in reply to matching the contents of two (2) files

First, what does doing this buy you that using diff doesn't? Use the right tool for the right job.

Second, You will want to use a hash, not an array. (I'm abbreviating here. Add the excellent fileopen stuff you're doing.) 

chomp( my @first = <FIRST> );
chomp( my @last = <LAST> );

my %last_names;
undef @last_names{ @last };

foreach my $name (@first ) {
    next if exists $last_names{ $name };
    print "$name\n";
}

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Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

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Re^2: matching the contents of two (2) files
by Roy Johnson (Monsignor) on Mar 10, 2005 at 21:07 UTC
    If you're going to abbreviate, abbreviate :-) 
    my %hash;
@hash{<LAST>} = (); # Death to the undef trick!

exists $hash{$_} or print while <FIRST>;

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    Caution: Contents may have been coded under pressure.
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[d/l]
      Let's see ... that's about 70 characters. 
      #234567890#234567890#234567890#234567890
-p BEGIN{@x{+pop}=()}exists$x{$_}||next

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      That's 39 characters. You have to run it as so from the command line. 
      perl -p -e 'BEGIN{@x{+pop}=()}exists$x{$_}||next' FIRST.txt LAST.txt >
+ MISSING.txt

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      This is really untested code, but it _should_ work. :-)

      Being right, does not endow the right to be rude; politeness costs nothing.
      Being unknowing, is not the same as being stupid.
      Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
      Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

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