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Your issue appears to be that "'121'\n" and "'121'" are different strings. If you'd like to be newline insensitive (which would also address the extra newlines in your output), use chomp:
use strict; use warnings; my $f2 = 'cat_mapping_in_A.txt'; my $f1 = 'cat_mapping_in_B.txt'; my $outfile = '1.txt'; my %results = (); open FILE1, "$f1" or die "Could not open file: $! \n"; while(my $line = <FILE1>){ chomp $line; $results{$line}=1; } close(FILE1); open FILE2, "$f2" or die "Could not open file: $! \n"; while(my $line =<FILE2>) { chomp $line; $results{$line}++; } close(FILE2); open (OUTFILE, ">$outfile") or die "Cannot open $outfile for writing \ +n"; foreach my $line (keys %results) { print OUTFILE "$line\n" if $results{$line} == 1; } close OUTFILE;

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Re: ignore duplicates and show unique values between 2 text files by kennethk
in thread ignore duplicates and show unique values between 2 text files by perlnoobster

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