UNIX for Dummies Questions & Answers

Hi!
I was looking for files to clean out, and I remembered reading somewhere that you could pipe the output of grep to rm. But I prefer to mv stuff to ~/.Trash/
I thought I'd try something like this:

Code:

ls  ~/Library/Preferences/ |grep '.*.\.iTunes\.plist\.[0-9].*' |xargs -J % mv % ~/.Trash/

I tried it a couple of different ways, but can't get it to work. I usually end up with the mv "usage" message. I was thinking that maybe mv wasn't receiving the full path, so I cd'ed to the source dir, but that didn't help.
Is there a way to pass grep's output to mv? Being a noob and an amateur, I'm a little leery of rm.

I'm using OS X (10.6.8) and bash.

Code:

ls  ~/Library/Preferences/*.iTunes.plist.[0-9].* |
while read fname
do
  mv $fname ~/.Trash/
done

Start with that. You can use filename matching to get what you want, skipping grep entirely.

Jim, forgive my ignorance, but I'm not sure what I'm looking at. I have no background with coding and I'm trying learn this stuff on my own.
This a shell script, not command line arguments, right?

The glob ~/Library/Preferences/*.iTunes.plist.[0-9].* expands to match all the files you want. The shell does this by the way -- not ls.

It uses ls to list the files you want. Then it uses read in a while loop to read them one by one, and each one it reads, causes it to run mv filename ~/.Trash/. When it runs out of lines to read, read will return false, and the loop will break.

That looks pretty redundant, though. How about

Code:

mv ~/Library/Preferences/*.iTunes.plist.[0-9].* ~/.Trash/

Yeah, that worked after I fixed up the search pattern a little. mv can't read a regex, (or the shell won't expand it), which is why I got grep involved, but as it happens I didn't need a regex. At least not for this group of files.

Code:

mv ~/Library/Preferences/*.iTunes.plist\.* ~/.Trash/

But it seems like, if you did need/desire to use a regex to locate files, there should be some way to pass that output to mv, no?

A generic Bourne shell won't do regexes. A new enough BASH can, but doesn't expand them into filenames the way it can do with globs. This is because of a fundamental difference between globs and regexes -- a regex only has to match part of a filename, but a glob always has to match an entire filename.

You can expand on Jim's code to do what you want. You're piping filenames into a while-read loop. Nothing stops you from shoving a grep in the way first. This is what makes text streams generic.

Code:

ls  ~/Library/Preferences/ | grep "regex" |
while read fname
do
  echo mv "$fname" ~/.Trash/
done

Remove the 'echo' once you've tested it and are sure it does what you want.

This is not as efficient as using a glob, though, since it runs mv 100 times to move 100 files, instead of once.

Globs have limits though. If you had millions of files, a glob probably couldn't handle them all, and you'd have to use straight ls or find with pipes...

I went to see what version of bash I had, and see that the noglob option is set. Could that be the problem?

noclobber off
noexec on
noglob on
nolog off
notify off
nounset off
onecmd off
physical off
pipefail off
posix off
privileged off
verbose off
vi off
xtrace off
bash-3.2$