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/;

[download]

is likely to be faster than:

print if /one-hump|two/;

[download]

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,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re: alternation in regexes: to use or to avoid? by Athanasius
in thread alternation in regexes: to use or to avoid? by dk

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