Hello rahulme81,

Your while loop contains this line:

my ($pattern,$id) = (split /\s+/, $_)[0,4];
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which sets $pattern and $id to the first and fifth fields, respectively, in the current line. But the data you show contains only three fields per line, so you should have:

my ($pattern, $id) = (split /\s+/)[0, 2];
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(Note that the $_ is unnecessary here.) Also, this line:

if ( $_ =~ m/^$pattern/ ) {
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tests whether the current line begins with $pattern. But you just initialized $pattern as the first field in the line, so how could this fail? (Well, it will fail if the line begins with whitespace, but I don’t think that’s what you had in mind.) You need to test $pattern against a pre-determined pattern, for example:

...
my $pattern_to_find = '4567';
...
while (<MAST>) {
    my ($pattern, $id) = (split /\s+/)[0, 2];
    ...
    if ($pattern eq $pattern_to_find) {
        ...
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Hope that helps,