In computer programming, glob () patterns specify sets of filenames with wildcard characters. For example, the Unix Bash shell command mv *.txt textfiles/ moves (mv) all files with names ending in .txt from the current directory to the directory textfiles. Here, * is a wildcard standing for "any string of characters except /" and *.txt is a glob pattern. The other common wildcard is the question mark (?), which stands for one character. For example, mv ?.txt shorttextfiles/ will move all files named with a single character followed by .txt from the current directory to directory shorttextfiles, while ??.txt would match all files whose name consists of 2 characters followed by .txt.
In addition to matching filenames, globs are also used widely for matching arbitrary strings (wildcard matching). In this capacity a common interface is fnmatch.
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 Bash 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 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 JS 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:
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.