Obligatory... please always put use strict;, use warnings; at the top of your scripts, and here's the idiomatic and recommended three-arg open with lexical file-handles:

# read
open my $fh, '<', 'file.ext' or die $!;

# write
open my $wfh, '>', 'file.ext' or die $!;
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Peppering the code with print statements to try to find out where the code is 'hanging' might help as well.

To get really nitty gritty once the above have been done, throw in a $DB::single = 1; just above where you think the code is hanging, then, on the command line:

# errata removed

$ perl -d script.pl

# 'continue' and stop at your breakpoint with 'c'

main::(script.pl:5):    $DB::single = 1;
  DB<1> c

# step into your variable with 's'

main::(script.pl:6):    my $x = 'y';
  DB<1> s

# display to STDOUT the value of the variable with "x $var"

main::(script.pl:8):    print $x;
  DB<1> x $x
0  'y'
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If it hangs above a print or in debugging your breakpoint, you'll know exactly where to focus your attention.