# Verify that there are no duplicates.
perl -nE 'say $_ if $seen{$_}++;' testfile.txt
# We want no output.


# Verify that there are 6000000 lines.
perl -nE '$count++; END{ say $count; }' testfile.txt
# We want 6000000 as the output.


# Verify that we only have digits between a..z and 3, 4, 6, 7, 9.
perl -nE 'say "$. : $_" if m/[^a-z34679\n]/' testfile.txt
# We want no output.