ack - grep-like text finder


    ack [options] PATTERN [FILE...]
    ack -f [options] [DIRECTORY...]


Ack is designed as an alternative to grep for programmers.

Ack searches the named input FILEs (or standard input if no files are named, or the file name - is given) for lines containing a match to the given PATTERN. By default, ack prints the matching lines.

PATTERN is a Perl regular expression. Perl regular expressions are commonly found in other programming languages, but for the particulars of their behavior, please consult perlreref. If you don't know how to use regular expression but are interested in learning, you may consult perlretut. If you do not need or want ack to use regular expressions, please see the -Q/--literal option.

Ack can also list files that would be searched, without actually searching them, to let you take advantage of ack's file-type filtering capabilities.


If files are not specified for searching, either on the command line or piped in with the -x option, ack delves into subdirectories selecting files for searching.

ack is intelligent about the files it searches. It knows about certain file types, based on both the extension on the file and, in some cases, the contents of the file. These selections can be made with the --type option.

With no file selection, ack searches through regular files that are not explicitly excluded by --ignore-dir and --ignore-file options, either present in ackrc files or on the command line.

The default options for ack ignore certain files and directories. These include:

Run ack with the --dump option to see what settings are set.

However, ack always searches the files given on the command line, no matter what type. If you tell ack to search in a coredump, it will search in a coredump.


ack descends through the directory tree of the starting directories specified. If no directories are specified, the current working directory is used. However, it will ignore the shadow directories used by many version control systems, and the build directories used by the Perl MakeMaker system. You may add or remove a directory from this list with the --[no]ignore-dir option. The option may be repeated to add/remove multiple directories from the ignore list.

For a complete list of directories that do not get searched, run ack --dump.


ack trumps grep as an everyday tool 99% of the time, but don't throw grep away, because there are times you'll still need it.

E.g., searching through huge files looking for regexes that can be expressed with grep syntax should be quicker with grep.

If your script or parent program uses grep --quiet or --silent or needs exit 2 on IO error, use grep.



Specifies an ackrc file to load after all others; see ACKRC LOCATION SEMANTICS.

-A NUM, --after-context=NUM

Print NUM lines of trailing context after matching lines.

-B NUM, --before-context=NUM

Print NUM lines of leading context before matching lines.


Print a break between results from different files. On by default when used interactively.

-C [NUM], --context[=NUM]

Print NUM lines (default 2) of context around matching lines.

-c, --count

Suppress normal output; instead print a count of matching lines for each input file. If -l is in effect, it will only show the number of lines for each file that has lines matching. Without -l, some line counts may be zeroes.

If combined with -h (--no-filename) ack outputs only one total count.

--[no]color, --[no]colour

--color highlights the matching text. --nocolor suppresses the color. This is on by default unless the output is redirected.

On Windows, this option is off by default unless the the Win32::Console::ANSI manpage module is installed or the ACK_PAGER_COLOR environment variable is used.


Sets the color to be used for filenames.


Sets the color to be used for matches.


Sets the color to be used for line numbers.


Show the column number of the first match. This is helpful for editors that can place your cursor at a given position.


Dumps the default ack options to standard output. This is useful for when you want to customize the defaults.


Writes the list of options loaded and where they came from to standard output. Handy for debugging.


--noenv disables all environment processing. No .ackrc is read and all environment variables are ignored. By default, ack considers .ackrc and settings in the environment.


--flush flushes output immediately. This is off by default unless ack is running interactively (when output goes to a pipe or file).


Only print the files that would be searched, without actually doing any searching. PATTERN must not be specified, or it will be taken as a path to search.


The list of files to be searched is specified in FILE. The list of files are separated by newlines. If FILE is -, the list is loaded from standard input.


Forces ack to act as if it were receiving input via a pipe.


Follow or don't follow symlinks, other than whatever starting files or directories were specified on the command line.

This is off by default.


