Glob - Globbing (Wildcard expression)

About

Glob is NOT a regular language but is wildly used to define a set of filenames with wildcard characters.

For instance, Bash provide globbing on filenames.

Wildcard / Syntax

The syntax is different by implementation and below are the most known pattern.

• The matchs of the wildcard characters is explained below
• All other characters match themselves.

Asterix

An asterisk (also known as star) , *, matches any number of characters (including none).

Example:

• *.html – Matches all strings that end in .html

Double Asterix

Two asterisks, **, works like * but crosses directory boundaries (ie complete paths) in a file system.

Example:

• The recursive globbing is always located before the last name in the path

src/**/*.c

Syntax and parsing rule: if the two asterisks, ** are followed by a /, this pattern will match only directories and subdirectories. See globstar in bash

**/

Question mark

A question mark, ?, matches exactly one character.

Example:

• ??? – Matches all strings with exactly three letters or digits
• a?*.java – Matches any string beginning with a, followed by at least one letter or digit, and ending with .java

Braces

Braces specify a collection of subpatterns. For example:

• {sun,moon,stars} matches “sun”, “moon”, or “stars”.
• {temp*,tmp*} matches all strings beginning with “temp” or “tmp”.
• *.{htm,html,pdf} – Matches any string ending with .htm, .html or .pdf
• {foo*,*[0-9]*} – Matches any string beginning with foo or any string containing a numeric value

Square brackets

Square brackets convey a set of single characters or, when the hyphen character (-) is used, a range of characters.

• [aeiou] matches any lowercase vowel.
• [0-9] matches any digit.
• [A-Z] matches any uppercase letter.
• [a-z,A-Z] matches any uppercase or lowercase letter.
• [!abc] exclusion does not match the set of characters abc
• Within the square brackets, *, ?, and \ match themselves.

Example:

• *[0-9]* – Matches all strings containing a numeric value

Escape

To match *, ?, or the other special characters, you can escape them by using the backslash character, \. For example:

• \\ matches a single backslash,
• \? matches the question mark.

Note: If you are typing the glob pattern at the console and it contains one of the special characters, you must:

• put the pattern in quotes (“*”),
• use the backslash (\*),
• or use whatever escape mechanism is supported at the command line.

Definition

A possible definition is that a string is a wildcard pattern when it contains one of the characters

• ? to matches any single character
• * to matches any string
• [ for character class definition
• { to define a list of pattern

Language

globbing in other languages

Bash

See filename expansion example

Node

• Node: https://github.com/isaacs/minimatch

Java

• newDirectoryStream(Path, Glob)
• getPathMatcher

Documentation / Reference

• wiki/Glob_(programming)
• http://tldp.org/LDP/abs/html/globbingref.html
• https://docs.oracle.com/javase/tutorial/essential/io/fileOps.html#glob