ACK

Section: User Contributed Perl Documentation (1)
Updated: 2012-01-12
Index

NAME

ack - grep-like text finder

SYNOPSIS

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

DESCRIPTION

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 arenamed, or the file name - is given) for lines containing a match to thegiven PATTERN. By default, ack prints the matching lines.

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

FILE SELECTION

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

With no file selections, ack only searches files of types thatit recognizes. If you have a file called foo.wango, and ackdoesn't know what a .wango file is, ack won't search it.

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

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

•: Backup files: Files matching #*# or ending with ~.
•: 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 allfiles will be searched.

DIRECTORY SELECTION

ack descends through the directory tree of the starting directoriesspecified. However, it will ignore the shadow directories used bymany version control systems, and the build directories used by thePerl MakeMaker system. You may add or remove a directory from thislist with the --[no]ignore-dir option. The option may be repeatedto add/remove multiple directories from the ignore list.

For a complete list of directories that do not get searched, runack --help.

WHEN TO USE GREP

ack trumps grep as an everyday tool 99% of the time, but don'tthrow grep away, because there are times you'll still need it.

E.g., searching through huge files looking for regexes that can beexpressed 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.

OPTIONS

-a, --all

Operate on all files, regardless of type (but still skip directorieslike 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 foreach input file. If -l is in effect, it will only show thenumber 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.

--color, --nocolor

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

On Windows, this option is off by default unless theWin32::Console::ANSI module is installed or the "ACK_PAGER_COLOR"environment variable is used.

--color-filename=color

Sets the color to be used for filenames.

--color-match=color

Sets the color to be used for matches.

--color-lineno=color

Sets the color to be used for line numbers.

--column

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

--env, --noenv

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

--flush

--flush flushes output immediately. This is off by defaultunless ack is running interactively (when output goes to a pipeor file).

-f

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

--follow, --nofollow

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

This is off by default.

-G REGEX

Only paths matching REGEX are included in the search. The entirepath and filename are matched against REGEX, and REGEX is aPerl regular expression, not a shell glob.

The options -i, -w, -v, and -Q do not apply to this REGEX.

-g REGEX

Print files where the relative path + filename matches REGEX. This option isa 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 whenused interactively.

--nogroup prints one result per line, like grep. This is the defaultwhen 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 aresearched.

--help

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 -gand -G options.

--[no]ignore-dir=DIRNAME

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

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

--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=4-7also works. The lines are always output in ascending order, no matter theorder 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. This is equivalentto specifying -l and -v.

--match REGEX

Specify the REGEX explicitly. This is helpful if you don't want to put theregex as your first argument, e.g. when executing multiple searches over thesame 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.

--man

Print this manual page.

-n, --no-recurse

No descending into subdirectories.

-o

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

--output=expr

Output the evaluation of expr for each line (turns off texthighlighting)

--pager=program

Direct ack's output through program. This can also be specifiedvia the "ACK_PAGER" and "ACK_PAGER_COLOR" environment variables.

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

--passthru

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

    # Watch a log file, and highlight a certain IP address    $ tail -f ~/access.log | ack --passthru 123.45.67.89

--print0

Only works in conjunction with -f, -g, -l or -c (filename output). The filenamesare output separated with a null byte instead of the usual newline. This ishelpful 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 -gand -G options.

-r, -R, --recurse

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

--smart-case, --no-smart-case

Ignore case in the search strings if PATTERN contains no uppercasecharacters. This is similar to "smartcase" in vim. This option isoff by default.

-i always overrides this option.

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

--sort-files

Sorts the found files lexically. Use this if you want your filelistings to be deterministic between runs of ack.

--show-types

Outputs the filetypes that ack associates with each file.

Works with -f and -g options.

--thpppt

Display the all-important Bill The Cat logo. Note that the exactspelling of --thpppppt is not important. It's checked againsta 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 canalso be specified as --perl, and --type=noperl can be doneas --noperl.