Print files where the relative path + filename matches PATTERN. This option can be combined with --color to make it easier to spot the match.


--group groups matches by file name. This is the default when used interactively.

--nogroup prints one result per line, like grep. This is the default when output is redirected.

-H, --with-filename

Print the filename for each match. This is the default unless searching a single explicitly specified file.

-h, --no-filename

Suppress the prefixing of filenames on output when multiple files are searched.


Print a filename heading above each file's results. This is the default when used interactively.

--help, -?

Print a short help statement.

--help-types, --help=types

Print all known types.

-i, --ignore-case

Ignore case distinctions in PATTERN


Tells ack to completely ignore the default definitions provided with ack. This is useful in combination with --create-ackrc if you really want to customize ack.

--[no]ignore-dir=DIRNAME, --[no]ignore-directory=DIRNAME

Ignore directory (as CVS, .svn, etc are ignored). May be used multiple times to ignore multiple directories. For example, mason users may wish to include --ignore-dir=data. The --noignore-dir option allows users to search directories which would normally be ignored (perhaps to research the contents of .svn/props directories).

The DIRNAME must always be a simple directory name. Nested directories like foo/bar are NOT supported. You would need to specify --ignore-dir=foo and then no files from any foo directory are taken into account by ack unless given explicitly on the command line.


Ignore files matching FILTERTYPE:FILTERARGS. The filters are specified identically to file type filters as seen in Defining your own types.

-k, --known-types

Limit selected files to those with types that ack knows about. This is equivalent to the default behavior found in ack 1.


Only print line NUM of each file. Multiple lines can be given with multiple --lines options or as a comma separated list (--lines=3,5,7). --lines=4-7 also works. The lines are always output in ascending order, no matter the order given on the command line.

-l, --files-with-matches

Only print the filenames of matching files, instead of the matching text.

-L, --files-without-matches

Only print the filenames of files that do NOT match.

--match PATTERN

Specify the PATTERN explicitly. This is helpful if you don't want to put the regex as your first argument, e.g. when executing multiple searches over the same set of files.

    # search for foo and bar in given files
    ack file1 t/file* --match foo
    ack file1 t/file* --match bar
-m=NUM, --max-count=NUM

Stop reading a file after NUM matches.


Print this manual page.

-n, --no-recurse

No descending into subdirectories.


Show only the part of each line matching PATTERN (turns off text highlighting)


Output the evaluation of expr for each line (turns off text highlighting) If PATTERN matches more than once then a line is output for each non-overlapping match. For more information please see the section Examples of --output.

--pager=program, --nopager

--pager directs ack's output through program. This can also be specified via the ACK_PAGER and ACK_PAGER_COLOR environment variables.

Using --pager does not suppress grouping and coloring like piping output on the command-line does.

--nopager cancels any setting in ~/.ackrc, ACK_PAGER or ACK_PAGER_COLOR. No output will be sent through a pager.


Prints all lines, whether or not they match the expression. Highlighting will still work, though, so it can be used to highlight matches while still seeing the entire file, as in:

    # Watch a log file, and highlight a certain IP address
    $ tail -f ~/access.log | ack --passthru

Only works in conjunction with -f, -g, -l or -c (filename output). The filenames are output separated with a null byte instead of the usual newline. This is helpful when dealing with filenames that contain whitespace, e.g.

    # remove all files of type html
    ack -f --html --print0 | xargs -0 rm -f
-Q, --literal

Quote all metacharacters in PATTERN, it is treated as a literal.

-r, -R, --recurse

Recurse into sub-directories. This is the default and just here for compatibility with grep. You can also use it for turning --no-recurse off.


Suppress error messages about nonexistent or unreadable files. This is taken from fgrep.

--[no]smart-case, --no-smart-case

Ignore case in the search strings if PATTERN contains no uppercase characters. This is similar to smartcase in vim. This option is off by default, and ignored if -i is specified.

-i always overrides this option.


