, @args;
system $prog, @args;
exec $prog, @args;

instead of

open my $out, "|$prog @args";
system "$prog @args";
exec "$prog @args";

Is there such an equivalent for the qx// operator? Or do you have to always do it by hand eg.

sub slurpcmd {
   open my $h, '-|', @_ or die "open $_[0]|: $!";
   local $/ unless wantarray;
   <$h>
}

Answer 1

A list form of the qx operator is provided by the module IPC::System::Simple as the function capturex (additionally like the other functions in that module, it will throw an exception if there is an execution error or non-zero response code, which you can tweak). Alternatively, you can use Capture::Tiny to wrap a core system call and provide the same behavior, but it also has other functions that can wrap STDERR together or separately from STDOUT.

use strict;
use warnings;
use IPC::System::Simple 'capturex';
my $output = capturex $prog, @args;

use Capture::Tiny 'capture_stdout';
my ($output, $exit) = capture_stdout { system $prog, @args };
# standard system() error checking required here

In core the pipe open is for the most part the only option, aside from IPC::Open3 which is similarly complex but allows directing STDERR as well.

Answer 2

Here are a few simple options.

• String::ShellQuote + qx:

  use String::ShellQuote qw( shell_quote );
  my $cmd = shell_quote(@cmd);
  my $output = `$cmd`;
  

• IPC::System::Simple:

  use IPC::System::Simple qw( capturex );
  my $output = capturex(@cmd)
  

• IPC::Run3:

  use IPC::Run3 qw( run3 );
  run3(\@cmd, \undef, \my $output);
  

• IPC::Run:

  use IPC::Run qw( run );
  run(\@cmd, \undef, \my $output);
  

The first solution involves a shell, but none of the others.

Answer 3

It turns out that (unfortunately) this wasn't an overlook from my part -- the only solution really is to do it with open -| or use one of the external modules listed in the other answers.

The backtick implementation (whether invoked by qx/.../, `...`, or readpipe) is deep down hardwired to accept a single string argument:

PP(pp_backtick)
{
    dSP; dTARGET;
    PerlIO *fp;
    const char * const tmps = POPpconstx;
    const U8 gimme = GIMME_V;
    const char *mode = "r";

    TAINT_PROPER("``");
    if (PL_op->op_private & OPpOPEN_IN_RAW)
        mode = "rb";
    else if (PL_op->op_private & OPpOPEN_IN_CRLF)
        mode = "rt";
    fp = PerlProc_popen(tmps, mode);
    ...

Notice the POPpconstx which pops a single argument from the stack and the use of PerlProc_popen instead of PerlProc_popen_list.