Copy files using an input file to read file directions

Question

I'm using grep to search through 1 TB of files. I want to grep filenames and put the names in a text file AND I want to cp all files with a match to the dir /home/user/matches. I want to both tasks without searching through all my files with grep twice.

I had the idea to put filenames output into a text file with grep

grep -ril "xxx" . >> /home/user/matches/output-filename.txt

And now use output-filename.txt as input for cp and make cp execute line per line. How do I do that? awk? Or do you guys have other ideas to avoid searching through all files twice

Answer 1

File paths are sequences of bytes other than 0; they're not necessarily text let alone lines of texts. In particular, a file path

• may contain newline characters
• may contain sequences of bytes that don't form valid characters
• may be longer than LINE_MAX

The GNU implementation of grep (the one that added the -r option), can print the paths in a non-text format with -Z that is post-processable safely. For instance, GNU xargs can process that format with its -0 option:

xargs -r0 -a <(
  grep -rilZ xxx . |
   tee file.list
)  cp -it /home/user/matches --

(here also assuming GNU cp for its -t option)

If you want to print that list in a text¹ format that is understandable by a human, with GNU printf:

xargs -r0a file.list printf '%q\n'

---

^{¹ Well, it should ensure bytes that can't be decoded as characters are rendered as $'\234' representations. Same for control characters including newline, which is rendered as $'\n'. That addresses the first two points above, but it doesn't guarantee the output will have lines shorter than LINE_MAX (but then again, GNU implementations of standard text utilities generally don't have a limit on length of lines they support).}

Answer 2

You can use find with a chained pair of exec commands. Perhaps not the most efficient solution as it invokes grep for every file (and cp for every matched file), but it will work regardless of the characters in the file name:

mkdir -p ~/matches
find -type f -exec grep -il 'xxx' {} \; -exec cp -p {} ~/matches/ \; > ~/matches/output-filename.txt

Answer 3

Like this using tee, xargs commands (using NULL byte \0 as end of filename separator) and GNU grep:

Handle filenames with spaces, newlines etc...

mkdir -p ~/matches
grep -Zril "xxx" . |
    tee ~/matches/output-filename.txt |
    xargs -0 -I {} cp {} ~/matches/