Sorts the found files lexicographically. Use this if you want your file listings to be deterministic between runs of ack.


Outputs the filetypes that ack associates with each file.

Works with -f and -g options.


Specify the types of files to include or exclude from a search. TYPE is a filetype, like perl or xml. --type=perl can also be specified as --perl, and --type=noperl can be done as --noperl.

If a file is of both type "foo" and "bar", specifying --foo and --nobar will exclude the file, because an exclusion takes precedence over an inclusion.

Type specifications can be repeated and are ORed together.

See ack --help=types for a list of valid types.


Files with the given FILTERARGS applied to the given FILTER are recognized as being of (the existing) type TYPE. See also Defining your own types.


Files with the given FILTERARGS applied to the given FILTER are recognized as being of type TYPE. This replaces an existing definition for type TYPE. See also Defining your own types.

--type-del TYPE

The filters associated with TYPE are removed from Ack, and are no longer considered for searches.

-v, --invert-match

Invert match: select non-matching lines


Display version and copyright information.

-w, --word-regexp

Force PATTERN to match only whole words. The PATTERN is wrapped with \b metacharacters.


An abbreviation for --files-from=-; the list of files to search are read from standard input, with one line per file.


Stops after reporting first match of any kind. This is different from --max-count=1 or -m1, where only one match per file is shown. Also, -1 works with -f and -g, where -m does not.


Display the all-important Bill The Cat logo. Note that the exact spelling of --thpppppt is not important. It's checked against a regular expression.


Check with the admiral for traps.


Chocolate, Chocolate, Chocolate!

THE .ackrc FILE

The .ackrc file contains command-line options that are prepended to the command line before processing. Multiple options may live on multiple lines. Lines beginning with a # are ignored. A .ackrc might look like this:

    # Always sort the files
    # Always color, even if piping to a another program
    # Use "less -r" as my pager
    --pager=less -r

Note that arguments with spaces in them do not need to be quoted, as they are not interpreted by the shell. Basically, each line in the .ackrc file is interpreted as one element of @ARGV.

ack looks in several locations for .ackrc files; the searching process is detailed in ACKRC LOCATION SEMANTICS. These files are not considered if --noenv is specified on the command line.

Defining your own types

ack allows you to define your own types in addition to the predefined types. This is done with command line options that are best put into an .ackrc file - then you do not have to define your types over and over again. In the following examples the options will always be shown on one command line so that they can be easily copy & pasted.

ack --perl foo searches for foo in all perl files. ack --help=types tells you, that perl files are files ending in .pl, .pm, .pod or .t. So what if you would like to include .xs files as well when searching for --perl files? ack --type-add perl:ext:xs --perl foo does this for you. --type-add appends additional extensions to an existing type.

If you want to define a new type, or completely redefine an existing type, then use --type-set. ack --type-set eiffel:ext:e,eiffel defines the type eiffel to include files with the extensions .e or .eiffel. So to search for all eiffel files containing the word Bertrand use ack --type-set eiffel:ext:e,eiffel --eiffel Bertrand. As usual, you can also write --type=eiffel instead of --eiffel. Negation also works, so --noeiffel excludes all eiffel files from a search. Redefining also works: ack --type-set cc:ext:c,h and .xs files no longer belong to the type cc.

When defining your own types in the .ackrc file you have to use the following:


or writing on separate lines


The following does NOT work in the .ackrc file:

  --type-set eiffel:ext:e,eiffel

In order to see all currently defined types, use --help-types, e.g. ack --type-set backup:ext:bak --type-add perl:ext:perl --help-types

In addition to filtering based on extension (like ack 1.x allowed), ack 2 offers additional filter types. The generic syntax is --type-set TYPE:FILTER:FILTERARGS; FILTERARGS depends on the value of FILTER.


is filters match the target filename exactly. It takes exactly one argument, which is the name of the file to match.


    --type-set make:is:Makefile

ext filters match the extension of the target file against a list of extensions. No leading dot is needed for the extensions.


