I often have a command that processes one file, and I want to run it on every file in a directory. Is there any built-in way to do this?
For example, say I have a program data which outputs an important number about a file:
./data foo
137
./data bar
42
I want to run it on every file in the directory in some manner like this:
map data `ls *`
ls * | map data
to yield output like this:
foo: 137
bar: 42
If you just want to run a command on every file you can do this:
for i in *; do data "$i"; done
If you also wish to display the filename that it is currently working on then you could use this:
for i in *; do echo -n "$i: "; data "$i"; done
The common methods are:
ls * | while read file; do data "$file"; done
for file in *; do data "$file"; done
The second can run into problems if you have whitespace in filenames; in that case you'd probably want to make sure it runs in a subshell, and set IFS:
( IFS=$'\n'; for file in *; do data "$file"; done )
You can easily wrap the first one up in a script:
#!/bin/bash
# map.bash
while read file; do
"$1" "$file"
done
which can be executed as you requested - just be careful never to accidentally execute anything dumb with it. The benefit of using a looping construct is that you can easily place multiple commands inside it as part of a one-liner, unlike xargs where you'll have to place them in an executable script for it to run.
Of course, you can also just use the utility xargs:
find -maxdepth 0 * | xargs -n 1 data
Note that you should make sure indicators are turned off (ls --indicator-style=none) if you normally use them, or the @ appended to symlinks will turn them into nonexistent filenames.