Question

The code below works exactly as I want it to in my perl script. However, it takes forever to run through very large files. Would someone know a perl alternative to my grep command?

my $print = `grep --after-context=3 $line $inputfile`;
print OUTFILE $print

To explain the code above: it simply finds a line (called $line) in the input file (called $inputfile) and prints the match it found and the three lines following the match (from the $inputfile) to my outfile (called OUTFILE).

Cheers!

Answer 1

While there’s some overhead in launching a grep subprocess, it’s a fixed amount, unrelated to the size of the file. Unless you’ve got a very bad implementation of grep, you’re not going to be able to improve the search time in pure Perl. In fact, searching a large file using Perl is likely to be slower than grep, which is optimized solely for searching files.

If you’re only looking for the first match, you might want to add --max-count=1 to your grep command. This will cause grep to quit immediately, instead of reading the rest of the file to find additional matches.