    --type-set perl:ext:pl,pm,t

match filters match the target filename against a regular expression. The regular expression is made case insensitive for the search.


    --type-set make:match:/(gnu)?makefile/

firstlinematch matches the first line of the target file against a regular expression. Like match, the regular expression is made case insensitive.


    --type-add perl:firstlinematch:/perl/

More filter types may be made available in the future.


For commonly-used ack options, environment variables can make life much easier. These variables are ignored if --noenv is specified on the command line.


Specifies the location of the user's .ackrc file. If this file doesn't exist, ack looks in the default location.


This variable specifies default options to be placed in front of any explicit options on the command line.


Specifies the color of the filename when it's printed in --group mode. By default, it's "bold green".

The recognized attributes are clear, reset, dark, bold, underline, underscore, blink, reverse, concealed black, red, green, yellow, blue, magenta, on_black, on_red, on_green, on_yellow, on_blue, on_magenta, on_cyan, and on_white. Case is not significant. Underline and underscore are equivalent, as are clear and reset. The color alone sets the foreground color, and on_color sets the background color.

This option can also be set with --color-filename.


Specifies the color of the matching text when printed in --color mode. By default, it's "black on_yellow".

This option can also be set with --color-match.

See ACK_COLOR_FILENAME for the color specifications.


Specifies the color of the line number when printed in --color mode. By default, it's "bold yellow".

This option can also be set with --color-lineno.

See ACK_COLOR_FILENAME for the color specifications.


Specifies a pager program, such as more, less or most, to which ack will send its output.

Using ACK_PAGER does not suppress grouping and coloring like piping output on the command-line does, except that on Windows ack will assume that ACK_PAGER does not support color.

ACK_PAGER_COLOR overrides ACK_PAGER if both are specified.


Specifies a pager program that understands ANSI color sequences. Using ACK_PAGER_COLOR does not suppress grouping and coloring like piping output on the command-line does.

If you are not on Windows, you never need to use ACK_PAGER_COLOR.


ack uses the colors available in Perl's the Term::ANSIColor manpage module, which provides the following listed values. Note that case does not matter when using these values.

Foreground colors

    black  red  green  yellow  blue  magenta  cyan  white
    bright_black  bright_red      bright_green  bright_yellow
    bright_blue   bright_magenta  bright_cyan   bright_white

Background colors

    on_black  on_red      on_green  on_yellow
    on_blue   on_magenta  on_cyan   on_white
    on_bright_black  on_bright_red      on_bright_green  on_bright_yellow
    on_bright_blue   on_bright_magenta  on_bright_cyan   on_bright_white


Vim integration

ack integrates easily with the Vim text editor. Set this in your .vimrc to use ack instead of grep:

    set grepprg=ack\ -k

That example uses -k to search through only files of the types ack knows about, but you may use other default flags. Now you can search with ack and easily step through the results in Vim:

  :grep Dumper perllib

Miles Sterrett has written a Vim plugin for ack which allows you to use :Ack instead of :grep, as well as several other advanced features.

Emacs integration

Phil Jackson put together an ack.el extension that "provides a simple compilation mode ... has the ability to guess what files you want to search for based on the major-mode."

TextMate integration

Pedro Melo is a TextMate user who writes "I spend my day mostly inside TextMate, and the built-in find-in-project sucks with large projects. So I hacked a TextMate command that was using find + grep to use ack. The result is the Search in Project with ack, and you can find it here:"

Shell and Return Code

For greater compatibility with grep, ack in normal use returns shell return or exit code of 0 only if something is found and 1 if no match is found.

(Shell exit code 1 is $?=256 in perl with system or backticks.)

The grep code 2 for errors is not used.

If -f or -g are specified, then 0 is returned if at least one file is found. If no files are found, then 1 is returned.


If ack gives you output you're not expecting, start with a few simple steps.

