As long as all the alternates are fixed strings, perl 5.10.0 onwards will compile all alternates into a single data structure called a trie, which is a kind of tree that allows for all alternatives to be scanned for in a single pass. So it's very efficient. The trick is to keep any meta-stuff outside, e.g. 
/\s+(abc|def|ghij|....)/       # good, will be optimised
/(\s+abc|\s+def|\s+ghij|....)/ # bad

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Dave.

In reply to Re: Warning about playing with matches by dave_the_m
in thread Warning about playing with matches by ExReg

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