Complete Communications Engineering

In order to parse data to a hash of arrays, first, the data must be in a format that Perl can read.  One format that will work is a text file separated into lines.  If each line has a well-defined format, Perl’s regex engine can be used to parse that format.  The following is an example text file where each line has a well-defined format:


BOOK: Cat In The Hat

COLOR: Green

GAME: Dodgeball


BOOK: If You Give a Mouse a Cookie

GAME: Checkers

COLOR: Orange

GAME: Connect Four

BOOK: Charlie and the Chocolate Factory

GAME: Hide and Seek

In this example, each line contains a category followed by a ‘:’ character, then an item that belongs in that category.  The following Perl code could be used to parse this file:




my %data; # hash of arrays


# Parse the input file line-by-line.  Push each item into the array

# associated with its category.

open my $file, “<data.txt”;

while (my $line = <$file>) {

    if ($line =~ /([A-Z]+):[ \t]*(.*)/) {

        push @{ $data{$1} }, $2;



close $file;


# Print out all items in the GAME category

print “Games:\n”;

foreach my $item (@{ $data{GAME} }) {

    print ”   * $item\n”;


This code first declares an empty hash that will be used to store the data.  Then it parses the input file line-by-line and processes each line that matches a regex pattern.  For each matching line, it finds the corresponding entry in the hash, casts it to an array and pushes on a new item.  After closing the file, the hash of arrays is ready to be used.  The example shows how to print all of the items with a specific key.  The expected output is:

> ./parse.prl


   * Dodgeball

   * Checkers

   * Connect Four

   * Hide and Seek