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3.5.8.1 Pattern Matching ¶Any character that appears in a pattern, other than the special pattern characters described below, matches itself. The NUL character may not occur in a pattern. A backslash escapes the following character; the escaping backslash is discarded when matching. The special pattern characters must be quoted if they are to be matched literally.
The special pattern characters have the following meanings:
*
Matches any string, including the null string. When the globstar shell option is enabled, and ‘*’ is used in a filename expansion context, two adjacent ‘*’s used as a single pattern match all files and zero or more directories and subdirectories. If followed by a ‘/’, two adjacent ‘*’s match only directories and subdirectories.
?
Matches any single character.
[…]
Matches any one of the characters enclosed between the brackets. This is known as a bracket expression and matches a single character. A pair of characters separated by a hyphen denotes a range expression; any character that falls between those two characters, inclusive, using the current locale’s collating sequence and character set, matches. If the first character following the ‘[’ is a ‘!’ or a ‘^’ then any character not within the range matches. To match a ‘−’, include it as the first or last character in the set. To match a ‘]’, include it as the first character in the set.
The sorting order of characters in range expressions, and the characters included in the range, are determined by the current locale and the values of the LC_COLLATE and LC_ALL shell variables, if set.
For example, in the default C locale, ‘[a-dx-z]’ is equivalent to ‘[abcdxyz]’. Many locales sort characters in dictionary order, and in these locales ‘[a-dx-z]’ is typically not equivalent to ‘[abcdxyz]’; it might be equivalent to ‘[aBbCcDdxYyZz]’, for example. To obtain the traditional interpretation of ranges in bracket expressions, you can force the use of the C locale by setting the LC_COLLATE or LC_ALL environment variable to the value ‘C’, or enable the globasciiranges shell option.
Within a bracket expression, character classes can be specified using the syntax [:class:], where class is one of the following classes defined in the POSIX standard:
alnum alpha ascii blank cntrl digit graph lower print punct space upper word xdigit
A character class matches any character belonging to that class. The word character class matches letters, digits, and the character ‘_’.
For instance, the following pattern will match any character belonging to the space character class in the current locale, then any upper case letter or ‘!’, a dot, and finally any lower case letter or a hyphen.
[[:space:]][[:upper:]!].[-[:lower:]]
Within a bracket expression, an equivalence class can be specified using the syntax [=c=], which matches all characters with the same collation weight (as defined by the current locale) as the character c.
Within a bracket expression, the syntax [.symbol.] matches the collating symbol symbol.
If the extglob shell option is enabled using the shopt builtin, the shell recognizes several extended pattern matching operators. In the following description, a pattern-list is a list of one or more patterns separated by a ‘|’. When matching filenames, the dotglob shell option determines the set of filenames that are tested, as described above. Composite patterns may be formed using one or more of the following sub-patterns:
?(pattern-list)
Matches zero or one occurrence of the given patterns.
*(pattern-list)
Matches zero or more occurrences of the given patterns.
+(pattern-list)
Matches one or more occurrences of the given patterns.
@(pattern-list)
Matches one of the given patterns.
!(pattern-list)
Matches anything except one of the given patterns.
The extglob option changes the behavior of the parser, since the parentheses are normally treated as operators with syntactic meaning. To ensure that extended matching patterns are parsed correctly, make sure that extglob is enabled before parsing constructs containing the patterns, including shell functions and command substitutions.
When matching filenames, the dotglob shell option determines the set of filenames that are tested: when dotglob is enabled, the set of filenames includes all files beginning with ‘.’, but the filenames . and .. must be matched by a pattern or sub-pattern that begins with a dot; when it is disabled, the set does not include any filenames beginning with ‘.’ unless the pattern or sub-pattern begins with a ‘.’. If the globskipdots shell option is enabled, the filenames . and .. never appear in the set. As above, ‘.’ only has a special meaning when matching filenames.
Complicated extended pattern matching against long strings is slow, especially when the patterns contain alternations and the strings contain multiple matches. Using separate matches against shorter strings, or using arrays of strings instead of a single long string, may be faster.
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