Regular expression to extract text between square brackets

Question

Simple regex question. I have a string on the following format:

this is a [sample] string with [some] special words. [another one]

What is the regular expression to extract the words within the square brackets, ie.

sample
some
another one

Note: In my use case, brackets cannot be nested.

score 896 · Accepted Answer · answered Mar 08 '10 at 17:15

896

You can use the following regex globally:

\[(.*?)\]

Explanation:

\[ : [ is a meta char and needs to be escaped if you want to match it literally.
(.*?) : match everything in a non-greedy way and capture it.
\] : ] is a meta char and needs to be escaped if you want to match it literally.

answered Mar 08 '10 at 17:15

codaddict

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The other answer's method, using `[^]]` is faster than non-greedy (`?`), and also works with regex flavours that don't support non-greedy. However, non-greedy looks nicer. – Ipsquiggle Mar 08 '10 at 17:24
218

How to exclude `[` `]` from output(result)? – Mickey Tin Apr 28 '13 at 22:46
12

@MickeyTin, if you are using Java, you can group it using group(1) over just group(), so the '[]' will not go together – andolffer.joseph Sep 19 '13 at 16:47
Can you please provide 'sed' and 'awk' examples to use this regex and extract text. Thanks. – valentt Jul 17 '15 at 14:37
25

This matches only the first occurrence – hfatahi Aug 06 '15 at 14:43
This works, but will not include additional closing brackets as part of the first capture group. To do this, use `\[(.*?]*)\]`. This will match `[[[sample]]]` such that `[[[sample]]]` is the matched string and `[[sample]]` is the first capture group. `[sample]]]` will also match `[sample]]]` with group one being `sample]]`, and `[[[sample]` will match `[[[sample]` with group one being `[[sample` – driima Oct 17 '15 at 14:44
Example to match all in php. $pattern = '#\[(.*?)\]#'; $string = 'This is a [brack] and [snares]'; preg_match_all($pattern, $string, $matches); – user1502826 Nov 26 '15 at 16:52
What if nested bracket contents like this.. [sample of [abc] in cd] – sarath Apr 05 '16 at 11:40
Note: to match all the occurrences use the method 'scan' http://stackoverflow.com/questions/80357/match-all-occurrences-of-a-regex – Alessandro De Simone Jun 11 '16 at 21:48
What will be the regex for var string = "@input [ Square_bracket ]". Please Suggest – Oct 17 '17 at 05:48
12

How do you exclude the brackets from the return? – jzadra Apr 04 '18 at 22:44
1

@MickeyTin in JS you can use `var stringWithoutBrackets = stringWithBrackets.replace(/[\[\]']+/g,'')` See [this answer from Mark](https://stackoverflow.com/a/3812077/9360197) – user2018 Oct 24 '18 at 11:22
https://stackoverflow.com/a/2403148/2260920 explains a solution where if there is whitespace like enter inside the brackets. – XPD May 20 '20 at 07:44
If I want only text in the blanket and erase the outsides, how can I do? – Bonn Jun 24 '20 at 08:22
@codaddict Man this is perfect, it saved me so much time! Thank you so much. – Ivan Yurchenko Oct 08 '20 at 12:51

score 152 · Answer 2 · edited Oct 13 '18 at 20:46

152

(?<=\[).+?(?=\])

Will capture content without brackets

(?<=\[) - positive lookbehind for [
.*? - non greedy match for the content
(?=\]) - positive lookahead for ]

EDIT: for nested brackets the below regex should work:

(\[(?:\[??[^\[]*?\]))

edited Oct 13 '18 at 20:46

морфиновые облака

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answered Dec 01 '14 at 09:20

Adam Moszczyński

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@igaurav I've checked it and it works. It will not work however in environments which does not support lookbehinds like Javascript. Maybe that is yours case? – Adam Moszczyński Feb 11 '15 at 06:21
Adam, your nested brackets solution fails when there is a string with a `.` in it... – patrick Dec 07 '15 at 02:54
2

People who write those regexps you are god damn magicians. Thank you so much! – Ivan Yurchenko Oct 08 '20 at 12:57
1

This should be the accepted answer since the asker specified the output without the brackets. The currently accepted answer will return `[ '[sample]', '[some]', '[another one]' ]` while this answer returns `[ 'sample', 'some', 'another one' ]`. – iandllnghm Nov 13 '20 at 21:58
The "positive lookbehind" feature may not be supported in all browsers. – Tigerrrrr Nov 15 '20 at 14:55

jasonbar · Answer 3 · 2010-03-08T17:30:34.720

94

This should work out ok:

\[([^]]+)\]

edited Mar 08 '10 at 17:30

answered Mar 08 '10 at 17:14

jasonbar

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In my use case, the bracketed text may include new lines, and this regex works, while the accepted answer does not. – Dave Jun 08 '13 at 04:59
1

what does the character class [^]] mean? What does it match? – Richard Sep 15 '13 at 13:25
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@Richard, The ^ negates the character class. It means "any character that is not a ]". – jasonbar Sep 16 '13 at 12:46
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I think it doesn't work as expected, you should use `\[([^\[\]]*)\]` to get the content in the most inner bracket. If you look into `lfjlksd [ded[ee]22]` then `\[([^]]+)\]` will get you `[ded[ee]` while the proposed expression would return `[ee]`. testede in [link](http://regexpal.com/) – TMC Apr 02 '14 at 14:45
2

