Bash Patterns: Difference between revisions

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* [[bash Parameter and Variable Expansion]]
* [[bash Parameter and Variable Expansion]]
* [[Regular Expressions#Subjects|Regular Expressions]]
* [[Regular Expressions#Subjects|Regular Expressions]]
=Overview=
Bash patterns are a simple regular expression language defined by the [[#Metacharacters|metacharacters]] and rules described below.
Variable expansion can be used inside patterns:
<syntaxhighlight lang='bash'>
a="something"
b="some"
echo ${a#${b}}
</syntaxhighlight>
prints "thing".


=Metacharacters=
=Metacharacters=


The following characters have a special meaning when a bash pattern is evaluated, and they need to be escaped to be matched literally:
The following characters have a special meaning when a bash pattern is evaluated, and they need to be escaped to be matched literally:
==*==
&#42; (star) 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 will match all files and zero or more directories and subdirectories. If followed by a ‘/’, two adjacent ‘*’s will match only directories and subdirectories.
==?==
? (question mark) matches a single character. The dot ('.') is not a metacharacter.
==[...]==
Matches any one of the enclosed characters.
For example:
[- :]
matches '-', space and ':'.
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, is matched. A digit is matches as follows:
[0-9]
A ‘-’ may be matched by including it as the first or last character in the set.
A ‘]’ may be matched by including it as the first character in the set.
===Negation===
If the first character following the ‘[’ is a ‘!’ or a ‘^’ then any character not enclosed is matched. The match is for one character only.
To match a known number of characters, repeat the [!...] expression the known number of times. [!...]* does not work to match an undefined number of not-enclosed characters; it will match just one non-enclosed character then all the characters. This behavior is different than [[Sed_Regular_Expressions#Negation|sed behavior on negation]].
===Classes===
Within ‘[’ and ‘]’, 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: matches letters, digits, and the character ‘_’.
* xdigit
A character class matches any character belonging to that class.
==/==
To match a '/' (slash), use '\/'. If used in replacement constructs as [[Bash_Parameter_and_Variable_Expansion#Replace_Strings_in_Place|variable expansion replacement]], there is no need to escape slashes in the replacement string.
==~==
~ (tilda)
=='==
' (single quote) must be escaped to match:
\'
=="==
" (double quote) must be escaped to match:
\"
==;==
; (semicolon) must be escaped to match:
\;
==(...)==
Parentheses must be escaped to match
\(
\)
=Non-Special Characters=
These characters do not need to be escaped in bash patterns to match:
\ # forward slash
. # dot - does NOT match any character, it just matches a dot
: # column
=Paths=
See [[#.2F|/]] above.
=Pattern Lists=
<syntaxhighlight lang='bash'>
?(pattern-list)
</syntaxhighlight>
Matches zero or one occurrence of the given patterns.
<syntaxhighlight lang='bash'>
*(pattern-list)
</syntaxhighlight>
Matches zero or more occurrences of the given patterns.
<syntaxhighlight lang='bash'>
+(pattern-list)
</syntaxhighlight>
Matches one or more occurrences of the given patterns.
<syntaxhighlight lang='bash'>
@(pattern-list)
</syntaxhighlight>
Matches one of the given patterns.
<syntaxhighlight lang='bash'>
!(pattern-list)
</syntaxhighlight>
Matches anything except one of the given patterns.

Latest revision as of 18:11, 4 April 2021

External

Internal

Overview

Bash patterns are a simple regular expression language defined by the metacharacters and rules described below.

Variable expansion can be used inside patterns:

a="something"
b="some"
echo ${a#${b}}

prints "thing".

Metacharacters

The following characters have a special meaning when a bash pattern is evaluated, and they need to be escaped to be matched literally:

*

* (star) 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 will match all files and zero or more directories and subdirectories. If followed by a ‘/’, two adjacent ‘*’s will match only directories and subdirectories.

?

? (question mark) matches a single character. The dot ('.') is not a metacharacter.

[...]

Matches any one of the enclosed characters.

For example:

[- :]

matches '-', space and ':'.

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, is matched. A digit is matches as follows:

[0-9]

A ‘-’ may be matched by including it as the first or last character in the set.

A ‘]’ may be matched by including it as the first character in the set.

Negation

If the first character following the ‘[’ is a ‘!’ or a ‘^’ then any character not enclosed is matched. The match is for one character only.

To match a known number of characters, repeat the [!...] expression the known number of times. [!...]* does not work to match an undefined number of not-enclosed characters; it will match just one non-enclosed character then all the characters. This behavior is different than sed behavior on negation.

Classes

Within ‘[’ and ‘]’, 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: matches letters, digits, and the character ‘_’.
  • xdigit

A character class matches any character belonging to that class.

/

To match a '/' (slash), use '\/'. If used in replacement constructs as variable expansion replacement, there is no need to escape slashes in the replacement string.

~

~ (tilda)

'

' (single quote) must be escaped to match:

\'

"

" (double quote) must be escaped to match:

\"

;

(semicolon) must be escaped to match
\;


(...)

Parentheses must be escaped to match

\(
\)

Non-Special Characters

These characters do not need to be escaped in bash patterns to match:

\ # forward slash
. # dot - does NOT match any character, it just matches a dot
: # column

Paths

See / above.

Pattern Lists

?(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.