grep: Recursive Search

So far grep searched one file. But what if you do not know which file contains the word, only that it is somewhere in a folder full of files and sub-folders?

The -r option (recursive) tells grep to search every file in a whole directory tree.

grep -r "sector 7" logs

logs/january.log:Mission to sector 7 approved.
logs/old/archive.log:Sector 7 survey complete.

Notice the output now starts with the file name of each match, then a colon, then the matching line. That way you know where every hit came from.

Searching from the current folder

A single dot . means "the current directory". To search everything under where you stand:

grep -r "error" .

Combine with other options

Recursive search works with the options you already know:

grep -ri "error" logs     # recursive + case-insensitive
grep -rn "error" logs     # recursive + line numbers

grep -r is how you answer "is this word mentioned anywhere in my project?".

Mission: Failure Investigation

A recurring malfunction has been reported and the maintenance team needs every mention of failure from the station logs, plus the offending file pulled out for evidence. The logs folder contains files spread across several sub-folders.

1. Search recursively for failure everywhere under the logs folder. Each hit shows which file it came from.
2. Create a folder called investigation and copy the January log logs/january.log, which holds the coolant-pump failure, into it as evidence.log.
3. Display the evidence file to confirm it captured the failure line.

Expected result

Every failure line appears with its file path, and the investigation folder holds a copy of the January log as evidence.log.