Something like this should work on most *nix platforms

use List::Util 'first';
use File::Spec::Functions 'catfile';

sub which {
  my $path = first { -x }
               map { catfile $_ => $_[0] } split ':' => $ENV{PATH};
  return $path || "$_ not found in $ENV{PATH}";
}

print "path to $_ is: ", which($_), "\n"
  for qw/ find perl here /;

__output__

path to find is: /usr/bin/find
path to perl is: /usr/bin/perl
path to here is: here not found in /usr/kerberos/bin:/usr/local/bin:/u
+sr/bin:/bin:/usr/X11R6/bin
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