Re^3: Problem with pre-compiled regex

Compiling a short and simple regex that consists of only one string literal is so fast that you'll probably have trouble to come up with a benchmark to measure it. So if there is a difference, it'll be too small to be easily observable.

I also think that Perl has an internal cache that avoids recompiling the same regex all over again.

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Comment on Re^3: Problem with pre-compiled regex

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Re^4: Problem with pre-compiled regex by ikegami (Patriarch) on Jan 18, 2012 at 07:03 UTC
I also think that Perl has an internal cache that avoids recompiling the same regex all over again. The ops that compile regex patterns (qr//, m// and s///) remember the last pattern they compiled. `_ _ _ \| \| \| \| \| >perl -Mre=debug -e"for (qw( a a a a b b b a )) { qr/$_/ }" 2>&1 \| fin +d "Compiling" Compiling REx "a" Compiling REx "b" Compiling REx "a"` [download] So if you compile the same pattern many times in a row, you'll get savings. It's useful for code that looks like `for my $pat (...) { for my $string (...) { ... $string =~ /$pat/ ... } }` [download] But not for code that looks like `for my $string (...) { for my $pat (...) { ... $string =~ /$pat/ ... } }` [download]	[reply] [d/l] [select]

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Re^4: Problem with pre-compiled regex
by ikegami (Patriarch) on Jan 18, 2012 at 07:03 UTC

I also think that Perl has an internal cache that avoids recompiling the same regex all over again.

The ops that compile regex patterns (qr//, m// and s///) remember the last pattern they compiled.

                            _       _     _
                             |     | |   | |
>perl -Mre=debug -e"for (qw( a a a a b b b a )) { qr/$_/ }" 2>&1 | fin
+d "Compiling"
Compiling REx "a"
Compiling REx "b"
Compiling REx "a"
[download]

So if you compile the same pattern many times in a row, you'll get savings.

It's useful for code that looks like

for my $pat (...) {
   for my $string (...) {
      ... $string =~ /$pat/ ...
   }
}
[download]

But not for code that looks like

for my $string (...) {
   for my $pat (...) {
      ... $string =~ /$pat/ ...
   }
}
[download]

[reply]
[d/l]
[select]