Use --noenv

Your environment variables and .ackrc may be doing things you're not expecting, or forgotten you specified. Use --noenv to ignore your environment and .ackrc.

Use -f to see what files have been selected

Ack's -f was originally added as a debugging tool. If ack is not finding matches you think it should find, run ack -f to see what files have been selected. You can also add the --show-types options to show the type of each file selected.

Use --dump

This lists the ackrc files that are loaded and the options loaded from them. So for example you can find a list of directories that do not get searched or where filetypes are defined.


Use the .ackrc file.

The .ackrc is the place to put all your options you use most of the time but don't want to remember. Put all your --type-add and --type-set definitions in it. If you like --smart-case, set it there, too. I also set --sort-files there.

Use -f for working with big codesets

Ack does more than search files. ack -f --perl will create a list of all the Perl files in a tree, ideal for sending into xargs. For example:

    # Change all "this" to "that" in all Perl files in a tree.
    ack -f --perl | xargs perl -p -i -e's/this/that/g'

or if you prefer:

    perl -p -i -e's/this/that/g' $(ack -f --perl)

Use -Q when in doubt about metacharacters

If you're searching for something with a regular expression metacharacter, most often a period in a filename or IP address, add the -Q to avoid false positives without all the backslashing. See the following example for more...

Use ack to watch log files

Here's one I used the other day to find trouble spots for a website visitor. The user had a problem loading troublesome.gif, so I took the access log and scanned it with ack twice.

    ack -Q /path/to/access.log | ack -Q -B5 troublesome.gif

The first ack finds only the lines in the Apache log for the given IP. The second finds the match on my troublesome GIF, and shows the previous five lines from the log in each case.

Examples of --output

Following variables are useful in the expansion string:


The whole string matched by PATTERN.

$1, $2, ...

The contents of the 1st, 2nd ... bracketed group in PATTERN.


The string before the match.


The string after the match.

For more details and other variables see perlvar.

This example shows how to add text around a particular pattern (in this case adding _ around word with "e") "\w*e\w*" quick.txt --output="$`_$&_$'"
    _The_ quick brown fox jumps over the lazy dog
    The quick brown fox jumps _over_ the lazy dog
    The quick brown fox jumps over _the_ lazy dog

This shows how to pick out particular parts of a match using ( ) within regular expression.

  ack '=head(\d+)\s+(.*)' --output=' $1 : $2'
  input file contains "=head1 NAME"
  output  "1 : NAME"

Share your knowledge

Join the ack-users mailing list. Send me your tips and I may add them here.


Why isn't ack finding a match in (some file)?

Probably because it's of a type that ack doesn't recognize. ack's searching behavior is driven by filetype. If ack doesn't know what kind of file it is, ack ignores the file.

Use the -f switch to see a list of files that ack will search for you. You can use the --show-types switch to show which type ack thinks each file is.

Wouldn't it be great if ack did search & replace?

No, ack will always be read-only. Perl has a perfectly good way to do search & replace in files, using the -i, -p and -n switches.

You can certainly use ack to select your files to update. For example, to change all "foo" to "bar" in all PHP files, you can do this from the Unix shell:

    $ perl -i -p -e's/foo/bar/g' $(ack -f --php)

Can I make ack recognize .xyz files?

Yes! Please see Defining your own types. If you think that ack should recognize a type by default, please see ENHANCEMENTS.

There's already a program/package called ack.

Yes, I know.

Why is it called ack if it's called ack-grep?

The name of the program is "ack". Some packagers have called it "ack-grep" when creating packages because there's already a package out there called "ack" that has nothing to do with this ack.

I suggest you make a symlink named ack that points to ack-grep because one of the crucial benefits of ack is having a name that's so short and simple to type.

To do that, run this with sudo or as root:

   ln -s /usr/bin/ack-grep /usr/bin/ack

Alternatively, you could use a shell alias:

    # bash/zsh
    alias ack=ack-grep
    # csh
    alias ack ack-grep

What does ack mean?

