Quickest, most efficient way to get number of files in dir?

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•Re: Quickest, most efficient way to get number of files in dir? by merlyn (Sage) on Mar 18, 2003 at 03:21 UTC
`opendir D, "somedir" or die; my $count = () = readdir D; $count -= 2; # :-) closedir D;` [download] Although you might benchmark that against this for both small and huge directories: `opendir D, "somedir" or die; my $count = -2; $count++ while readdir D; closedir D;` [download] -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l] [select]
Re: Quickest, most efficient way to get number of files in dir? by robartes (Priest) on Mar 18, 2003 at 07:36 UTC
Just a quick benchmark. I've used both of merlyn's variations on readdir and thrown in glob as well (just for giggles, as is shown in the benchmark results). Here's the code: `#!/usr/local/bin/perl -w use strict; use Benchmark qw(:all); my $dir="/home/bv/tmp/testdir"; cmpthese('1000', { 'merlyn_1' => \&merlyn1, 'merlyn_2' => \&merlyn2, 'glob' => \&glob, } ); sub merlyn1 { opendir D, $dir or die; my $count = () = readdir D; $count -= 2; # :-) closedir D; } sub merlyn2 { opendir D, $dir or die; my $count = -2; $count++ while readdir D; closedir D; } sub glob { my $count = () = glob ("$dir/"); $count += () = glob ("$dir/.[^.]"); $count-=2; }` [download] With 255 (empty) files, this is the result: `Benchmark: timing 1000 iterations of glob, merlyn_1, merlyn_2... glob: 6 wallclock secs ( 4.55 usr + 1.55 sys = 6.10 CPU) @ 16 +3.93/s (n=1000) merlyn_1: 1 wallclock secs ( 0.37 usr + 0.13 sys = 0.50 CPU) @ 20 +00.00/s (n=1000) merlyn_2: 1 wallclock secs ( 0.47 usr + 0.17 sys = 0.64 CPU) @ 15 +62.50/s (n=1000) Rate glob merlyn_2 merlyn_1 glob 164/s -- -90% -92% merlyn_2 1562/s 853% -- -22% merlyn_1 2000/s 1120% 28% --` [download] That's clear. Glob is very much out of the picture, while merlyn_1 is about a fifth to a quarter faster again than merlyn_2. Let's try 1024 files: `Rate glob merlyn_2 merlyn_1 glob 37.0/s -- -91% -93% merlyn_2 400/s 982% -- -22% merlyn_1 513/s 1287% 28% --` [download] Same result. merlyn_1 is the clear winner! I'm guessing that this is because we are not doing an increment to $count after every file, but that's just a wild guess. Update: For some extra giggles, here's the result for 10K files: `Rate glob merlyn_2 merlyn_1 glob 3.04/s -- -92% -93% merlyn_2 38.0/s 1150% -- -7% merlyn_1 40.7/s 1242% 7% --` [download] CU Robartes-	[reply] [d/l] [select]