-@c Copyright (C) 1994, 1996, 1998, 2000--2001, 2003--2007, 2009--2025 Free
-@c Software Foundation, Inc.
+@c Copyright (C) 1994--2025 Free Software Foundation, Inc.
@c
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
-@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
-@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>.
+@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
+@c A copy of the license is included in the ``GNU Free
+@c Documentation License'' file as part of this distribution.
@c this regular expression description is for: generic
@menu
* awk regular expression syntax::
-* egrep regular expression syntax::
* ed regular expression syntax::
+* egrep regular expression syntax::
* emacs regular expression syntax::
* gnu-awk regular expression syntax::
* grep regular expression syntax::
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} can be used to quote the following character. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are not supported and so @samp{\w}, @samp{\W}, @samp{\<}, @samp{\>}, @samp{\b}, @samp{\B}, @samp{\`}, and @samp{\'} match @samp{w}, @samp{W}, @samp{<}, @samp{>}, @samp{b}, @samp{B}, @samp{`}, and @samp{'} respectively.
+
Grouping is performed with parentheses @samp{()}. An unmatched @samp{)} matches just itself. A backslash followed by a digit matches that digit.
The alternation operator is @samp{|}.
The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+
@samp{*}, @samp{+} and @samp{?} are special at any point in a regular expression except:
@enumerate
@item At the beginning of a regular expression
-@item After an open-group, signified by
-@samp{(}
+@item After an open-group, signified by @samp{(}
+
@item After the alternation operator @samp{|}
@end enumerate
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
-@node egrep regular expression syntax
-@subsection @samp{egrep} regular expression syntax
+@node ed regular expression syntax
+@subsection @samp{ed} regular expression syntax
-The character @samp{.} matches any single character.
+The character @samp{.} matches any single character except the null character.
@table @samp
-@item +
-indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
-@item ?
-indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
-matches a @samp{+}
+indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
@item \?
-matches a @samp{?}.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
+@item + and ?
+match themselves.
+
@end table
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are supported:
@enumerate
@end enumerate
-Grouping is performed with parentheses @samp{()}. An unmatched @samp{)} matches just itself. A backslash followed by a digit acts as a back-reference and matches the same thing as the previous grouped expression indicated by that number. For example @samp{\2} matches the second group expression. The order of group expressions is determined by the position of their opening parenthesis @samp{(}.
+Grouping is performed with backslashes followed by parentheses @samp{\(}, @samp{\)}. A backslash followed by a digit acts as a back-reference and matches the same thing as the previous grouped expression indicated by that number. For example @samp{\2} matches the second group expression. The order of group expressions is determined by the position of their opening parenthesis @samp{\(}.
-The alternation operator is @samp{|}.
+The alternation operator is @samp{\|}.
-The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+The character @samp{^} only represents the beginning of a string when it appears:
+@enumerate
-The characters @samp{*}, @samp{+} and @samp{?} are special anywhere in a regular expression.
+@item At the beginning of a regular expression
+
+@item After an open-group, signified by @samp{\(}
+
+
+@item After the alternation operator @samp{\|}
+
+@end enumerate
+
+
+The character @samp{$} only represents the end of a string when it appears:
+@enumerate
+
+@item At the end of a regular expression
+
+@item Before a close-group, signified by @samp{\)}
+
+@item Before the alternation operator @samp{\|}
+
+@end enumerate
+
+
+@samp{\*}, @samp{\+} and @samp{\?} are special at any point in a regular expression except:
+@enumerate
+
+@item At the beginning of a regular expression
+
+@item After an open-group, signified by @samp{\(}
+
+@item After the alternation operator @samp{\|}
+
+@end enumerate
+
+
+Intervals are specified by @samp{\@{} and @samp{\@}}.
+Invalid intervals such as @samp{a\@{1z} are not accepted.
-Intervals are specified by @samp{@{} and @samp{@}}. Invalid intervals are treated as literals, for example @samp{a@{1} is treated as @samp{a\@{1}
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
-@node ed regular expression syntax
-@subsection @samp{ed} regular expression syntax
+@node egrep regular expression syntax
+@subsection @samp{egrep} regular expression syntax
-The character @samp{.} matches any single character except the null character.
