#!/usr/bin/perl --
use strict;
use warnings;
our %messages = (
    welcome => "
Welcome...
",
    promptfile => "Please enter the name of the file to search:",
    promptword => "Enter a word to search for:",
    byenofile => "No such file exists. Exiting program. Please try again.\n",
    byenoword => "No such word found.\n",
    wordfrequency => "...",
);

## debugging WordFrequency
exit WordFrequency( \"this is in memory test file with test words", "test" );

my $file = Prompt( $messages{welcome}.$messages{promptfile} );
my $word = Prompt( $messages{promptword} );

WordFrequency( $file, $word );
exit;
sub WordFrequency {
    my( $file , $word ) = @_;
    open my($fh), '<', $file or die $messages{byenofile};
    my $freq = 0;
    ...;
    if( $freq ){
        print $messages{wordfrequency}, $freq, "\n";
    } else {
        print $messages{byenoword};
    }
    return $freq;
}
sub Prompt { ... }