glob() () is a POSIX C function for globbing, which is the archetypal use of pattern matching against the names in a filesystem directory such that a name pattern is expanded into a list of names matching that pattern. Although globbing may now refer to glob()-style pattern matching of any string, not just expansion into a list of filesystem names, the original meaning of the term is still widespread. The glob() function and the underlying gmatch() function originated at Bell Labs in the early 1970s alongside the original AT&T UNIX itself and had a formative influence on the syntax of UNIX command line utilities and therefore also on the present-day reimplementations thereof. In their original form, glob() and gmatch() derived from code used in Bell Labs in-house utilities that developed alongside the original Unix in the early 1970s. Among those utilities were also two command line tools called glob and find; each could be used to pass a list of matching filenames to other command line tools, and they shared the backend code subsequently formalized as glob() and gmatch(). Shell-statement-level globbing by default became commonplace following the "builtin"-integration of globbing-functionality into the 7th edition of the Unix shell in 1978. The Unix shell's -f option to disable globbing — i.e. revert to literal "file" mode — appeared in the same version. The glob pattern quantifiers now standardized by POSIX.2 (IEEE Std 1003.2) fall into two groups, and can be applied to any character sequence ("string"), not just to directory entries.
"Metacharacters" (also called "Wildcards"): ? (not in brackets) matches any character exactly once. * (not in brackets) matches a string of zero or more characters. "Ranges/sets": [...], where the first character within the brackets is not '!', matches any single character among the characters specified in the brackets. If the first character within brackets is '!', then the [!...] matches any single character that is not among the characters specified in the brackets. The characters in the brackets may be a list ([abc]) or a range ([a-c]) or denote a character class (like [[:space:]] where the inner brackets are part of the classname). POSIX does not mandate multi-range ([a-c0-3]) support, which derive originally from regular expressions. As reimplementations of Bell Labs' UNIX proliferated, so did reimplementations of its Bell Labs' libc and shell, and with them glob() and globbing. Today, glob() and globbing are standardized by the POSIX.2 specification and are integral part of every Unix-like libc ecosystem and shell, including AT&T Bourne shell-compatible Korn shell (ksh), Z shell (zsh), Almquist shell (ash) and its derivatives and reimplementations such as busybox, toybox, GNU bash, Debian dash.
Origin The glob command, short for global, originates in the earliest versions of Bell Labs' Unix. The command interpreters of the early versions of Unix (1st through 6th Editions, 1969–1975) relied on a separate program to expand wildcard characters in unquoted arguments to a command: /etc/glob. That program performed the expansion and supplied the expanded list of file paths to the command for execution. Glob was originally written in the B programming language. It was the first piece of mainline Unix software to be developed in a high-level programming language. Later, this functionality was provided as a C library function, glob(), used by programs such as the shell. It is usually defined based on a function named fnmatch(), which tests for whether a string matches a given pattern - the program using this function can then iterate through a series of strings (usually filenames) to determine which ones match. Both functions are a part of POSIX: the functions defined in POSIX.1 since 2001, and the syntax defined in POSIX.2. The idea of defining a separate match function started with wildmat (wildcard match), a simple library to match strings against Bourne Shell globs. Traditionally, globs do not match hidden files in the form of Unix dotfiles; to match them the pattern must explicitly start with .. For example, * matches all visible files while .* matches all hidden files.
Syntax The most common wildcards are *, ?, and […].
Normally, the path separator character (/ on Linux/Unix, MacOS, etc. or \ on Windows) will never be matched. Some shells, such as Unix shell have functionality allowing users to circumvent this.
Unix-like On Unix-like systems *, ? is defined as above while […] has two additional meanings:
The ranges are also allowed to include pre-defined character classes, equivalence classes for accented characters, and collation symbols for hard-to-type characters. They are defined to match up with the brackets in POSIX regular expressions. Unix globbing is handled by the shell per POSIX tradition. Globbing is provided on filenames at the command line and in shell scripts. The POSIX-mandated case statement in shells provides pattern-matching using glob patterns. Some shells (such as the C shell and Bash) support additional syntax known as alternation or brace expansion. Because it is not part of the glob syntax, it is not provided in case. It is only expanded on the command line before globbing. The Bash shell also supports the following extensions:
Extended globbing (extglob): allows other pattern matching operators to be used to match multiple occurrences of a pattern enclosed in parentheses, essentially providing the missing kleene star and alternation for describing regular languages. It can be enabled by setting the extglob shell option. This option came from ksh93. The GNU fnmatch and glob has an identical extension. globstar: allows ** on its own as a name component to recursively match any number of layers of non-hidden directories. Also supported by the JavaScript libraries and Python's glob.
Windows and DOS
The original DOS was a clone of CP/M designed to work on Intel's 8088 and 8086 processors. Windows shells, following DOS, do not traditionally perform any glob expansion in arguments passed to external programs. Shells may use an expansion for their own builtin commands:
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