+The character @samp{.} matches any single character.
@table @samp
-@item \+
+@item +
indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
-@item \?
+@item ?
indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
-@item + and ?
-match themselves.
+@item \+
+matches a @samp{+}
+@item \?
+matches a @samp{?}.
@end table
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are supported:
@enumerate
@end enumerate
-Grouping is performed with backslashes followed by parentheses @samp{\(}, @samp{\)}. A backslash followed by a digit acts as a back-reference and matches the same thing as the previous grouped expression indicated by that number. For example @samp{\2} matches the second group expression. The order of group expressions is determined by the position of their opening parenthesis @samp{\(}.
-
-The alternation operator is @samp{\|}.
-
-The character @samp{^} only represents the beginning of a string when it appears:
-@enumerate
-
-@item
-At the beginning of a regular expression
-
-@item After an open-group, signified by
-@samp{\(}
-
-@item After the alternation operator @samp{\|}
-
-@end enumerate
-
-
-The character @samp{$} only represents the end of a string when it appears:
-@enumerate
-
-@item At the end of a regular expression
-
-@item Before a close-group, signified by
-@samp{\)}
-@item Before the alternation operator @samp{\|}
-
-@end enumerate
-
+Grouping is performed with parentheses @samp{()}. An unmatched @samp{)} matches just itself. A backslash followed by a digit acts as a back-reference and matches the same thing as the previous grouped expression indicated by that number. For example @samp{\2} matches the second group expression. The order of group expressions is determined by the position of their opening parenthesis @samp{(}.
-@samp{\*}, @samp{\+} and @samp{\?} are special at any point in a regular expression except:
-@enumerate
+The alternation operator is @samp{|}.
-@item At the beginning of a regular expression
+The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
-@item After an open-group, signified by
-@samp{\(}
-@item After the alternation operator @samp{\|}
-@end enumerate
+The characters @samp{*}, @samp{+} and @samp{?} are special anywhere in a regular expression.
-Intervals are specified by @samp{\@{} and @samp{\@}}. Invalid intervals such as @samp{a\@{1z} are not accepted.
+Intervals are specified by @samp{@{} and @samp{@}}.
+Invalid intervals are treated as literals, for example @samp{a@{1} is treated as @samp{a\@{1}
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
@end table
-Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are ignored. Within square brackets, @samp{\} is taken literally. Character classes are not supported, so for example you would need to use @samp{[0-9]} instead of @samp{[[:digit:]]}.
+Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are ignored. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are supported:
@enumerate
The character @samp{^} only represents the beginning of a string when it appears:
@enumerate
-@item
-At the beginning of a regular expression
+@item At the beginning of a regular expression
+
+@item After an open-group, signified by @samp{\(}
-@item After an open-group, signified by
-@samp{\(}
@item After the alternation operator @samp{\|}
@item At the end of a regular expression
-@item Before a close-group, signified by
-@samp{\)}
+@item Before a close-group, signified by @samp{\)}
+
@item Before the alternation operator @samp{\|}
@end enumerate
@item At the beginning of a regular expression
-@item After an open-group, signified by
-@samp{\(}
+@item After an open-group, signified by @samp{\(}
+
@item After the alternation operator @samp{\|}
@end enumerate
+Intervals are specified by @samp{\@{} and @samp{\@}}.
+Invalid intervals such as @samp{a\@{1z} are not accepted.
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} can be used to quote the following character. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are supported:
@enumerate
The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+
@samp{*}, @samp{+} and @samp{?} are special at any point in a regular expression except:
@enumerate
@item At the beginning of a regular expression
-@item After an open-group, signified by
-@samp{(}
+@item After an open-group, signified by @samp{(}
+
@item After the alternation operator @samp{|}
@end enumerate
-Intervals are specified by @samp{@{} and @samp{@}}. Invalid intervals are treated as literals, for example @samp{a@{1} is treated as @samp{a\@{1}
+Intervals are specified by @samp{@{} and @samp{@}}.
+Invalid intervals are treated as literals, for example @samp{a@{1} is treated as @samp{a\@{1}
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item + and ?
match themselves.