Can you please provide 'sed' and 'awk' examples to use this regex and extract text. Thanks. – valentt Jul 17 '15 at 14:37
This is the most robust way for complex situations. – Hong Nov 25 '18 at 06:22
This works if the content inside the brackets has whitespace. – XPD May 20 '20 at 07:44

score 35 · Answer 4 · answered Mar 08 '10 at 17:15

35

Can brackets be nested?

If not: \[([^]]+)\] matches one item, including square brackets. Backreference \1 will contain the item to be match. If your regex flavor supports lookaround, use

(?<=\[)[^]]+(?=\])

This will only match the item inside brackets.

answered Mar 08 '10 at 17:15

Tim Pietzcker

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@KunalMukherjee: No, the regex can match any number of times. But some regex flavors needs to be told explicitly to apply the regex repeatedly (for example, by using the `/g` flag in JavaScript). – Tim Pietzcker Dec 08 '17 at 15:30

LJ Germain · Answer 5 · 2019-05-22T20:04:08.107

If you do not want to include the brackets in the match, here's the regex: (?<=\[).*?(?=\])

Let's break it down

The . matches any character except for line terminators. The ?= is a positive lookahead. A positive lookahead finds a string when a certain string comes after it. The ?<= is a positive lookbehind. A positive lookbehind finds a string when a certain string precedes it. To quote this,

Look ahead positive (?=)

Find expression A where expression B follows:

A(?=B)

Look behind positive (?<=)

Find expression A where expression B precedes:

(?<=B)A

The Alternative

If your regex engine does not support lookaheads and lookbehinds, then you can use the regex \[(.*?)\] to capture the innards of the brackets in a group and then you can manipulate the group as necessary.

How does this regex work?

The parentheses capture the characters in a group. The .*? gets all of the characters between the brackets (except for line terminators, unless you have the s flag enabled) in a way that is not greedy.

score 12 · Answer 6 · edited Nov 10 '19 at 17:14

12

(?<=\[).*?(?=\]) works good as per explanation given above. Here's a Python example:

import re 
str = "Pagination.go('formPagination_bottom',2,'Page',true,'1',null,'2013')"
re.search('(?<=\[).*?(?=\])', str).group()
"'formPagination_bottom',2,'Page',true,'1',null,'2013'"

edited Nov 10 '19 at 17:14

LJ Germain

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answered Apr 24 '15 at 00:03

devd

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You should always use code formatting for regexes, wherever they appear. If the regex is in the text rather than a code block, you can use backticks to format them. ([ref](http://stackoverflow.com/editing-help#comment-formatting)) – Alan Moore Apr 24 '15 at 01:28
1

Also, the question was about square brackets (`[]`), not parentheses. – Alan Moore Apr 24 '15 at 01:32

Emma · Answer 7 · 2019-11-10T18:03:24.887

Just in case, you might have had unbalanced brackets, you can likely design some expression with recursion similar to,

\[(([^\]\[]+)|(?R))*+\]

which of course, it would relate to the language or RegEx engine that you might be using.

RegEx Demo 1

Other than that,

\[([^\]\[\r\n]*)\]

RegEx Demo 2

or,

(?<=\[)[^\]\[\r\n]*(?=\])

RegEx Demo 3

are good options to explore.

If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.

RegEx Circuit

jex.im visualizes regular expressions:

Test

const regex = /\[([^\]\[\r\n]*)\]/gm;
const str = `This is a [sample] string with [some] special words. [another one]
This is a [sample string with [some special words. [another one
This is a [sample[sample]] string with [[some][some]] special words. [[another one]]`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }
    
    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

Source

Regular expression to match balanced parentheses

score 6 · Answer 8 · answered Jun 01 '20 at 09:17

To match a substring between the first [ and last ], you may use

\[.*\]            # Including open/close brackets
\[(.*)\]          # Excluding open/close brackets (using a capturing group)
(?<=\[).*(?=\])   # Excluding open/close brackets (using lookarounds)

See a regex demo and a regex demo #2.

