# AliceUtils.pm

package AliceUtils;

sub safe_filename {
  my $string = shift;
  $string =~ s{\W}{}g;
  $string = "untitled" if !$string;
  return $string;
}

1;

# BobUtils.pm

package BobUtils;

use AliceUtils;  # Make sure it's loaded!

sub save_data {
  my ( $filename, $data ) = @_;
  my $safe_filename = AliceUtils::safe_filename( $filename ) . ".txt";
  open my $fh, '>', $safe_filename or die;
  print $fh $data or die;
  close $fh or die;
  return $safe_filename;
}

1;

# example.pl

use AliceUtils;
use BobUtils;

BobUtils::save_data( "my file", "Hello world!\n" );