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Revision as of 10:37, 5 September 2007 by Root (Talk | contribs) (exec versus xargs)

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exec versus xargs

You may notice that some people will pipe `find` output into `xargs`, but other people tell `find` to start a command using -exec. What is the difference? The difference is that xargs is faster. It will intelligently group arguments and feed batches to the subcommand, so it doesn't have to start a new instance of the subcommand for every argument.

Generally I find -exec easier to use because you can easily repeat the found filename in the exec argument. It's easier for me to express exactly what I want to be executed. Of course, some people think the `find` syntax is wacky. The `xargs` command comes in handy in other places such as a stream not generated by `find`, but when using `find` I stick with -exec unless I have a good reason not to.

You can always do it in a shell loop too:

  for filename in *.png ; do convert $filename `basename $filename .png`.jpg; done

Delete old files with find and cron

Put in /etc/cron.daily. This automatically deletes Spam older than 30 days from my Spam folder.

find /home/vpopmail/domains/ -type f -mtime +30 -exec rm -f {} \;

More CPU efficient:

find /home/vpopmail/domains/ -mtime +30 | xargs rm

List all extensions in the current directory

This came in handy when I was trying to find out exactly what mime-types I need to care about.

find . -print0 | xargs -L 1 -0 basename | sed -e "s/.*\(\\.\\s*\)/\\1/" | sort | uniq > /tmp/types

The -print0 option tells find to null-terminate filenames. The -0 option for xargs tells it to read null-terminated strings. These two options are used to handle filenames that have special characters such as quotes or line-feeds. If you don't do this then you may get the following error:

 xargs: unmatched single quote; by default quotes are special to xargs unless you use the -0 option