Glob (programming)

The glob command, short for global, originates in the earliest versions of Bell Labs' Unix. 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: • 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. Both ReactOS (crt/misc/getargs.c) and Wine (msvcrt/data.c) 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. 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. SQL The SQL operator has an equivalent to and but not . 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. 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. 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. == Other implementations==

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: • C and C++ do not have built-in support for glob patterns in the ISO-defined standard libraries, however on Unix-like systems C and C++ may include from the C POSIX library to use ::glob(). • C++ itself does not have direct support for glob patterns, however they may be approximated using the and headers, using std::filesystem::directory_iterator and std::regex_match(). • C++ has external libraries, such as POCO C++ Libraries, which includes a Glob class which can act on glob patterns. • C# provides the official extension library Microsoft.Extensions.FileSystemGlobbing, which contains class Matcher. • C# also has multiple external libraries available through NuGet such as Glob the most popular of these being the glob crate which itself has a glob() function. • SQLite has a GLOB function. • Tcl contains a globbing facility. ==See also==