If a file is of both type ``foo'' and ``bar'', specifying --foo and--nobar will exclude the file, because an exclusion takes precedenceover 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 (theexisting) type TYPE. See also ``Defining your own types''.

--type-set TYPE=.EXTENSION[,.EXT2[,...]]

Files with the given EXTENSION(s) are recognized as being of typeTYPE. 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 -gand -G options.

--version

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 -gand -G options.

-1

Stops after reporting first match of any kind. This is differentfrom --max-count=1 or -m1, where only one match per file isshown. Also, -1 works with -f and -g, where -m doesnot.

THE .ackrc FILE

The .ackrc file contains command-line options that are prependedto the command line before processing. Multiple options may liveon multiple lines. Lines beginning with a # are ignored. A .ackrcmight look like this:

    # Always sort the files    --sort-files    # Always color, even if piping to a another program    --color    # 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 linein the .ackrc file is interpreted as one element of @ARGV.

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

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

Defining your own types

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

ack --perl foo searches for foo in all perl files. ack --help=typestells you, that perl files are files endingin .pl, .pm, .pod or .t. So what if you would like to include .xsfiles as well when searching for --perl files? ack --type-add perl=.xs --perl foodoes this for you. --type-add appendsadditional extensions to an existing type.

If you want to define a new type, or completely redefine an existingtype, then use --type-set. ack --type-seteiffel=.e,.eiffel defines the type eiffel to include files withthe extensions .e or .eiffel. So to search for all eiffel filescontaining the word Bertrand use ack --type-set eiffel=.e,.eiffel --eiffel Bertrand.As usual, you can also write --type=eiffelinstead of --eiffel. Negation also works, so --noeiffel excludesall eiffel files from a search. Redefining also works: ack --type-set cc=.c,.hand .xs files no longer belong to the type cc.

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

  --type-set=eiffel=.e,.eiffel

or writing on separate lines

  --type-set  eiffel=.e,.eiffel

The following does NOT work in the .ackrc file:

  --type-set eiffel=.e,.eiffel

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

Restrictions:

•: The types 'skipped', 'make', 'binary' and 'text' are considered ``builtin'' andcannot be altered.
•: The shebang line recognition of the types 'perl', 'ruby', 'php', 'python','shell' and 'xml' cannot be redefined by --type-set, it is alwaysactive. However, the shebang line is only examined for files where theextension is not recognised. Therefore it is possible to sayack --type-set perl=.perl --type-set foo=.pl,.pm,.pod,.t --perl --nofoo andonly find your shiny new .perl files (and all files with unrecognized extensionand perl on the shebang line).

ENVIRONMENT VARIABLES

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

ACKRC

Specifies the location of the .ackrc file. If this file doesn'texist, ack looks in the default location.

ACK_OPTIONS

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

ACK_COLOR_FILENAME

Specifies the color of the filename when it's printed in --groupmode. 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 thebackground color.

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

ACK_COLOR_MATCH

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

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

See ACK_COLOR_FILENAME for the color specifications.

ACK_COLOR_LINENO

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

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

See ACK_COLOR_FILENAME for the color specifications.

ACK_PAGER

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

Using "ACK_PAGER" does not suppress grouping and coloring likepiping output on the command-line does, except that on Windowsack will assume that "ACK_PAGER" does not support color.

"ACK_PAGER_COLOR" overrides "ACK_PAGER" if both are specified.

ACK_PAGER_COLOR

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

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

ACK & OTHER TOOLS

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 mayuse other default flags. Now you can search with ack and easilystep through the results in Vim:

  :grep Dumper perllib

Emacs integration

Phil Jackson put together an ack.el extension that ``provides asimple compilation mode ... has the ability to guess what files youwant to search for based on the major-mode.''

<http://www.shellarchive.co.uk/content/emacs.html>

TextMate integration

Pedro Melo is a TextMate user who writes "I spend my day mostlyinside TextMate, and the built-in find-in-project sucks with largeprojects. So I hacked a TextMate command that was using find +grep to use ack. The result is the Search in Project with ack, andyou can find it here:<http://www.simplicidade.org/notes/archives/2008/03/search_in_proje.html>"

Shell and Return Code

For greater compatibility with grep, ack in normal use returnsshell return or exit code of 0 only if something is found and 1 ifno 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 onefile is found. If no files are found, then 1 is returned.

DEBUGGING ACK PROBLEMS

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'renot expecting, or forgotten you specified. Use --noenv to ignoreyour environment and .ackrc.

Use -f to see what files you're scanning

The reason I created -f in the first place was as a debuggingtool. If ack is not finding matches you think it should find, runack -f to see what files are being checked.

TIPS

Use the .ackrc file.

The .ackrc is the place to put all your options you use most ofthe time but don't want to remember. Put all your --type-add and--type-set definitions in it. If you like --smart-case, set itthere, 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 alist 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/thatg/' $(ack -f --perl)

Use -Q when in doubt about metacharacters

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

Use ack to watch log files

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

    ack -Q aa.bb.cc.dd /path/to/access.log | ack -Q -B5 troublesome.gif

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

Share your knowledge

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

FAQ

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

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

Use the "-f" switch to see a list of files that ack will searchfor you.

If you want ack to search files that it doesn't recognize, use the"-a" switch.

If you want ack to search every file, even ones that it alwaysignores like coredumps and backup files, use the "-u" switch.

Why does ack ignore unknown files by default?

ack is designed by a programmer, for programmers, for searchinglarge trees of code. Most codebases have a lot files in them whicharen't source files (like compiled object files, source controlmetadata, etc), and grep wastes a lot of time searching through allof those as well and returning matches from those files.

That's why ack's behavior of not searching things it doesn't recognizeis one of its greatest strengths: the speed you get from onlysearching the things that you want to be looking at.

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

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

You can certainly use ack to select your files to update. Forexample, to change all ``foo'' to ``bar'' in all PHP files, you can dothis from the Unix shell:

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

Can you make ack recognize .xyz files?

That's an enhancement. Please see the section in the manual aboutenhancements.

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 packageout there called ``ack'' that has nothing to do with this ack.

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

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

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

What does ack mean?

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

Can I do multi-line regexes?

No, ack does not support regexes that match multiple lines. Doingso 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.

AUTHOR

Andy Lester, "<andy at petdance.com>"

BUGS

Please report any bugs or feature requests to the issues list atGithub: <http://github.com/petdance/ack/issues>

ENHANCEMENTS

All enhancement requests MUST first be posted to the ack-usersmailing list at http://groups.google.com/group/ack-users <http://groups.google.com/group/ack-users>. Iwill not consider a request without it first getting seen by otherack users. This includes requests for new filetypes.

There is a list of enhancements I want to make to ack in the ackissues list at Github: <http://github.com/petdance/ack/issues>

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

SUPPORT

Support for and information about ack can be found at:

•: The ack homepage
<http://betterthangrep.com/>
•: The ack issues list at Github
<http://github.com/petdance/ack/issues>
•: AnnoCPAN: Annotated CPAN documentation
<http://annocpan.org/dist/ack>
•: CPAN Ratings
<http://cpanratings.perl.org/d/ack>
•: Search CPAN
<http://search.cpan.org/dist/ack>
•: Git source repository
<http://github.com/petdance/ack>

ACKNOWLEDGEMENTS

How appropriate to have acknowledgements!

Thanks to everyone who has contributed to ack in any way, includingMatthew 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,Gabor Szabo,Tod Hagan,Michael Hendricks,var Arnfjo.rd- 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 Bjorn Hansen,Jerry Gay,Will Coleda,Mike O'Regan,Slaven ReziX,Mark Stosberg,David Alan Pisoni,Adriano Ferreira,James Keenan,Leland Johnson,Ricardo Signesand Pete Krawczyk.