+
@end table
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are supported:
@enumerate
The character @samp{^} only represents the beginning of a string when it appears:
@enumerate
-@item
-At the beginning of a regular expression
+@item At the beginning of a regular expression
+
+@item After an open-group, signified by @samp{\(}
-@item After an open-group, signified by
-@samp{\(}
@item After a newline
@item At the end of a regular expression
-@item Before a close-group, signified by
-@samp{\)}
+@item Before a close-group, signified by @samp{\)}
+
@item Before a newline
@item Before the alternation operator @samp{\|}
@item At the beginning of a regular expression
-@item After an open-group, signified by
-@samp{\(}
+@item After an open-group, signified by @samp{\(}
+
@item After a newline
@item After the alternation operator @samp{\|}
@end enumerate
-Intervals are specified by @samp{\@{} and @samp{\@}}. Invalid intervals such as @samp{a\@{1z} are not accepted.
+Intervals are specified by @samp{\@{} and @samp{\@}}.
+Invalid intervals such as @samp{a\@{1z} are not accepted.
+
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} can be used to quote the following character. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are not supported and so @samp{\w}, @samp{\W}, @samp{\<}, @samp{\>}, @samp{\b}, @samp{\B}, @samp{\`}, and @samp{\'} match @samp{w}, @samp{W}, @samp{<}, @samp{>}, @samp{b}, @samp{B}, @samp{`}, and @samp{'} respectively.
+
Grouping is performed with parentheses @samp{()}. An unmatched @samp{)} matches just itself. A backslash followed by a digit acts as a back-reference and matches the same thing as the previous grouped expression indicated by that number. For example @samp{\2} matches the second group expression. The order of group expressions is determined by the position of their opening parenthesis @samp{(}.
The alternation operator is @samp{|}.
The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+
@samp{*}, @samp{+} and @samp{?} are special at any point in a regular expression except the following places, where they are not allowed:
@enumerate
@item At the beginning of a regular expression
-@item After an open-group, signified by
-@samp{(}
+@item After an open-group, signified by @samp{(}
+
@item After the alternation operator @samp{|}
@end enumerate
-Intervals are specified by @samp{@{} and @samp{@}}. Invalid intervals are treated as literals, for example @samp{a@{1} is treated as @samp{a\@{1}
+Intervals are specified by @samp{@{} and @samp{@}}.
+Invalid intervals are treated as literals, for example @samp{a@{1} is treated as @samp{a\@{1}
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are supported:
@enumerate
The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+
@samp{*}, @samp{+} and @samp{?} are special at any point in a regular expression except the following places, where they are not allowed:
@enumerate
@item At the beginning of a regular expression
-@item After an open-group, signified by
-@samp{(}
+@item After an open-group, signified by @samp{(}
+
@item After the alternation operator @samp{|}
@end enumerate
-Intervals are specified by @samp{@{} and @samp{@}}. Invalid intervals such as @samp{a@{1z} are not accepted.
+Intervals are specified by @samp{@{} and @samp{@}}.
+Invalid intervals such as @samp{a@{1z} are not accepted.
+
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
Bracket expressions are used to match ranges of characters. Bracket expressions where the range is backward, for example @samp{[z-a]}, are invalid. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+
GNU extensions are supported:
@enumerate
The character @samp{^} only represents the beginning of a string when it appears:
@enumerate
-@item
-At the beginning of a regular expression
+@item At the beginning of a regular expression
+
+@item After an open-group, signified by @samp{\(}
-@item After an open-group, signified by
-@samp{\(}
@end enumerate
@item At the end of a regular expression
-@item Before a close-group, signified by
-@samp{\)}
+@item Before a close-group, signified by @samp{\)}
+
@end enumerate
-Intervals are specified by @samp{\@{} and @samp{\@}}. Invalid intervals such as @samp{a\@{1z} are not accepted.
+Intervals are specified by @samp{\@{} and @samp{\@}}.
+Invalid intervals such as @samp{a\@{1z} are not accepted.
+
The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
@node sed regular expression syntax
@subsection @samp{sed} regular expression syntax
-This is a synonym for ed.
+This is a synonym for ed.
\ No newline at end of file
projects / thirdparty / gnulib.git / commitdiff
