Bash-like brace expansion, implemented in JavaScript. Safer than other brace expansion libs, with complete support for the Bash 4.3 braces specification, without sacrificing speed.

Please consider following this project's author, Jon Schlinkert, and consider starring the project to show your ❤️ and support.

Install with npm:

$ npm install --save braces

See the changelog for details.

Brace patterns make globs more powerful by adding the ability to match specific ranges and sequences of characters.

• Accurate - complete support for the Bash 4.3 Brace Expansion specification (passes all of the Bash braces tests)
• fast and performant - Starts fast, runs fast and scales well as patterns increase in complexity.
• Organized code base - The parser and compiler are easy to maintain and update when edge cases crop up.
• Well-tested - Thousands of test assertions, and passes all of the Bash, minimatch, and brace-expansion unit tests (as of the date this was written).
• Safer - You shouldn't have to worry about users defining aggressive or malicious brace patterns that can break your application. Braces takes measures to prevent malicious regex that can be used for DDoS attacks (see catastrophic backtracking).
• Supports lists - (aka "sets") a/{b,c}/d => ['a/b/d', 'a/c/d']
• Supports sequences - (aka "ranges") {01..03} => ['01', '02', '03']
• Supports steps - (aka "increments") {2..10..2} => ['2', '4', '6', '8', '10']
• Supports escaping - To prevent evaluation of special characters.

The main export is a function that takes one or more brace patterns and options.

const braces = require('braces');
// braces(patterns[, options]);

console.log(braces(['{01..05}', '{a..e}']));
//=> ['(0[1-5])', '([a-e])']

console.log(braces(['{01..05}', '{a..e}'], { expand: true }));
//=> ['01', '02', '03', '04', '05', 'a', 'b', 'c', 'd', 'e']

By default, brace patterns are compiled into strings that are optimized for creating regular expressions and matching.

Compiled

console.log(braces('a/{x,y,z}/b'));
//=> ['a/(x|y|z)/b']
console.log(braces(['a/{01..20}/b', 'a/{1..5}/b']));
//=> [ 'a/(0[1-9]|1[0-9]|20)/b', 'a/([1-5])/b' ]

Expanded

Enable brace expansion by setting the expand option to true, or by using braces.expand() (returns an array similar to what you'd expect from Bash, or echo {1..5}, or minimatch):

console.log(braces('a/{x,y,z}/b', { expand: true }));
//=> ['a/x/b', 'a/y/b', 'a/z/b']

console.log(braces.expand('{01..10}'));
//=> ['01','02','03','04','05','06','07','08','09','10']

Expand lists (like Bash "sets"):

console.log(braces('a/{foo,bar,baz}/*.js'));
//=> ['a/(foo|bar|baz)/*.js']

console.log(braces.expand('a/{foo,bar,baz}/*.js'));
//=> ['a/foo/*.js', 'a/bar/*.js', 'a/baz/*.js']

Expand ranges of characters (like Bash "sequences"):

console.log(braces.expand('{1..3}')); // ['1', '2', '3']
console.log(braces.expand('a/{1..3}/b')); // ['a/1/b', 'a/2/b', 'a/3/b']
console.log(braces('{a..c}', { expand: true })); // ['a', 'b', 'c']
console.log(braces('foo/{a..c}', { expand: true })); // ['foo/a', 'foo/b', 'foo/c']

// supports zero-padded ranges
console.log(braces('a/{01..03}/b')); //=> ['a/(0[1-3])/b']
console.log(braces('a/{001..300}/b')); //=> ['a/(0{2}[1-9]|0[1-9][0-9]|[12][0-9]{2}|300)/b']

See fill-range for all available range-expansion options.

Steps, or increments, may be used with ranges:

console.log(braces.expand('{2..10..2}'));
//=> ['2', '4', '6', '8', '10']

console.log(braces('{2..10..2}'));
//=> ['(2|4|6|8|10)']

When the .optimize method is used, or options.optimize is set to true, sequences are passed to to-regex-range for expansion.

Brace patterns may be nested. The results of each expanded string are not sorted, and left to right order is preserved.

