Tom Allison wrote:
>
> Also, is there any reason NOT to end the regex with /o to improve
> performance?
perldoc -q '/o'
Found in /usr/lib/perl5/5.8.6/pod/perlfaq6.pod
What is "/o" really for?
Using a variable in a regular expression match forces a
re‐evaluation (and perhaps recompilation) each time the regular
expression is encountered. The "/o" modifier locks in the regex
the first time it’s used. This always happens in a constant
regular expression, and in fact, the pattern was compiled into
the internal format at the same time your entire program was.
Use of "/o" is irrelevant unless variable interpolation is used
in the pattern, and if so, the regex engine will neither know nor
care whether the variables change after the pattern is evaluated
the very first time.
"/o" is often used to gain an extra measure of efficiency by not
performing subsequent evaluations when you know it won’t matter
(because you know the variables won’t change), or more rarely,
when you don’t want the regex to notice if they do.
For example, here’s a "paragrep" program:
$/ = ’’; # paragraph mode
$pat = shift;
while (<>) {
print if /$pat/o;
}
John
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