Updated: use values of 6, 7 as below to account for \n in length().

#!/usr/bin/perl -w
use strict;

#This script selects only the five-letter and six-letter words from a 
+list of words

open FH1, "all_words.txt" or die $!;
open (FH2, '>>trimmed_words.txt') or die $!;

while (<FH1>)
{
     if (length ==5 or length==6)
       {print FH2 };
}
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Ooops the deadly "off by one problem!". I guess length counts the "\n" at the end of line!

while (<DATA>)
{
   if (length ==6 or length==7) {print;}
}
__DATA__
123
1234
12345
123456
1234567
12345678
==============
prints:
12345
123456
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