Comments for Laufeyjarson writes...

Comment on Stripping whitespace from both ends of a string… by John Wiersba

John Wiersba — Fri, 05 Mar 2010 20:49:33 +0000

I think the hands down winner is $str =~ s/^\s+//; $str =~ s/\s+\z//;

It says exactly what you want and it’s the fastest. No need to “optimize” with a single regex. Although dami’s postfix-for form is 7 characters shorter, the need for a comma instead of semicolon is a blemish, plus it’s about 25% slower.

#!/usr/bin/perl -w
use strict;
use Benchmark;
use vars qw($str1);
$str1 = ” asf asd fasd fasd f asdf asd asdf as fsda fasdf “;
timethese( -5, {
test1_0 => ‘ $str = $str1; $str =~ s/^\s+|\s+\z//g ‘,
test1_1 => ‘ $str = $str1; $str =~ s/^\s*|\s*\z//g ‘,
test1_2 => ‘ $str = $str1; $str =~ s/^\s+|\s+$//g ‘,
test1_3 => ‘ $str = $str1; $str =~ s/^\s*|\s*$//g ‘,
test2_0 => ‘ $str = $str1; $str =~ s/^\s+//; $str =~ s/\s+\z// ‘,
test2_1 => ‘ $str = $str1; $str =~ s/^\s+//; $str =~ s/\s+$// ‘,
test2_2 => ‘ $str = $str1; $str =~ s/^\s*//; $str =~ s/\s*\z// ‘,
test2_3 => ‘ $str = $str1; $str =~ s/^\s*//; $str =~ s/\s*$// ‘,
test3 => ‘ $str = $str1; s/^\s+//, s/\s+\z// for $str ‘,
});

Benchmark: running test1_0, test1_1, test1_2, test1_3, test2_0, test2_1, test2_2, test2_3, test3 for at least 5 CPU seconds…
test1_0: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 185981.10/s (n=983840)
test1_1: 5 wallclock secs ( 5.22 usr + 0.00 sys = 5.22 CPU) @ 154480.84/s (n=806390)
test1_2: 6 wallclock secs ( 5.22 usr + 0.00 sys = 5.22 CPU) @ 188475.10/s (n=983840)
test1_3: 5 wallclock secs ( 5.25 usr + 0.00 sys = 5.25 CPU) @ 154564.00/s (n=811461)
test2_0: 5 wallclock secs ( 5.26 usr + 0.01 sys = 5.27 CPU) @ 672072.87/s (n=3541824)
test2_1: 6 wallclock secs ( 5.44 usr + 0.00 sys = 5.44 CPU) @ 651070.77/s (n=3541825)
test2_2: 5 wallclock secs ( 5.17 usr + 0.00 sys = 5.17 CPU) @ 248851.26/s (n=1286561)
test2_3: 5 wallclock secs ( 5.23 usr + 0.00 sys = 5.23 CPU) @ 241523.71/s (n=1263169)
test3: 4 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 526948.02/s (n=2787555)

Comment on Stripping whitespace from both ends of a string… by dami

dami — Tue, 02 Mar 2010 19:58:55 +0000

Jeffrey Friedl recommends using 2 regexes. But you can do it in one line :

s/^\s+//, s/\s+$// for $str;

Comment on Stripping whitespace from both ends of a string… by mattp

mattp — Tue, 02 Mar 2010 14:40:21 +0000

its slower due to the backtracking required from the combination of two greedy quantifiers with the one non greedy.
to quote knuth .. premature optimization is the root of all evil

Comment on Stripping whitespace from both ends of a string… by Hercynium

Hercynium — Tue, 02 Mar 2010 05:34:55 +0000

What about:

$str =~ s/^\s*|\s*$//g

Seems clearer and will probably be faster.

Comment on Stripping whitespace from both ends of a string… by Dave Rolsky

Dave Rolsky — Tue, 02 Mar 2010 04:05:34 +0000

Yes, it’s slower, but look at the absolute speed. The “slow” version can still execute 440,000 or so per minute!

Write code as clearly as possible, _then_ optimize the slow parts. This is what profilers are for.

This sort of premature micro-optimization makes for messy code that may actually be no faster than clean code.

Also, I think the simplest way to write it is …

$str =~ s/^\s+|\s+$//g;

Comment on Stripping whitespace from both ends of a string… by Yanick

Yanick — Tue, 02 Mar 2010 03:50:28 +0000

What about

$str =~ s/^\s+|\s+$//g

It’s faster, and not too obtuse.

Comment on Stripping whitespace from both ends of a string… by Yanick

Yanick — Tue, 02 Mar 2010 03:49:13 +0000

What about

$str =~ s/^\s+|\s+$//g

Comment on Stripping whitespace from both ends of a string… by Mark Grimes

Mark Grimes — Tue, 02 Mar 2010 03:32:52 +0000

What about:

$str =~ s/^\s*|\s*$//g;

I can’t test or benchmark it right now, but I know I’ve used something along these lines before.

Comment on Stripping whitespace from both ends of a string… by zloyrusskiy

zloyrusskiy — Tue, 02 Mar 2010 03:31:09 +0000

I’m using:

s/(?:^\s+|\s+$)//g

it’s one regular expression + has good speed

Comment on Stripping whitespace from both ends of a string… by Adam Kennedy

Adam Kennedy — Tue, 02 Mar 2010 03:19:19 +0000

$str =~ s/(?:^\s+|\s+$)//g;