|Perl Monk, Perl Meditation|
Re^2: Automatically distributing and finding files in subdirectoriesby graff (Chancellor)
|on Jul 18, 2006 at 03:13 UTC||Need Help??|
This is a case where it's a good idea to use the shell, which is well optimized...
Not really. I've done a simple benchmark on a pretty big directory, and running a perl one-liner with opendir/readdir compares favorably to running "ls".
In addition, using perl's built-in "rename" function on a long list of files in order to relocate them within a directory tree will certainly be faster that running "mv" repeatedly in any kind of script, because with perl, you have one process making lots of calls to an OS-level library function, whereas each "mv" command is a separate process being started and shut down.
Here's my simple-minded benchmark for two ways of listing files in a directory, on a path I happened to find in my local nfs space with over 100 K files:
(The two extra files found by perl are "." and "..", of course. When I change it to @f=grep/\w/,readdir D to get the same list as "ls", the perl one-liner still shows up as faster. Go figure.)
I ran those a few times each, varying the order of the two command lines to eliminate OS caching as a factor, and the results shown above were consistent. This was actually kind of surprising to me, because I always thought that basic "ls" on a directory was pretty quick ("ls -l" is a lot slower, and there's no point using the "-l" option in the OP's case).
Note that the results would be seriously reversed if the perl script used File::Find instead of opendir/readdir.
In terms of ease and flexibility of scripting, ease of reading the resulting script, and overall speed of execution, I believe pure Perl wins over the shell for cases like this.
UPDATE: Thanks to a comment from Hue-Bond, I see now that there was a flaw in my benchmark: "ls" sorts its output by default. If I run it as "ls -U" to skip the sort, it wins easily over the perl one-liner. It's interesting that if I add "sort" to the perl script, to make it match the default "ls" output, it's still faster than "ls".