Glob (programming)
' 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
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 fall into two groups, and can be applied to any character sequence, not just to directory entries.
- "Metacharacters" :
- *
?matches any character exactly once. - *
*matches a string of zero or more characters. - "Ranges/sets":
- *
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, Z shell, Almquist shell 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 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,
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 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, 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.| Wildcard | Description | Example | Matches | Does not match |
| matches any number of any characters including none | ,, or | ,, or | ||
| matches any number of any characters including none | ,, or. | , or | ||
| matches any single character | ,, or | |||
| matches one character given in the bracket | or | , or | ||
| matches one character from the range given in the bracket | ,, up to | , or |
Normally, the path separator character 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:| Wildcard | Description | Example | Matches | Does not match |
| matches one character that is not given in the bracket | ,, or | |||
| matches one character that is not from the range given in the bracket | ,, up to and etc. | ,, or |
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 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 : 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 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
- Windows PowerShell has all the common syntax defined as stated above without any additions.
- COMMAND.COM and cmd.exe have most of the common syntax with some limitations: There is no and for COMMAND.COM the may only appear at the end of the pattern. It can not appear in the middle of a pattern, except immediately preceding the filename extension separator dot.
- The Microsoft C Runtime command-line expander, which only supports and. Both ReactOS and Wine contain a compatible open-source implementation of, the function operating under-the-hood, in their core CRT.
- The Cygwin and MSYS command-line expander, which uses the unix-style routine under-the-hood, after splitting the arguments.
SQL
The SQL operator has an equivalent to and but not.| Common wildcard | SQL wildcard | Description |
| matches any single character | ||
| matches any number of any characters including none |
Standard SQL uses a glob-like syntax for simple string matching in its
LIKE 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
LIKE operator to allow a richer pattern-matching language, incorporating character ranges, their negation, and elements of regular expressions.Compared to 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.| Common wildcard | Equivalent regular expression |
Globs attempt to match the entire string, whereas, depending on implementation details, regular expressions may match a substring.
Implementing as regular expressions
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.