Re: what is the function should I need to use for trim white spaces ?

I tend to do it:

use strict;
use warnings;

my $before = "   some text   ";
($_ = $before) =~ s/^\s+|\s+$//g;
print ">$before<\n";
print "|$_|\n";
[download]

Prints:

>   some text   <
|some text|
[download]

I guess this is sufficiently light weight that it is thought a function is not required. Does seem a slight omission though.

DWIM is Perl's answer to Gödel

Comment on Re: what is the function should I need to use for trim white spaces ? Select or Download Code

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Re^2: what is the function should I need to use for trim white spaces ? by ikegami (Patriarch) on Jan 11, 2006 at 19:32 UTC
Assinging to $_ without localizing it is dangerous. `(local $_ = $before) =~ s/^\s+\|\s+$//g;` or `(my $after = $before) =~ s/^\s+\|\s+$//g;` should be used in just almost all cicumstances.	[reply] [d/l] [select]
Re^2: what is the function should I need to use for trim white spaces ? by rational_icthus (Sexton) on Jan 11, 2006 at 19:52 UTC
I think the alternation in the s/^\s+\|\s+$// version causes significant time costs in large applications. I often work with tab-delimited files containing hundreds of thousands of lines. If I'm tab-splitting these lines and then trimming each one, I'm going to pick the double-regex approach each time. I wrote some quick code that benchmarked the double-regex vs single-regex approach against three strings. `use Benchmark; my @words = ('trim_unneeded',' front trim only','rear trim only ',' + both side trim '); for my $word (@words){ print "Benchmarking $word...\n\n"; timethese(1_000_000, {double => sub{ $word =~ s/^\s+//; $word =~ s +/\s+$//; }, single => sub{ $word =~ s/^\s+\|\s+$//; }}) }` [download] The code was run on a Celeron D 2.8 GHz machine running XP with the following results: 'trim_unneeded' Single Regex: 0.45 seconds Double Regex: 2.27 seconds ' front trim only' Single Regex: 0.67 seconds Double Regex: 2.66 seconds 'rear trim only ' Single Regex: 0.67 seconds Double Regex: 2.45 seconds ' both side trim ' Single Regex: 0.66 seconds Double Regex: 2.44 seconds That's after only 1,000,000 trims. In a 800,000 line file with 50 columns per line, we're talking about 40,000,000 trims. Assuming a linear scale, that means I give up about a minute of processing time per file per run. That's far less than the time it would have taken me to type two regexes. Admittedly, it's a small optimization, and only valid for those who are processing files on the scale that I do, but for most people who end up typing the 'trim regex' often enough to complain about it on perlmonks, it probably applies.	[reply] [d/l]
Re^3: what is the function should I need to use for trim white spaces ? by phaylon (Curate) on Jan 14, 2006 at 23:14 UTC
"I think the alternation in the s/^\s+\|\s+$// version causes significant time costs in large applications." Wait, isn't the single regex faster in your benchmark? "Single Regex: 0.45 seconds Double Regex: 2.27 seconds" Ordinary morality is for ordinary people. -- Aleister Crowley	[reply]
Re^2: what is the function should I need to use for trim white spaces ? by blazar (Canon) on Jan 12, 2006 at 11:00 UTC
`($_ = $before) =~ s/^\s+\|\s+$//g;` [download] Just as a minor nitpick I'd localise `$_`, but then I wouldn't bind with `=~`, I'd just `local $_ = $before; s/^\s+\|\s+$//g;` [download] or else `(my $after = $before) =~ s/^\s+\|\s+$//g;` [download]	[reply] [d/l] [select]


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