in reply to
alternation in regexes: to use or to avoid?
Perhaps the following quote from the Camel Book will shed some light on this question:
Short-circuit alternation is often faster than the corresponding regex. So:
print if /one-hump/ || /two/;
is likely to be faster than:
print if /one-hump|two/;
at least for certain values of one-hump and two. This is because the optimizer likes to hoist certain simple matching operations up into higher parts of the syntax tree and do very fast matching with a Boyer-Moore algorithm. A complicated pattern tends to defeat this.
— Tom Christiansen, brian d foy & Larry Wall with Jon Orwant, Programming Perl (4th Edition, 2012), p. 692.
Hope that helps,