Is there a way to capture a subroutine's print output to a variable so I can send it to stderr instead?

Question

Suppose we have:

sub test {
        print \"testing\\n\";
}

If there is a case where I want to have it print to stderr instead of stdout, i

Answer 1

Meanwhile, you can also "capture a subroutine's print output to a variable."

Just pass a scalar ref to open:

#! /usr/bin/env perl
use common::sense;
use autodie;

sub tostring (&) {
  my $s;
  open local *STDOUT, '>', \$s;
  shift->();
  $s
}

sub fake {
  say 'lalala';
  say 'more stuff';
  say 1 + 1, ' = 2';
  say for @_;
}

for (tostring { fake(1, 2, 3) }) {
  s/\n/\\n/g;
  say "Captured as string: >>>$_<<<";
}

Output:

Captured as string: >>>lalala\nmore stuff\n2 = 2\n1\n2\n3\n<<<