Your sample would be better written:

#!/usr/bin/perl
use warnings;
use strict;

my $dataStr = <<DATA;
Module: 1

ID:001

Customer : yes

Module: 2

ID:002

Customer : no

Module: 3

ID:003

Customer : yes

Module: 4

ID:004

Customer : no
DATA

my $filename = 'file.txt';
#open my $inFile, '<', $filename or die "Unable to open $filename: $!\
+n";
open my $inFile, '<', \$dataStr;

my $module;
my $id;

while (defined (my $line = <$inFile>)) {
    chomp ($line);
    if ($line =~ /Module:\s*(\S+)/) {
        $module = $1;
        next;
    }

    if ($line =~ /ID:\s*(\S+)/) {
        $line =~ /:\s*/;
        $id = $';
        next;
    }

    if ($line =~ /Customer : (\w+)/i) {
        print "$module and $id\n" if $1 eq 'yes';
        $module = '-- missing module --';
        $id = '-- missing ID --';
    }
}
[download]

which uses three parameter open, lexical file handles, sample data included in the code, checked open result (in the commented "real" open), explicit use of strictures, while loop rather than file slurp and for loop, and improved handling of badly formed data.

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