<FUN> To print the identical lines in both files with a one liner from shell, you could use

perl -MDigest::MD5 -ne "print if ($seen{&Digest::MD5::md5_hex($_)}.= @
+ARGV) =~ /10$/" fileA.txt fileB.txt > output.txt
[download]

(see also 36725)

</FUN>

If the files are too big to fit into memory, but you want to deal with the lines as if they were arrays, you could have a look at Tie::File:

use Tie::File;
my @content;
tie (@content, 'Tie::File', $file)
        or die "Error: couldn't tie $file: $!\n";
# .... and treat the filecontent like an array, e.g.
print scalar(@content);
# .....
untie (@content);
[download]

for more details, see perldoc Tie::File, just beware that changes in such a tied array are also done in the tied file.

Best regards,
perl -e "s>>*F>e=>y)\*martinF)stronat)=>print,print v8.8.8.32.11.32"