Chaining commands with xargs

Question

I am trying to accomplish the following result with bash:

1. grep files for some substring.
2. take the filenames (which can contain spaces) for these files and print them.
3. after printing each filename I want to grep again, however this time inside that file only.

So the result looks like this:

/tmp/file1.txt
it works!
/tmp/file2.txt
/tmp/file3.txt
it works!

I tried constructing a command like this:

grep -irl "something" . | xargs -I % sh -c 'echo "%"; cat "%" | grep -i "another thing" "%"'

Explanation: grep -l returns the filenames. Then I print those filenames with echo "%" and then I want to grep inside the file.

But no luck. What is the lesson here?

To clarify: My actual problem/goal is to find all files that contain a string A but do not contain a string B as well.

More clarification: I want something like grep A | grep -v B but I want a list of all files that matched A, as well.

Answer 1

What is the lesson here?

Probably do not over-egg the pudding.

% (
>   grep -l -r -- "$patternA" . |
>   tee /dev/fd/7 |
>   xargs grep -L -- "$patternB"
> ) 7>&1