Re: Grabbing file prefixes with Reg Exp

Allow me to point out some places of improvement:

to see if a string ends in something, you must anchor it with \z, \Z, or $
match what you need; this is wasteful: /.*\.foo$/
using /i is sometimes wasteful, especially for a few characters

That said, I offer:

my @files = map s/\.[Rr][Aa][Mm]$// ? $_ : (), readdir DH;
[download]

Maybe you think those character classes look ugly, and maybe the difference is minimal, but in a case like this, I think it's a wise investment. Also, you may wish to use a different ending anchor in place of $.

japhy -- Perl and Regex Hacker

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Re: Re: Grabbing file prefixes with Reg Exp by dws (Chancellor) on May 14, 2001 at 00:03 UTC
using /i is sometimes wasteful, especially for a few characters <counteropinion> Unless the regexp is going to be in a performance-sensitive area of code, the performance gained by using character classes instead of /i is going to be outweighed by the readability hit. To my eye, it's easier (albeit only slightly so) to grasp the intent of `my @files = map s/\.ram$//i ? $_ : (), readdir DH;` than it is to grasp `my @files = map s/\.[Rr][Aa][Mm]$// ? $_ : (), readdir DH;` When hardware performance isn't an issue, optimize for wetware (readability).	[reply] [d/l] [select]
Re: Re: Grabbing file prefixes with Reg Exp by MeowChow (Vicar) on May 14, 2001 at 02:18 UTC
Didn't you mean to make this a `grep`? :) `my @files = grep s/\.ram$//i , readdir DH;` [download] Also, I agree with dws regarding the readability of the character classes, and believe you're altogether mistaken regarding the performance issue: `use strict; use Benchmark qw(cmpthese); my $strorig = 'yabadabadooo this bud is a buda fora youa'; cmpthese (-3, { mod => sub { my $str = $strorig; $str =~ m/.BUD./i }, class => sub { my $str = $strorig; $str =~ m/.[Bb][Uu][Dd]./ }, }); ## Results (under ActiveState 5.6) ## Rate class mod class 347719/s -- -15% mod 408606/s 18% --` [download] MeowChow s aamecha.s a..a\u$&owag.print	[reply] [d/l] [select]
Re: Re: Re: Grabbing file prefixes with Reg Exp by japhy (Canon) on May 14, 2001 at 02:47 UTC
Yes, it was meant to be a `grep()` -- I took the `map()` and modified it, and forgot to change it. And I guess I'm mistaken about char classes. I was using information from MRE, I think, which is now oldish, so Perl has probably made some changes. `japhy` -- Perl and Regex Hacker	[reply]