ack

Search files for a pattern

TLDR

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]"

Limit search to files of a specific type

$ ack [[-t|--type]] [ruby] "[search_pattern]"

Do not search in files of a specific type

$ ack [[-t|--type]] no[ruby] "[search_pattern]"

Count the total number of matches found

$ ack [[-c|--count]] [[-h|--no-filename]] "[search_pattern]"

Print the file names and the number of matches for each file only

$ ack [[-c|--count]] [[-l|--files-with-matches]] "[search_pattern]"

List all the values that can be used with --type

$ ack --help-types

SYNOPSIS

ack [options] <PATTERN> [<FILE> ...]

-i, --ignore-case
    Ignore case distinctions in PATTERN

-w, --word
    Search for PATTERN only as a whole word

-l, --files-with-matches
    Only print filenames containing matches

-L, --files-without-matches
    Only print filenames not containing matches

--type=TYPE
    Operate on files of TYPE (e.g., --type=perl, --type=js)

--ignore-dir=DIR
    Ignore directory DIR

-a, --all
    Include all text files, even those without explicit type

-c, --count
    Count matching lines per file

-f
    Read list of files to search from stdin or args

-g PATTERN
    Find files matching PATTERN

--color
    Colorize matches (on|off|always)

-A NUM, --after-context=NUM
    Print NUM lines of trailing context

-B NUM, --before-context=NUM
    Print NUM lines of leading context

-C NUM, --context=NUM
    Print NUM lines of context before/after

DESCRIPTION

Ack is a powerful, grep-inspired command-line tool designed specifically for searching large codebases and text files. Unlike traditional grep, ack intelligently skips binary files, version control directories (like .git, .svn), and common build directories (e.g., blib, _build) by default, making it faster and more efficient for developers.

It supports Perl-compatible regular expressions (PCRE), colorized output for matches, and file type filtering (e.g., --perl, --js) based on extensions and shebangs. Ack highlights matches in context with line numbers, handles recursion across directories, and provides options for ignoring case, inverting matches, or showing only filenames with hits.

Ideal for programmers, ack reduces noise in search results, speeds up workflows in projects with thousands of files, and integrates well with editors like Vim and Emacs. It's written in Perl, portable across Unix-like systems, and available as 'ack-grep' in some distros to avoid conflicts with BSD ack.

CAVEATS

Ack is not installed by default on most systems; install via package manager (e.g., apt install ack). Some distros rename it to ack-grep. Limited to Perl regex; newer tools like ripgrep may be faster.

FILE TYPES

Ack defines 50+ filetypes like --python, --html. List with ack --help=types; override with --type-set.

EXAMPLES

ack --perl 'TODO' searches TODO in Perl files.
ack -i error . case-insensitive search for 'error' recursively.
ack --print0 | xargs -0 grep foo pipes nul-separated filenames.

HISTORY

Developed by Andy Lester in 2007 as 'ack' ("better grep") to address grep's shortcomings for code searching. Written in Perl, it evolved through versions: ack 1.x (2008-2010), ack 2.x (2010-2014) with improved filetypes, and ack 3.x (2014+) adding --known-types and bug fixes. Widely adopted by developers; maintained on GitHub.

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