$ cat sample.txt
a 5
b 6
c 7
d 8

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;
use CGI::FormBuilder;

my @fields = qw(a b c d);
my %values = get_values(shift || '');

my $form = CGI::FormBuilder->new(fields => \@fields, values => \%values);
print "$_ => ", $form->field($_), "\n" for @fields;

sub get_values {
    my $way = shift;
    return (a => 1, b => 2, c => 3, d => 4) unless $way;

    my %fetched;
    if ($way eq 'file') {
        open my $fh, '<', 'sample.txt' or die "open failed: $!\n";
        while (<$fh>) {
            chomp;
            my($key, $value) = split;
            $fetched{$key} = $value;
        }
        close $fh;
    }
    # additional if??

    return %fetched;
}

##</code><code>##

$ perl cfb.pl
a => 1
b => 2
c => 3
d => 4

$ perl cfb.pl file
a => 5
b => 6
c => 7
d => 8