How to apply shell command to each line of a command output?

Question

Suppose I have some output from a command (such as ls -1):

a
b
c
d
e
...

I want to apply a command (say echo) to each one, in turn. E.g.

echo a
echo b
echo c
echo d
echo e
...

What's the easiest way to do that in bash?

Answer 1

You can use a for loop:

for file in * ; do
   echo "$file"
done

Note that if the command in question accepts multiple arguments, then using xargs is almost always more efficient as it only has to spawn the utility in question once instead of multiple times.

Answer 2

You can use a basic prepend operation on each line:

ls -1 | while read line ; do echo echo $line ; done

Or you can pipe the output to sed for more complex operations:

ls -1 | sed 's/^\(.*\)$/echo \1/'

Answer 3

It's probably easiest to use xargs. In your case:

ls -1 | xargs -L1 echo

Answer 4

for s in `cmd`; do echo $s; done

If cmd has a large output:

cmd | xargs -L1 echo

Answer 5

BASH FAQ entry #1

BASH Pitfalls entry #1