Many old Unix hands will be _very_ familiar with the process of building up a
pipeline...
For example find all corrupted bz2 packages in a directory....
find /var/apt-cacher -name '*.bz2' | xargs bunzip2 -tv
Or finding an email in your archives....
find ~/oldmail -type f | xargs zgrep -i 'some keyphrase'
..to give two very simple very standard sorts of examples...
Now, if you have a dual core (like me) or higher processor... watch
what happens to your CPU load with something like gkrellm.
Only one core is doing all the work.
The man page says...
--max-procs=max-procs, -P max-procs
Run up to max-procs processes at a time; the default is 1. If
max-procs is 0, xargs will run
as many processes as possible at a time.
Well, lets make things happen twice as fast....
find ~/oldmail -type f | xargs -P 2 zgrep -i 'some keyphrase'
Whoops... That didn't work. Still only keeping one core busy.
Lets see what happen...
find ~/oldmail -type f | xargs -P 2 echo ---------MARKER----------- zgrep -i
'some keyphrase'
---------MARKER----------- zgrep -i 'some keyphrase' file.1 file.2 file.3
.......
Aha! xargs packed _all_ the files onto the command line of one zgrep
instance, it didn't need to invoke a second.
In fact, if only I had finished reading the man page...
Use the -n option with -P; otherwise chances are that only one exec will
be done.
I would have known that!
Let's try that again...
find ~/oldmail -type f | xargs -P 2 -n 1 zgrep -i 'some keyphrase'
Hmm. That's creating hundreds of setups and tear downs for zgrep. How about...
find ~/oldmail -type f | xargs -P 2 -n 5 zgrep -i 'some keyphrase'
Yip. Good balance. Both cores busy full time on useful work.
John Carter Phone : (64)(3) 358 6639
Tait Electronics Fax : (64)(3) 359 4632
PO Box 1645 Christchurch Email : [EMAIL PROTECTED]
New Zealand