Use the following expressions to match strings between the closest square brackets:

Including the brackets:
- \[[^][]*] - PCRE, Python re/regex, .NET, Golang, POSIX (grep, sed, bash)
- \[[^\][]*] - ECMAScript (JavaScript, C++ std::regex, VBA RegExp)
- \[[^\]\[]*] - Java regex
- \[[^\]\[]*\] - Onigmo (Ruby, requires escaping of brackets everywhere)
Excluding the brackets:
- (?<=\[)[^][]*(?=]) - PCRE, Python re/regex, .NET (C#, etc.), ICU (R stringr), JGSoft Software
- \[([^][]*)] - Bash, Golang - capture the contents between the square brackets with a pair of unescaped parentheses, also see below
- \[([^\][]*)] - JavaScript, C++ std::regex, VBA RegExp
- (?<=\[)[^\]\[]*(?=]) - Java regex
- (?<=\[)[^\]\[]*(?=\]) - Onigmo (Ruby, requires escaping of brackets everywhere)

NOTE: * matches 0 or more characters, use + to match 1 or more to avoid empty string matches in the resulting list/array.

Whenever both lookaround support is available, the above solutions rely on them to exclude the leading/trailing open/close bracket. Otherwise, rely on capturing groups (links to most common solutions in some languages have been provided).

If you need to match nested parentheses, you may see the solutions in the Regular expression to match balanced parentheses thread and replace the round brackets with the square ones to get the necessary functionality. You should use capturing groups to access the contents with open/close bracket excluded:

\[((?:[^][]++|(?R))*)] - PHP PCRE
\[((?>[^][]+|(?<o>)\[|(?<-o>]))*)] - .NET demo
\[(?:[^\]\[]++|(\g<0>))*\] - Onigmo (Ruby) demo

score 4 · Answer 9 · answered Sep 06 '19 at 09:57

if you want fillter only small alphabet letter between square bracket a-z

(\[[a-z]*\])

if you want small and caps letter a-zA-Z

(\[[a-zA-Z]*\])

if you want small caps and number letter a-zA-Z0-9

(\[[a-zA-Z0-9]*\])

if you want everything between square bracket

if you want text , number and symbols

(\[.*\])

Nezar Fadle · Answer 10 · 2015-01-06T09:28:43.733

3

This code will extract the content between square brackets and parentheses

(?:(?<=\().+?(?=\))|(?<=\[).+?(?=\]))

(?: non capturing group
(?<=\().+?(?=\)) positive lookbehind and lookahead to extract the text between parentheses
| or
(?<=\[).+?(?=\]) positive lookbehind and lookahead to extract the text between square brackets

edited Jan 06 '15 at 09:28

answered Jan 06 '15 at 09:22

Nezar Fadle

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score 3 · Answer 11 · answered Mar 15 '19 at 04:18

3

In R, try:

x <- 'foo[bar]baz'
str_replace(x, ".*?\\[(.*?)\\].*", "\\1")
[1] "bar"

answered Mar 15 '19 at 04:18

Tony Ladson

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..or `gsub(pat, "\\1", x, perl=TRUE)`, where `pat` is the regular expression you provided.. – Karsten W. Jul 16 '19 at 16:23

score 3 · Answer 12 · edited Dec 28 '12 at 13:25

3

([[][a-z \s]+[]])

Above should work given the following explaination

characters within square brackets[] defines characte class which means pattern should match atleast one charcater mentioned within square brackets
\s specifies a space
+ means atleast one of the character mentioned previously to +.

edited Dec 28 '12 at 13:25

Peon

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answered May 23 '11 at 12:44

spooks

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In sensitive cases `A-Z` should add to pattern : `([[][a-zA-Z \s]+[]])` ; I think it's good way, while `\ ` in regex patterns that defines in string marks ( " and ' ) and mixing up newbies by backslash handling in " or ' usages! – MohaMad Mar 01 '17 at 10:46
the only answer that worked for me for C++ regex (except im doing it with quotations instead of brackets). `std::regex pattern{R"(["][a-zA-Z \s]+["])"};` – StackAttack Oct 01 '18 at 05:42

score 3 · Answer 13 · answered Sep 02 '20 at 14:44

3

The @Tim Pietzcker's answer here

(?<=\[)[^]]+(?=\])

is almost the one I've been looking for. But there is one issue that some legacy browsers can fail on positive lookbehind. So I had to made my day by myself :). I manged to write this:

/([^[]+(?=]))/g

Maybe it will help someone.

console.log("this is a [sample] string with [some] special words. [another one]".match(/([^[]+(?=]))/g));

answered Sep 02 '20 at 14:44

Michał Grzegorzewski

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perfect answer I was looking for – Asanka Siriwardena Nov 30 '20 at 14:11

score 1 · Answer 14 · answered May 20 '20 at 18:19

1

I needed including newlines and including the brackets

\[[\s\S]+\]

answered May 20 '20 at 18:19

citynorman

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score 0 · Answer 15 · answered Dec 03 '20 at 13:26

0

If someone wants to match and select a string containing one or more dots inside square brackets like "[fu.bar]" use the following:

(?<=\[)(\w+\.\w+.*?)(?=\])

Regex Tester

answered Dec 03 '20 at 13:26

Andreas

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Regular expression to extract text between square brackets

15 Answers15

Let's break it down

Look ahead positive (?=)

`A(?=B)`

Look behind positive (?<=)

`(?<=B)A`