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: 

$ time ls /long/path/to/bigdir | wc -l
  101645

real    0m0.463s
user    0m0.421s
sys     0m0.078s

$ time perl -e 'opendir(D,"/long/path/to/bigdir");
 @f=readdir D; print "$_\n" for (@f)' | wc -l
  101647

real    0m0.156s
user    0m0.124s
sys     0m0.070s

[download]
(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".

In reply to Re^2: Automatically distributing and finding files in subdirectories by graff
in thread Automatically distributing and finding files in subdirectories by myuserid7

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