Syntax and Features

Glob expressions resemble Unix paths, but are distinct from paths and support patterns that can be matched against file paths and directory trees (i.e., search). Pattern syntax is similar to that found in Unix shells and tools like git, though there are some important differences.

Here's an example of a glob expression:

**/*.{go,rs}

This glob matches any path with a final component ending with .go or .rs, such as ./wax/src/lib.rs or glob.go.

Glob syntax is opinionated and is not configurable. For example, with the exception of tree wildcards, patterns never match across component boundaries (separators) and cannot be configured to do so.

Wildcards¶

Wildcards match some amount of arbitrary text in paths and are the most fundamental pattern provided by globs (and likely the most familiar).

The zero-or-more wildcards * and $ match zero or more of any character within a component (never path separators). Zero-or-more wildcards cannot be adjacent to other zero-or-more wildcards. The * wildcard is eager and will match the longest possible text while the $ wildcard is lazy and will match the shortest possible text. When followed by a literal, * stops at the last occurrence of that literal while $ stops at the first occurence.

The exactly-one wildcard ? matches any single character within a component (never path separators). Exactly-one wildcards do not group automatically, so a pattern of contiguous wildcards such as ??? form distinct captures for each ? wildcard. An alternative can be used to group exactly-one wildcards into a single capture, such as {???}.

The tree wildcard ** matches any characters across zero or more components. This is the only pattern that implicitly matches across arbitrary component boundaries; all other patterns do not implicitly match across component boundaries. When a tree wildcard participates in a match and does not terminate the pattern, its captured text includes the trailing separator. If a tree wildcard does not participate in a match, then its captured text is an empty string.

Tree wildcards must be delimited by forward slashes or terminations (the beginning and/or end of an expression). Tree wildcards and path separators are distinct and any adjacent forward slashes that form a tree wildcard are parsed together. Rooting forward slashes in tree wildcards are meaningful and the glob expressions **/*.txt and /**/*.txt differ in that the former is relative (has no root) and the latter has a root.

If a glob expression consists solely of a tree wildcard, then it matches any and all paths and the complete contents of any and all directory trees, including the root.

Character Classes¶

Character classes match any single character from a group of literals and ranges within a component (never path separators). Classes are delimited by square brackets [...]. Individual character literals are specified as is, such as [ab] to match either a or b. Character ranges are formed from two characters separated by a hyphen, such as [x-z] to match x, y, or z. Character classes match characters exactly and are always case-sensitive, so the expressions [ab] and {a,b} are not necessarily the same.

Any number of character literals and ranges can be used within a single character class. For example, [qa-cX-Z] matches any of q, a, b, c, X, Y, or Z.

Character classes may be negated by including an exclamation mark ! at the beginning of the class pattern. For example, [!a] matches any character except for a. These are the only patterns that support negation.

It is possible to escape meta-characters like *, $, etc., using character classes though globs also support escaping via a backslash \. To match the control characters [, ], and - within a character class, they must be escaped via a backslash, such as [a\-] to match a or -.

Character classes have notable platform-specific behavior, because they match arbitrary characters in native paths but never match path separators. This means that if a character class consists of only path separators on a given platform, then the character class is considered empty and matches nothing. For example, in the expression a[/]b the character class [/] matches nothing on Unix and Windows. Such character classes are not rejected, because the role of arbitrary characters depends on the platform. In practice, this is rarely a concern, but such patterns should be avoided.

Character classes have limited utility on their own, but compose well with repetitions.

Alternatives¶

Alternatives match an arbitrary sequence of one or more comma separated sub-globs delimited by curly braces {...,...}. For example, {a?c,x?z,foo} matches any of the sub-globs a?c, x?z, or foo. Alternatives may be arbitrarily nested and composed with repetitions.

Alternatives form a single capture group regardless of the contents of their sub-globs. This capture is formed from the complete match of the sub-glob, so if the alternative {a?c,x?z} matches abc, then the captured text will be abc (not b). Alternatives can be used to group captures using a single sub-glob, such as {*.{go,rs}} to capture an entire file name with a particular extension or {???} to group a sequence of exactly-one wildcards.

Alternatives must consider adjacency rules and neighboring patterns. For example, *{a,b*} is allowed but *{a,*b} is not. Additionally, they may not contain a sub-glob consisting of a singular tree wildcard ** and cannot root a glob expression as this could cause the expression to match or walk overlapping trees.

Repetitions¶

Repetitions match a sub-glob a specified number of times. Repetitions are delimited by angle brackets with a separating colon <...:...> where a sub-glob precedes the colon and an optional bounds specification follows it. For example, <a*/:0,> matches the sub-glob a*/ zero or more times. Though not implicit like tree wildcards, repetitions can match across component boundaries (and can themselves include tree wildcards). Repetitions may be arbitrarily nested and composed with alternatives.

Bound specifications are formed from inclusive lower and upper bounds separated by a comma ,, such as :1,4 to match between one and four times. The upper bound is optional and may be omitted. For example, :1, matches one or more times (note the trailing comma ,). A singular bound is convergent, so :3 matches exactly three times (both the lower and upper bounds are three). If no lower or upper bound is specified, then the sub-glob matches one or more times, so <a:> and <a:1,> are equivalent. Similarly, if the colon : is also omitted, then the sub-glob matches zero or more times, so <a> and <a:0,> are equivalent.

Repetitions form a singular capture group regardless of the contents of their sub-glob. The capture is formed from the complete match of the sub-glob. If the repetition <abc/> matches abc/abc/, then the captured text will be abc/abc/.

Repetitions compose well with character classes. Most often, a glob expression like {????} is sufficient, but the more specific expression <[0-9]:4> further constrains the matched characters to digits, for example. Repetitions may also be more terse, such as <?:8>. Furthermore, repetitions can form tree expressions that further constrain components, such as <[!.]*/>[!.]* to match paths that contain no leading dots . in any component.

Repetitions must consider adjacency rules and neighboring patterns. For example, a/<b/**:1,> is allowed but <a/**:1,>/b is not. Additionally, they may not contain a sub-glob consisting of a singular separator /, a singular zero-or-more wildcard * or $, nor a singular tree wildcard **. Repetitions with a lower bound of zero may not root a glob expression, as this could cause the expression to match or walk overlapping trees.

Flags and Case Sensitivity¶

Flags toggle the matching behavior of globs. Importantly, flags are a part of a glob expression rather than an API or behavior specific to an application. Behaviors are toggled immediately following flags in the order in which they appear in glob expressions. Flags are delimited by parenthesis with a leading question mark (?...) and may appear anywhere within a glob expression so long as they do not split tree wildcards (e.g., a/*(?i)* is not allowed). Each flag is represented by a single character and can be negated by preceding the corresponding character with a minus -. Flags are toggled in the order in which they appear within (?...).

The only supported flag is the case-insensitivty flag i. By default, glob expressions use the same case sensitivity as the target platforms's file system APIs (case-sensitive on Unix and case-insensitive on Windows), but i can be used to toggle this explicitly as needed. For example, (?-i)photos/**/*.(?i){jpg,jpeg} matches file paths beneath a photos directory with a case-sensitive base and a case-insensitive extension jpg or jpeg.