It looks like you have plenty to work with, but here's my solution:

open my $file, 'in.txt' || die "Couldn't open file: $!\n";    #better 
+way to make file handles
foreach (<$file>){    #for each line
    push @matches, $_ if (/abc/);    #keep them in an array if they ma
+tch
}
print @matches;    #print the matches
print "Total matches: ",scalar(@matches),"\n";    #print the number of
+ matches
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