"Expanded" braces

console.log(braces.expand('a{b,c,/{x,y}}/e'));
//=> ['ab/e', 'ac/e', 'a/x/e', 'a/y/e']

console.log(braces.expand('a/{x,{1..5},y}/c'));
//=> ['a/x/c', 'a/1/c', 'a/2/c', 'a/3/c', 'a/4/c', 'a/5/c', 'a/y/c']

"Optimized" braces

console.log(braces('a{b,c,/{x,y}}/e'));
//=> ['a(b|c|/(x|y))/e']

console.log(braces('a/{x,{1..5},y}/c'));
//=> ['a/(x|([1-5])|y)/c']

Escaping braces

A brace pattern will not be expanded or evaluted if either the opening or closing brace is escaped:

console.log(braces.expand('a\\{d,c,b}e'));
//=> ['a{d,c,b}e']

console.log(braces.expand('a{d,c,b\\}e'));
//=> ['a{d,c,b}e']

Escaping commas

Commas inside braces may also be escaped:

console.log(braces.expand('a{b\\,c}d'));
//=> ['a{b,c}d']

console.log(braces.expand('a{d\\,c,b}e'));
//=> ['ad,ce', 'abe']

Single items

Following bash conventions, a brace pattern is also not expanded when it contains a single character:

console.log(braces.expand('a{b}c'));
//=> ['a{b}c']

Type: Number

Default: 10,000

Description: Limit the length of the input string. Useful when the input string is generated or your application allows users to pass a string, et cetera.

console.log(braces('a/{b,c}/d', { maxLength: 3 })); //=> throws an error

Type: Boolean

Default: undefined

Description: Generate an "expanded" brace pattern (alternatively you can use the braces.expand() method, which does the same thing).

console.log(braces('a/{b,c}/d', { expand: true }));
//=> [ 'a/b/d', 'a/c/d' ]

Type: Boolean

Default: undefined

Description: Remove duplicates from the returned array.

Type: Number

Default: 1000

Description: To prevent malicious patterns from being passed by users, an error is thrown when braces.expand() is used or options.expand is true and the generated range will exceed the rangeLimit.

You can customize options.rangeLimit or set it to Inifinity to disable this altogether.

Examples

// pattern exceeds the "rangeLimit", so it's optimized automatically
console.log(braces.expand('{1..1000}'));
//=> ['([1-9]|[1-9][0-9]{1,2}|1000)']

// pattern does not exceed "rangeLimit", so it's NOT optimized
console.log(braces.expand('{1..100}'));
//=> ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14', '15', '16', '17', '18', '19', '20', '21', '22', '23', '24', '25', '26', '27', '28', '29', '30', '31', '32', '33', '34', '35', '36', '37', '38', '39', '40', '41', '42', '43', '44', '45', '46', '47', '48', '49', '50', '51', '52', '53', '54', '55', '56', '57', '58', '59', '60', '61', '62', '63', '64', '65', '66', '67', '68', '69', '70', '71', '72', '73', '74', '75', '76', '77', '78', '79', '80', '81', '82', '83', '84', '85', '86', '87', '88', '89', '90', '91', '92', '93', '94', '95', '96', '97', '98', '99', '100']

Type: Function

Default: undefined

Description: Customize range expansion.

Example: Transforming non-numeric values

const alpha = braces.expand('x/{a..e}/y', {
  transform(value, index) {
    // When non-numeric values are passed, "value" is a character code.
    return 'foo/'   String.fromCharCode(value)   '-'   index;
  },
});
console.log(alpha);
//=> [ 'x/foo/a-0/y', 'x/foo/b-1/y', 'x/foo/c-2/y', 'x/foo/d-3/y', 'x/foo/e-4/y' ]

Example: Transforming numeric values

const numeric = braces.expand('{1..5}', {
  transform(value) {
    // when numeric values are passed, "value" is a number
    return 'foo/'   value * 2;
  },
});
console.log(numeric);
//=> [ 'foo/2', 'foo/4', 'foo/6', 'foo/8', 'foo/10' ]

Type: Boolean

Default: undefined

Description: In regular expressions, quanitifiers can be used to specify how many times a token can be repeated. For example, a{1,3} will match the letter a one to three times.

Unfortunately, regex quantifiers happen to share the same syntax as Bash lists

The quantifiers option tells braces to detect when regex quantifiers are defined in the given pattern, and not to try to expand them as lists.

Examples

const braces = require('braces');
console.log(braces('a/b{1,3}/{x,y,z}'));
//=> [ 'a/b(1|3)/(x|y|z)' ]
console.log(braces('a/b{1,3}/{x,y,z}', { quantifiers: true }));
//=> [ 'a/b{1,3}/(x|y|z)' ]
console.log(braces('a/b{1,3}/{x,y,z}', { quantifiers: true, expand: true }));
//=> [ 'a/b{1,3}/x', 'a/b{1,3}/y', 'a/b{1,3}/z' ]

Type: Boolean

Default: undefined

Description: Do not strip backslashes that were used for escaping from the result.

