How to grep and execute a command (for every match)

Question

How to grep in one file and execute for every match a command?

File:

foo
bar
42
foo
bar

I want to execute to execute for example

Answer 1

There is an interesting command in linux for that: xargs, It allows You to use the output from previous command(grep, ls, find, etc.) as the input for a custom execution but with several options that allows You to even execute the custom command in parallel. Below some examples:

Based in your question, here is how to print the date with format "%s.%N" for each "foo" match in file.txt:

grep "foo" file.txt | xargs -I {} date +%s.%N

A more interesting use is creating a file for each match, but in this case if matches are identical the file will be override:

grep "foo" file.txt | xargs -I {} touch {}

If You want to concatenate a custom date to the file created

grep "foo" file.txt | xargs -I {} touch "{}`date +%s.%N`"

Imagine the matches are file names and You want to make a backup of them:

grep "foo" file.txt | xargs -I {} cp {} "{}.backup"

And finally for xargs using the custom date in the backupName

grep "foo" file.txt | xargs -I {} cp {} "{}`date +%s.%N`"

For more info about options like parallel execution of xargs visit: https://en.wikipedia.org/wiki/Xargs and for date formats: https://www.thegeekstuff.com/2013/05/date-command-examples/

Extra I have found also a normal for command useful in this scenarios It is simpler but less versatile below are the equivalent for above examples:

for i in `grep "foo" test.txt`; do date +%s.%N; done
for i in `grep "foo" test.txt`; do touch ${i}; done
for i in `grep "foo" test.txt`; do touch "${i}`date +%s.%N`"; done
for i in `grep "foo" test.txt`; do cp ${i} "${i}.backup2"; done
for i in `grep "foo" test.txt`; do cp ${i} "${i}.backup2`date +%s.%N`"; done

Have Fun!!!