How Many Times Did that Word Appear?

Below is simple Perl script for counting how many times a word of interest appears in a text file (Input.txt).  Words of interest are specified in the regular expression stored in the $bucket variable and the number of occurrences of each word is output to a file called WordFreqs.txt.  To illustrate it use, let’s consider the following as the contents of the Input.txt file:

red green yellow blue red

red red yellow

yellow green blue blue green

green red

Now we can run that file through the following Perl script:

#usr/bin/perl

# Copyright 2012- Christopher M. Frenz

# This script is free software - it may be used, copied, redistributed, and/or modified

# under the terms laid forth in the Perl Artistic License

sub by_count {

   $count{$b} <=> $count{$a};

}

open(INPUT, "<Input.txt");

open(OUTPUT, ">WordFreqs.txt");

$bucket='red|blue|green';

while(<INPUT>){

   @words = split(/\s+/);

   foreach $word (@words){

            if($word=~/($bucket)/io){

      $count{$1}++;}

   }

}

foreach $word (sort by_count keys %count) {

   print OUTPUT "$word occurs $count{$word} times\n";

}

close INPUT;

close OUTPUT;

which will yield a WordFreqs.txt file with the following contents:

red occurs 5 times

green occurs 4 times

blue occurs 3 times