Brace expansion is a type of parameter expansion that was made popular by unix shells for generating lists of strings, as well as regex-like matching when used alongside wildcards (globs).

In addition to "expansion", braces are also used for matching. In other words:

• brace expansion is for generating new lists
• brace matching is for filtering existing lists

{a,b,c}       => a b c
{a,b,c}{1,2}  => a1 a2 b1 b2 c1 c2

{1..9}        => 1 2 3 4 5 6 7 8 9
{4..-4}       => 4 3 2 1 0 -1 -2 -3 -4
{1..20..3}    => 1 4 7 10 13 16 19
{a..j}        => a b c d e f g h i j
{j..a}        => j i h g f e d c b a
{a..z..3}     => a d g j m p s v y

{a,b,c}{1..3}   => a1 a2 a3 b1 b2 b3 c1 c2 c3
foo/{a,b,c}/bar => foo/a/bar foo/b/bar foo/c/bar

foo/1/bar
foo/2/bar
foo/3/bar

baz/1/qux
baz/2/qux
baz/3/qux

foo/1/bar
foo/2/bar
foo/3/bar
baz/1/qux
baz/2/qux
baz/3/qux

{1,2}{3,4}      => (2X2)    => 13 14 23 24
{1,2}{3,4}{5,6} => (2X2X2)  => 135 136 145 146 235 236 245 246

{1,2,3}{4,5,6}{7,8,9} => (3X3X3) => 147 148 149 157 158 159 167 168 169 247 248
                                    249 257 258 259 267 268 269 347 348 349 357
                                    358 359 367 368 369

{1..100}{1..100}         => (100X100)     => 10,000 elements (38.4 kB)
{1..100}{1..100}{1..100} => (100X100X100) => 1,000,000 elements (5.76 MB)

Braces is not only screaming fast, it's also more accurate the other brace expansion libraries.

Fortunately there is a solution to the "brace bomb" problem: don't expand brace patterns into an array when they're used for matching.

Instead, convert the pattern into an optimized regular expression. This is easier said than done, and braces is the only library that does this currently.

The proof is in the numbers

Minimatch gets exponentially slower as patterns increase in complexity, braces does not. The following results were generated using braces() and minimatch.braceExpand(), respectively.

When you need expansion, braces is still much faster.

(the following results were generated using braces.expand() and minimatch.braceExpand(), respectively)

If you'd like to run these comparisons yourself, see test/support/generate.js.

Install dev dependencies:

npm i -d && npm benchmark

Braces is more accurate, without sacrificing performance.

● expand - range (expanded)
     braces x 53,167 ops/sec ±0.12% (102 runs sampled)
  minimatch x 11,378 ops/sec ±0.10% (102 runs sampled)
● expand - range (optimized for regex)
     braces x 373,442 ops/sec ±0.04% (100 runs sampled)
  minimatch x 3,262 ops/sec ±0.18% (100 runs sampled)
● expand - nested ranges (expanded)
     braces x 33,921 ops/sec ±0.09% (99 runs sampled)
  minimatch x 10,855 ops/sec ±0.28% (100 runs sampled)
● expand - nested ranges (optimized for regex)
     braces x 287,479 ops/sec ±0.52% (98 runs sampled)
  minimatch x 3,219 ops/sec ±0.28% (101 runs sampled)
● expand - set (expanded)
     braces x 238,243 ops/sec ±0.19% (97 runs sampled)
  minimatch x 538,268 ops/sec ±0.31% (96 runs sampled)
● expand - set (optimized for regex)
     braces x 321,844 ops/sec ±0.10% (97 runs sampled)
  minimatch x 140,600 ops/sec ±0.15% (100 runs sampled)
● expand - nested sets (expanded)
     braces x 165,371 ops/sec ±0.42% (96 runs sampled)
  minimatch x 337,720 ops/sec ±0.28% (100 runs sampled)
● expand - nested sets (optimized for regex)
     braces x 242,948 ops/sec ±0.12% (99 runs sampled)
  minimatch x 87,403 ops/sec ±0.79% (96 runs sampled)

$ npm install && npm test

$ npm install -g verbose/verb#dev verb-generate-readme && verb

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Copyright © 2019, Jon Schlinkert. Released under the MIT License.

This file was generated by verb-generate-readme, v0.8.0, on April 08, 2019.