#!/usr/bin/perl

sub with_stdin
{
  my $surrogate_input = shift;
  my $test_sub = shift;

  local *STDIN;
  open STDIN, '<', \$surrogate_input;

  &{$test_sub};
}

sub test_sub {
  print "Arguments: @_\n";
  while(<STDIN>) {
    print "** $_";
  }
}

with_stdin <<'EOS'
Once
Upon
A Time
EOS
, \&test_sub, qw(arg1 arg2 arg3);
[download]

Just put the input in a file and reopen STDIN to read from that file before you call your sub.

-sauoq
"My two cents aren't worth a dime.";

2005-10-28 Retitled by planetscape, as per Monastery guidelines
Original title: 'Re: Testing a subrutine with STDIN'

Similar to the external file approach, for simple tests, I've gotten some mileage out of just pointing STDIN to DATA.

use warnings;

*STDIN = *DATA;

print while <STDIN>;

__DATA__
Hello world
Once upon a time...
How now brown cow
[download]

Another approach that doesn't need an external file is to use IO::String to create an in-memory file and alias STDIN to that. By directly changing the contents of the underlying scalar, you can control what will next be read from the in-memory file.