ack — A search tool like `grep`, optimized for developers. See also: `rg`.
# source: tldr · verified

Examples:
  # Search for files containing a string or `regex` in the current directory recursively
    $ ack "search_pattern"
  # Search for a case-insensitive pattern
    $ ack [-i|--ignore-case] "search_pattern"
  # Search for lines matching a pattern, printing only the matched text and not the rest of the line
    $ ack [-o|--output '$&'] "search_pattern"

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