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
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