Grep
From wikinotes
Search file contents.
Documentation
man grep https://manpages.debian.org/buster/grep/grep.1.en.html
Usage
grep <dir> \ -C3 `# show 3x lines before/after each match` \ -l `# show only matched files` \ -i `# case insensitive search` \ -v `# lines-not matching` \ -E `# extended regex` \multiline grep
grep -Pzo 'def[^\n]+\n\tfoo'