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Which shows that sub athanasius is up to 5 times faster than sub karlgoethebier. Even easier to see when supplying a positive COUNT value to timethese:

#! perl use strict; use warnings; use Benchmark qw( :hireswallclock cmpthese timethese ); my $string = ".co.uk/Jobs/Company-Sector/C8A6446X4PND86M9WYJ/Tradewind +/?APath=2.21.0.0.0"; cmpthese( timethese ( 1_000_000, { 'karlgoethebier' => sub { $string =~ m/.+\/.+\/.+\/.+\/(.+)\/.+/; retu +rn $1; }, 'athanasius' => sub { return (split '/', $string)[4] }, } ) );

Output:

13:09 >perl 390_SoPW.pl Benchmark: timing 1000000 iterations of athanasius, karlgoethebier... athanasius: 5.19894 wallclock secs ( 5.15 usr + 0.00 sys = 5.15 CPU) + @ 194250.19/s (n=1000000) karlgoethebier: 20.2485 wallclock secs (20.08 usr + 0.00 sys = 20.08 +CPU) @ 49808.24/s (n=1000000) Rate karlgoethebier athanasius karlgoethebier 49808/s -- -74% athanasius 194250/s 290% -- 13:16 >

Not really surprising, since regexen with quantifiers can be expensive:

Avoid regular expressions with many quantifiers.... Such patterns can result in exponentially slow backtracking behavior unless the quantified subpatterns match on their first “pass”.
The Camel Book, 4th Edition, p. 693.

So, what happens if we limit the backtracking?

#! perl use strict; use warnings; use Benchmark qw( :hireswallclock cmpthese timethese ); my $string = ".co.uk/Jobs/Company-Sector/C8A6446X4PND86M9WYJ/Tradewind +/?APath=2.21.0.0.0"; cmpthese( timethese ( 1_000_000, { 'karlgoethebier' => sub { $string =~ m/.+\/.+\/.+\/.+\/(.+)\/.+/; retu +rn $1; }, 'karlgoethebier2' => sub { $string =~ m/.+?\/.+?\/.+?\/.+?\/(.+?)\/.+/; + return $1; }, 'athanasius' => sub { return (split '/', $string)[4] }, } ) );

Result:

13:28 >perl 390_SoPW.pl Benchmark: timing 1000000 iterations of athanasius, karlgoethebier, ka +rlgoethebier2... athanasius: 4.91799 wallclock secs ( 4.88 usr + 0.00 sys = 4.88 CPU) + @ 204792.14/s (n=1000000) karlgoethebier: 20.1721 wallclock secs (20.05 usr + 0.00 sys = 20.05 +CPU) @ 49885.26/s (n=1000000) karlgoethebier2: 2.55908 wallclock secs ( 2.53 usr + 0.00 sys = 2.53 + CPU) @ 395569.62/s (n=1000000) Rate karlgoethebier athanasius karlgoethebie +r2 karlgoethebier 49885/s -- -76% -8 +7% athanasius 204792/s 311% -- -4 +8% karlgoethebier2 395570/s 693% 93% +-- 13:29 >perl 390_SoPW.pl

The regex is now significantly faster than split-with-subscript. Interesting!

Athanasius <°(((><contra mundum


In reply to Re^4: Question on Regex by Athanasius
in thread Question on Regex by Anonymous Monk

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