Nothing. I wanted a name that was easy to type and that you could pronounce as a single syllable.

Can I do multi-line regexes?

No, ack does not support regexes that match multiple lines. Doing so would require reading in the entire file at a time.

If you want to see lines near your match, use the --A, --B and --C switches for displaying context.

Why is ack telling me I have an invalid option when searching for +foo?

ack treats command line options beginning with + or - as options; if you would like to search for these, you may prefix your search term with -- or use the --match option. (However, don't forget that + is a regular expression metacharacter!)

Why does "ack '.{40000,}'" fail? Isn't that a valid regex?

The Perl language limits the repetition quanitifier to 32K. You can search for .{32767} but not .{32768}.


Ack can load its configuration from many sources. This list specifies the sources Ack looks for configuration; each one that is found is loaded in the order specified here, and each one overrides options set in any of the sources preceding it. (For example, if I set --sort-files in my user ackrc, and --nosort-files on the command line, the command line takes precedence)


A lot of changes were made for ack 2; here is a list of them.






Andy Lester, <andy at>


Please report any bugs or feature requests to the issues list at Github:


All enhancement requests MUST first be posted to the ack-users mailing list at I will not consider a request without it first getting seen by other ack users. This includes requests for new filetypes.

There is a list of enhancements I want to make to ack in the ack issues list at Github:

Patches are always welcome, but patches with tests get the most attention.


Support for and information about ack can be found at:


How appropriate to have acknowledgements!

Thanks to everyone who has contributed to ack in any way, including Stephen Thirlwall, Jonah Bishop, Chris Rebert, Denis Howe, Raúl Gundín, James McCoy, Daniel Perrett, Steven Lee, Jonathan Perret, Fraser Tweedale, Raál Gundán, Steffen Jaeckel, Stephan Hohe, Michael Beijen, Alexandr Ciornii, Christian Walde, Charles Lee, Joe McMahon, John Warwick, David Steinbrunner, Kara Martens, Volodymyr Medvid, Ron Savage, Konrad Borowski, Dale Sedivic, Michael McClimon, Andrew Black, Ralph Bodenner, Shaun Patterson, Ryan Olson, Shlomi Fish, Karen Etheridge, Olivier Mengue, Matthew Wild, Scott Kyle, Nick Hooey, Bo Borgerson, Mark Szymanski, Marq Schneider, Packy Anderson, JR Boyens, Dan Sully, Ryan Niebur, Kent Fredric, Mike Morearty, Ingmar Vanhassel, Eric Van Dewoestine, Sitaram Chamarty, Adam James, Richard Carlsson, Pedro Melo, AJ Schuster, Phil Jackson, Michael Schwern, Jan Dubois, Christopher J. Madsen, Matthew Wickline, David Dyck, Jason Porritt, Jjgod Jiang, Thomas Klausner, Uri Guttman, Peter Lewis, Kevin Riggle, Ori Avtalion, Torsten Blix, Nigel Metheringham, Gábor Szabó, Tod Hagan, Michael Hendricks, Ævar Arnfjörð Bjarmason, Piers Cawley, Stephen Steneker, Elias Lutfallah, Mark Leighton Fisher, Matt Diephouse, Christian Jaeger, Bill Sully, Bill Ricker, David Golden, Nilson Santos F. Jr, Elliot Shank, Merijn Broeren, Uwe Voelker, Rick Scott, Ask Bjørn Hansen, Jerry Gay, Will Coleda, Mike O'Regan, Slaven Rezić, Mark Stosberg, David Alan Pisoni, Adriano Ferreira, James Keenan, Leland Johnson, Ricardo Signes, Pete Krawczyk and Rob Hoelz.


Copyright 2005-2014 Andy Lester.

This program is free software; you can redistribute it and/or modify it under the terms of the Artistic License v2.0.

See or the file that comes with the ack distribution.