Using grep is not cross-platform compatible, since -P/--perl-regexp is only available on GNU grep, not BSD grep.

Here is the solution using ripgrep:

$ rg -o "foobar (\w+)" -r '$1' <test.txt
bash
happy

As per man rg:

-r/--replace REPLACEMENT_TEXT Replace every match with the text given.

 

Capture group indices (e.g., $5) and names (e.g., $foo) are supported in the replacement string.

^{Related: GH-462.}

Using grep is not cross-platform compatible, since -P/--perl-regexp is only available on GNU grep, not BSD grep.

Here is the solution using ripgrep:

$ rg -o "foobar (\w+)" -r '$1' <test.txt
bash
happy

As per man rg:

-r/--replace REPLACEMENT_TEXT Replace every match with the text given.

Capture group indices (e.g., $5) and names (e.g., $foo) are supported in the replacement string.

^{Related: GH-462.}