Bash – Piping find results into another command

As other answers have already identified, ${f%.*} is expanded by the shell before it runs the xargs command. You need this expansion to happen once for each file name, with the shell variable f set to the file name (passing -I f doesn't do that: xargs has no notion of shell variable, it looks for the string f in the command, so if you'd used e.g. xargs -I e echo … it would have executed commands like ./somedir/somefile.wmacho .mp3).

Keeping on this approach, tell xargs to invoke a shell that can perform the expansion. Better, tell find — xargs is a largely obsolete tool and is hard to use correctly, as modern versions of find have a construct that does the same job (and more) with fewer plumbing difficulties. Instead of find … -print0 | xargs -0 command …, run find … -exec command … {} +.

find . -name '*.wma' -type f -exec sh -c 'for f; do echo "${f%.*}.mp3"; done' _ {} +

The argument _ is $0 in the shell; the file names are passed as the positional arguments which for f; do … loops over. A simpler version of this command executes a separate shell for each file, which is equivalent but slightly slower:

find . -name '*.wma' -type f -exec sh -c 'echo "${0%.*}.mp3"' {} \;

You don't actually need to use find here, assuming you're running a reasonably recent shell (ksh93, bash ≥4.0, or zsh). In bash, put shopt -s globstar in your .bashrc to activate the **/ glob pattern to recurse in subdirectories (in ksh, that's set -o globstar). Then you can run

for f in **/*.wma; do
  echo "${f%.*}.mp3"
done

(If you have directories called *.wma, add [ -f "$f" ] || continue at the beginning of the loop.)

Short answer:

If you just want to pass a bunch of lines as arguments to another command, xargs is your friend - in this case, because you're putting it into the middle of a command, you'll want to use the -I {} flag. This sets {} as a placeholder so that you can put wherever (you can set your own placeholder, but I usually stick to {} since it won't be mistaken for many other things.

Putting it all together (assuming the commands you've given do what you think they do!):

find server/lib -type f -exec basename {} \; | cut -f 1 -d '.' | xargs -I {} grep -R --exclude-dir=node_modules {} . -l

Long answer

Ok, so we can probably take this further. Let's say you wanted the format you mentioned earlier - you can xargs to sh -c so you can chain commands:

find server/lib -type f -exec basename {} \; | cut -f 1 -d '.' | xargs -I {} sh -c "echo {}; grep -R --exclude-dir=node_modules {} . -l"

Running this on my machine, it looks like this is giving you the files where the file is found. My brain is tired, so instead of wrapping it in a nice script (which is what you should actually do when oneliners start to get gnarly, and use https://www.shellcheck.net/ while you're at it) you can have this horrible hack instead, which (I think) will give you the output you're looking for:

find server/lib -type f -exec basename {} \; | cut -f 1 -d '.' | xargs -I {} sh -c "echo {}; grep -R --exclude-dir=node_modules {} . -l && printf \"\n\" || printf \"Not found\n\n\""