bash "map" equivalent: run command on each file [duplicate]

Question

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

Answer 1

If you are just trying to execute your data program on a bunch of files, the easiest/least complicated way is to use -exec in find.

Say you wanted to execute data on all txt files in the current directory (and subdirectories). This is all you'd need:

find . -name "*.txt" -exec data {} \;

If you wanted to restrict it to the current directory, you could do this:

find . -maxdepth 1 -name "*.txt" -exec data {} \;

There are lots of options with find.

Answer 2

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

Answer 3

It looks like you want xargs:

find . --maxdepth 1 | xargs -d'\n' data

To print each command first, it gets a little more complex:

find . --maxdepth 1 | xargs -d'\n' -I {} bash -c "echo {}; data {}"