I'd suggest using open. Breifly, it would work something like this:

#!/usr/bin/perl -w
use strict;

my($program) = 'cat';
my(@ary);

open(CAT,"$program ~/foo.txt |") || die "Unable to run $program: $!\n"
+;
foreach (<CAT>) {
  push @ary, $_;
  print "$_";
}

close(CAT);
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Of course, TIMTOWTDI, with backticks, for example. However, this method has worked well for me in the past.

Note: Taint checking is left as an exercise for the reader.

Hope that helps,
Shendal