User login

To prevent automated spam submissions leave this field empty.

ack Linux Command Reference Example: ack command man page


ack - grep-like text finder


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

Ack is designed as a replacement for 99% of the uses of grep.

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.

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.

File Selection

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 selections, ack only searches files of types that it recognizes. If you have a file called foo.wango, and ack doesn't know what a .wango file is, ack won't search it.

The -a option tells ack to select all files, regardless of type.

Some files will never be selected by ack, even with -a, including:

Backup files: Files ending with ~, or #*#


Coredumps: Files matching core.\d+

However, ack always searches the files given on the command line, no matter what type. Furthermore, by specifying the -u option all files will be searched.
Directory Selection

ack descends through the directory tree of the starting directories specified. 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 --help.

When To Use Grep

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.


-a, --all

Operate on all files, regardless of type (but still skip directories like blib, CVS , etc.)
-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.
-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.
--color, --nocolor
--color highlights the matching text. --nocolor supresses the color. This is on by default unless the output is redirected, or running under Windows.
--env, --noenv
--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.
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.

--follow, --nofollow
Follow or don't follow symlinks, other than whatever starting files or directories were specified on the command line.
This is off by default.

Only paths matching REGEX are included in the search. The entire path and filename are matched against REGEX , and REGEX is a Perl regular expression, not a shell glob.
The options -i, -w, -v, and -Q do not apply to this REGEX .

Print files where the relative path + filename matches REGEX . This option is a convenience shortcut for -f -G REGEX .
The options -i, -w, -v, and -Q do not apply to this REGEX .

--group, --nogroup
--group groups matches by file name with. 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.
-h, --no-filename
Suppress the prefixing of filenames on output when multiple files are searched.
Print a short help statement.
-i, --ignore-case
Ignore case in the search strings.
This applies only to the PATTERN , not to the regexes given for the -g and -G options.

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).
--line= NUM
Only print line NUM of each file. Multiple lines can be given with multiple --line options or as a comma separated list (--line=3,5,7). --line=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.
--match REGEX
Specify the REGEX 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.
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)
Direct ack's output through program. This can also be specified via the "ACK_PAGER" environment variable.
Using --pager does not suppress grouping and coloring like piping output on the command-line does.

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.
This applies only to the PATTERN , not to the regexes given for the -g and -G options.

Specify a path to an alternate .ackrc file.
Sorts the found files lexically. Use this if you want your file listings to be deterministic between runs of ack.
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.
--type=TYPE, --type=noTYPE
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.

--type-add TYPE =.EXTENSION[,.EXT2[,...]]
Files with the given EXTENSION (s) are recognized as being of (the existing) type TYPE . See also "Defining your own types".
--type-set TYPE =.EXTENSION[,.EXT2[,...]]
Files with the given EXTENSION (s) are recognized as being of type TYPE . This replaces an existing definition for type TYPE . See also "Defining your own types".
-u, --unrestricted
All files and directories (including blib/, core.*, ...) are searched, nothing is skipped. When both -u and --ignore-dir are used, the --ignore-dir option has no effect.
-v, --invert-match
Invert match: select non-matching lines
This applies only to the PATTERN , not to the regexes given for the -g and -G options.

Display version and copyright information.
-w, --word-regexp
Force PATTERN to match only whole words. The PATTERN is wrapped with "\b" metacharacters.
This applies only to the PATTERN , not to the regexes given for the -g and -G options.

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.

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 filter

# 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.
ack looks in your home directory for the .ackrc. You can specify another location with the ACKRC variable, below.

If --noenv is specified on the command line, the .ackrc file is ignored.

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=.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=.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=.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=.c,.h and .xs files no longer belong to the type cc.

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


The types 'skipped', 'make', 'binary' and 'text' are considered "builtin" and cannot be altered.


The shebang line recognition of the types 'perl', 'ruby', 'php', 'python', 'shell' and 'xml' cannot be redefined by --type-set, it is always active. However, the shebang line is only examined for files where the extension is not recognised. Therefore it is possible to say ack --type-set perl=.perl --type-set,.pm,.pod,.t --perl --nofoo and only find your shiny new .perl files (and all files with unrecognized extension and perl on the shebang line).

Environment Variables


Specifies the location of the .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.

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

Note: The above environment variables are ignored if --noenv is specified on the command line.

Vim integration

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

set grepprg=ack\ -a
That examples uses "-a" to search through all files, but you may use other default flags. Now you can search with ack and easily step through the results in Vim:
:grep Dumper perllib


Andy Lester

by Susan White on Mon, 10/18/2010 - 09:19

Recent Posts


Are you excited for Avatar 2?:

Random image

Who doesn't want a pet frog?