[Discuss] GNU xargs trick

[mbr at arlsoft.com (MBR)]

Very cool!  I've used xargs for many years, but I never knew about the 
-I or -P options.  Are they only in the GNU implementation, or have they 
been ported to other platforms?

    Mark Rosenthal


On 4/27/16 10:25 AM, Rich Pieri wrote:
> There is a trick to GNU xargs that lets you easily parallelize
> processes. The particular use I discovered is for optimizing directories
> full of PNG files using optipng. I first looked at GNU parallel but it's
> way overkill for what I want. I found a couple of scripts that do some
> tricks with & and lock files but those ran into problems with
> complex-ish commands. Then I learned about the xargs trick:
>
> find . -name "*.png" -print | xargs -I{} -P 4 optipng -o1 -preserve {}
>
> The find part should be obvious, xargs maybe not so much. -I enables
> substitution. Whenever the string following -I appears it is replaced
> with the the line from stdin. -P 4 says to run a maximum of 4 processes;
> the default is 1. Everything after is the optipng command with {}
> replaced with each line from the find command.
>
> I dunnow if this has ever come up on the list but it's been quiet lately
> and I figured it's a cool enough trick to share.
>