I have to disagree. Depending on how complex your regex is and what you want to do once you find the string in the file, grep is usually NOT more efficient than Perl. One major reason is that grep uses a text-directed regex engine. It searches for the "best match" in a string so it has to search through the whole string even if it finds a match before it reaches the end. Perl uses a regex-directed engine and it returns the "left-most match". So the instant it finds a match, the Perl regex engine returns that match and moves on.

I've seen this demonstrated when dealing with very large log files(>2G). Perl was able to do in a few minutes what it was taking grep 10+ minutes to accomplish.

Check out Jeffrey Friedl's book Mastering Regular Expressions. It's an absolutely fascinating read on regexes and regex engines.

Later

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