() is a libc 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 <code>glob()</code>-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 <code>glob()</code> function and the underlying <code>gmatch()</code> 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, <code>glob()</code> and <code>gmatch()</code> 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 <code>glob</code> and <code>find</code>; 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 <code>glob()</code> and <code>gmatch()</code>. 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.
As reimplementations of Bell Labs' UNIX proliferated, so did reimplementations of its Bell Labs' libc and shell, and with them <code>glob()</code> and globbing. Today, <code>glob()</code> 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.
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, 1969âÂÂ1975) relied on a separate program to expand wildcard characters in unquoted arguments to a command: '. 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, <code>glob()</code>, used by programs such as the shell. It is usually defined based on a function named <code>fnmatch()</code>, 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 <code>.</code>. For example, <code>*</code> matches all visible files while <code>.*</code> matches all hidden files.
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.
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 <code>case</code> 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 <code>case</code>. It is only expanded on the command line before globbing.
The Bash shell also supports the following extensions:
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:
Windows and DOS programs receive a long command-line string instead of argv-style parameters, and it is their responsibility to perform any splitting, quoting, or glob expansion. There is technically no fixed way of describing wildcards in programs since they are free to do what they wish. Two common glob expanders include:
Most other parts of Windows, including the Indexing Service, use the MS-DOS style of wildcards found in CMD. A relic of the 8.3 filename age, this syntax pays special attention to dots in the pattern and the text (filename). Internally this is done using three extra wildcard characters, . On the Windows API end, the equivalent is , and corresponds to its underlying . (Another fnmatch analogue is .) Both open-source msvcrt expanders use , so 8.3 filename quirks will also apply in them.
The SQL operator has an equivalent to and but not .
Standard SQL uses a glob-like syntax for simple string matching in its <code>LIKE</code> operator, although the term "glob" is not generally used in the SQL community. The percent sign () matches zero or more characters and the underscore () matches exactly one.
Many implementations of SQL have extended the <code>LIKE</code> operator to allow a richer pattern-matching language, incorporating character ranges (), their negation, and elements of regular expressions.
Globs do not include syntax for the Kleene star which allows multiple repetitions of the preceding part of the expression; thus they are not considered regular expressions, which can describe the full set of regular languages over any given finite alphabet.
Globs attempt to match the entire string (for example, matches S.DOC and SA.DOC, but not POST.DOC or SURREY.DOCKS), whereas, depending on implementation details, regular expressions may match a substring.
The original Mozilla proxy auto-config implementation, which provides a glob-matching function on strings, uses a replace-as-RegExp implementation as above. The bracket syntax happens to be covered by regex in such an example.
Python's fnmatch uses a more elaborate procedure to transform the pattern into a regular expression.
Beyond their uses in shells, globs patterns also find use in a variety of programming languages, mainly to process human input. A glob-style interface for returning files or an fnmatch-style interface for matching strings are found in the following programming languages: