Glob (programming)

File:Unix Glob Reference.png

A screenshot of the original 1971 Unix reference page for glob – the owner is dmr, short for Dennis MacAlistair Ritchie.

Template:Mono (Template:IPAc-en) 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 (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.<ref name="man7Unix1"/> 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: Template:Mono. 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.<ref name="reader">Template:Cite tech report</ref> 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.<ref name=fnmatch3>Template:Man</ref><ref>Template:Man</ref> 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 Template:Code, Template:Code, and Template:Code.

Wildcard	Description	Example	Matches	Does not match
Template:Code	matches any number of any characters including none	Template:Code	Template:Code, Template:Code, or Template:Code	Template:Code, Template:Code, or Template:Code
		Template:Code	Template:Code, Template:Code, or Template:Code.	Template:Code, or Template:Code
Template:Code	matches any single character	Template:Code	Template:Code, Template:Code, Template:Code or Template:Code	Template:Code
Template:Code	matches one character given in the bracket	Template:Code	Template:Code or Template:Code	Template:Code, Template:Code or Template:Code
Template:Code	matches one character from the (locale-dependent) range given in the bracket	Template:Code	Template:Code, Template:Code, Template:Code up to Template:Code	Template:Code, Template:Code or Template:Code

Normally, the path separator character (Template:Code on Linux/Unix, MacOS, etc. or Template:Code on Windows) will never be matched. Some shells, such as Unix shell have functionality allowing users to circumvent this.<ref>https://www.gnu.org/software/bash/manual/bash.html#Pattern-Matching Template:Webarchive Bash Reference Manual</ref>

Unix-likeTemplate:Anchor

On Unix-like systems Template:Code, Template:Code is defined as above while Template:Code has two additional meanings:<ref name="posixglob"/><ref name="linuxglob7"/>

Wildcard	Description	Example	Matches	Does not match
Template:Code	matches one character that is not given in the bracket	Template:Code	Template:Code, Template:Code, or Template:Code	Template:Code
Template:Code	matches one character that is not from the range given in the bracket	Template:Code	Template:Code, Template:Code, Template:Code up to Template:Code and Template:Code etc.	Template:Code, Template:Code, Template:Code or Template:Code

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.<ref name="posixglob"/><ref name="linuxglob7"/>

Unix globbing is handled by the shell per POSIX tradition. Globbing is provided on filenames at the command line and in shell scripts.<ref name="ABSGlob"/> 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:<ref>Template:Cite web</ref>

• 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 Template:Code shell option. This option came from ksh93.<ref name="bashpat"/> The GNU fnmatch and glob has an identical extension.<ref name=fnmatch3/>
• globstar: allows ** on its own as a name component to recursively match any number of layers of non-hidden directories.<ref name="bashpat"/> Also supported by the JavaScript libraries and Python's glob.

Windows and DOS

[[File:IBM PC DOS 1.0 screenshot.png|thumb|The [[dir (command)|Template:Code]] command with a glob pattern in IBM PC DOS 1.0.]]

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.<ref name="pwshcmdlet"/>
• COMMAND.COM and cmd.exe have most of the common syntax with some limitations: There is no Template:Code and for COMMAND.COM the Template:Code 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.

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:<ref name="winWildcard"/>

• The Microsoft C Runtime (msvcrt) command-line expander, which only supports Template:Code and Template:Code.<ref>Template:Cite web</ref> Both ReactOS (crt/misc/getargs.c) and Wine (msvcrt/data.c) contain a compatible open-source implementation of Template:Code, the function operating under-the-hood, in their core CRT.
• The Cygwin and MSYS Template:Code command-line expander, which uses the unix-style Template:Code 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, Template:Code. On the Windows API end, the Template:Tt equivalent is Template:Tt, and Template:Tt corresponds to its underlying Template:Tt.<ref>Wildcards in Windows Template:Webarchive. MSDN Devblog.</ref> (Another fnmatch analogue is Template:Tt.) Both open-source msvcrt expanders use Template:Tt, so 8.3 filename quirks will also apply in them.

SQL

The SQL Template:Code operator has an equivalent to Template:Code and Template:Code but not Template:Code.

Common wildcard	SQL wildcard	Description
Template:Code	Template:Code	matches any single character
Template:Code	Template:Code	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 (Template:Code) matches zero or more characters and the underscore (Template:Code) matches exactly one.

Many implementations of SQL have extended the LIKE operator to allow a richer pattern-matching language, incorporating character ranges (Template:Code), their negation, and elements of regular expressions.<ref name="transact-sql-like"/>

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.<ref>Template:Cite book</ref>

Common wildcard	Equivalent regular expression
Template:Code	Template:Code
Template:Code	Template:Code

Globs attempt to match the entire string (for example, Template:Code 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.<ref name=py>Template:Cite web</ref>

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 <glob.h> 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 <filesystem> and <regex> 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.<ref>Template:Cite web</ref>
• C# provides the official extension library Microsoft.Extensions.FileSystemGlobbing,<ref>Template:Cite web</ref> which contains class Matcher.<ref>Template:Cite web</ref>
  • C# also has multiple external libraries available through NuGet such as Glob<ref name="dotnet-glob"/> or DotNet.Glob.<ref name="dotnet.glob"/>
• D has a globMatch function in the std.path module.<ref name="dlang"/>
• Go has a Glob function in the filepath package.<ref name="golang"/>
• Java provides package java.nio.file which contains class Files,<ref name="java"/> which has methods such as <syntaxhighlight lang="java" inline>Files.newDirectoryStream(Path dir, String glob)</syntaxhighlight> for operating over glob patterns and returns DirectoryStream<Path>. The package also contains the classes FileSystems and PathMatcher for matching glob patterns.
• Haskell has a Glob package with the main module System.FilePath.Glob. The pattern syntax is based on a subset of Zsh's. It tries to optimize the given pattern and should be noticeably faster than a naïve character-by-character matcher.<ref name="hs"/>
• Node.js has a glob function in the node:fs module.<ref name="nodejs"/>
• Perl has both a glob function (as discussed in Larry Wall's book Programming Perl) and a Glob extension which mimics the BSD glob routine.<ref name="pl"/> Perl's angle brackets can be used to glob as well: <*.log>.
• PHP has a glob function.<ref name="php"/>
• Python has a glob module in the standard library which performs wildcard pattern matching on filenames,<ref name="pyglob"/> and an fnmatch module with functions for matching strings or filtering lists based on these same wildcard patterns.<ref name=py/> Guido van Rossum, author of the Python programming language, wrote and contributed a glob routine to BSD Unix in 1986.<ref name="isc-glob"/> There were previous implementations of glob, e.g., in the ex and ftp programs in previous releases of BSD.
• Ruby has a glob method for the Dir class which performs wildcard pattern matching on filenames.<ref name="rbdir"/> Several libraries such as Rant and Rake provide a FileList class which has a glob method or use the method FileList.[] identically.
• Rust has multiple libraries that can match glob patterns,<ref>Template:Cite web</ref> the most popular of these being the glob crate which itself has a glob() function.<ref>Template:Cite web</ref>
• SQLite has a GLOB function.
• Tcl contains a globbing facility.<ref name="tcl"/>

See also

• Regular expression
• Wildcard character
• Matching wildcards