@c Copyright (C) 1994, 1996, 1998, 2000, 2001, 2003, 2004, 2005, 2006, 2007
@c Free Software Foundation, Inc.
-@c
+@c
@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.2 or
@c any later version published by the Free Software Foundation; with no
@subsection @samp{awk} regular expression syntax
-The character @samp{.} matches any single character except the null 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.
+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.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
matches a @samp{+}
@item \?
-matches a @samp{?}.
+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{\} can be used to quote the following character. 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 invalid. Within square brackets, @samp{\} can be used to quote the following character. Character classes are not supported, so for example you would need to use @samp{[0-9]} instead of @samp{[[: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.
+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.
+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 alternation operator is @samp{|}.
-The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+The characters @samp{^} and @samp{$} 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
+@item After an open-group, signified by
@samp{(}
@item After the alternation operator @samp{|}
-The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
+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
-The character @samp{.} matches any single character except newline.
+The character @samp{.} matches any single character except newline.
@table @samp
@item +
-indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
+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.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
matches a @samp{+}
@item \?
-matches a @samp{?}.
+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 ignored. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit. Non-matching lists @samp{[^@dots{}]} do not ever match newline.
+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. Non-matching lists @samp{[^@dots{}]} do not ever match newline.
GNU extensions are supported:
@enumerate
@end enumerate
-Grouping is performed with parentheses @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{(}.
+Grouping is performed with parentheses @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{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+The characters @samp{^} and @samp{$} 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 characters @samp{*}, @samp{+} and @samp{?} are special anywhere in a regular expression.
+The characters @samp{*}, @samp{+} and @samp{?} are special anywhere in a regular expression.
-The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
+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
-The character @samp{.} matches any single character except the null 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.
+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 + and ?
-match themselves.
+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.
+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{\(}.
+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 character @samp{^} only represents the beginning of a string when it appears:
@enumerate
-@item
+@item
At the beginning of a regular expression
-@item After an open-group, signified by
+@item After an open-group, signified by
@samp{\(}
@item After the alternation operator @samp{\|}
@item At the end of a regular expression
-@item Before a close-group, signified by
+@item Before a close-group, signified by
@samp{\)}
@item Before the alternation operator @samp{\|}
@item At the beginning of a regular expression
-@item After an open-group, signified by
+@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.
+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 emacs regular expression syntax
@subsection @samp{emacs} regular expression syntax
-The character @samp{.} matches any single character except newline.
+The character @samp{.} matches any single character except newline.
@table @samp
@item +
-indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
+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.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
matches a @samp{+}
@item \?
-matches a @samp{?}.
+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 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 not supported, so for example you would need to use @samp{[0-9]} instead of @samp{[[: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{\(}.
+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 character @samp{^} only represents the beginning of a string when it appears:
@enumerate
-@item
+@item
At the beginning of a regular expression
-@item After an open-group, signified by
+@item After an open-group, signified by
@samp{\(}
@item After the alternation operator @samp{\|}
@item At the end of a regular expression
-@item Before a close-group, signified by
+@item Before a close-group, signified by
@samp{\)}
@item Before the alternation operator @samp{\|}
@item At the beginning of a regular expression
-@item After an open-group, signified by
+@item After an open-group, signified by
@samp{\(}
@item After the alternation operator @samp{\|}
-The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
+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 gnu-awk regular expression syntax
@subsection @samp{gnu-awk} regular expression syntax
-The character @samp{.} matches any single character.
+The character @samp{.} matches any single character.
@table @samp
@item +
-indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
+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.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
matches a @samp{+}
@item \?
-matches a @samp{?}.
+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{\} can be used to quote the following character. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+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
@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 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 alternation operator is @samp{|}.
-The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+The characters @samp{^} and @samp{$} 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
+@item After an open-group, signified by
@samp{(}
@item After the alternation operator @samp{|}
-The longest possible match is returned; this applies to the regular expression as a whole and (subject to this constraint) to subexpressions within groups.
+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 grep regular expression syntax
@subsection @samp{grep} regular expression syntax
-The character @samp{.} matches any single character except newline.
+The character @samp{.} matches any single character except newline.
@table @samp
@item \+
-indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
+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 + and ?
-match themselves.
+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 ignored. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit. Non-matching lists @samp{[^@dots{}]} do not ever match newline.
+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. Non-matching lists @samp{[^@dots{}]} do not ever match newline.
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{\(}.
+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 character @samp{^} only represents the beginning of a string when it appears:
@enumerate
-@item
+@item
At the beginning of a regular expression
-@item After an open-group, signified by
+@item After an open-group, signified by
@samp{\(}
@item After a newline
@item At the end of a regular expression
-@item Before a close-group, signified by
+@item Before a close-group, signified by
@samp{\)}
@item Before a newline
@item At the beginning of a regular expression
-@item After an open-group, signified by
+@item After an open-group, signified by
@samp{\(}
@item After a newline
@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.
+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 posix-awk regular expression syntax
@subsection @samp{posix-awk} regular expression syntax
-The character @samp{.} matches any single character except the null 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.
+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.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
matches a @samp{+}
@item \?
-matches a @samp{?}.
+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{\} can be used to quote the following character. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit.
+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.
+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{(}.
+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 alternation operator is @samp{|}.
-The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+The characters @samp{^} and @samp{$} 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
+@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.
+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 posix-basic regular expression syntax
@subsection @samp{posix-egrep} regular expression syntax
-The character @samp{.} matches any single character except newline.
+The character @samp{.} matches any single character except newline.
@table @samp
@item +
-indicates that the regular expression should match one or more occurrences of the previous atom or regexp.
+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.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
matches a @samp{+}
@item \?
-matches a @samp{?}.
+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 ignored. Within square brackets, @samp{\} is taken literally. Character classes are supported; for example @samp{[[:digit:]]} will match a single decimal digit. Non-matching lists @samp{[^@dots{}]} do not ever match newline.
+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. Non-matching lists @samp{[^@dots{}]} do not ever match newline.
GNU extensions are supported:
@enumerate
@end enumerate
-Grouping is performed with parentheses @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{(}.
+Grouping is performed with parentheses @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{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+The characters @samp{^} and @samp{$} 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 characters @samp{*}, @samp{+} and @samp{?} are special anywhere in a regular expression.
+The characters @samp{*}, @samp{+} and @samp{?} are special anywhere in a regular expression.
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.
+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 posix-extended regular expression syntax
@subsection @samp{posix-extended} regular expression syntax
-The character @samp{.} matches any single character except the null 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.
+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.
+indicates that the regular expression should match zero or one occurrence of the previous atom or regexp.
@item \+
matches a @samp{+}
@item \?
-matches a @samp{?}.
+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.
+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 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 alternation operator is @samp{|}.
-The characters @samp{^} and @samp{$} always represent the beginning and end of a string respectively, except within square brackets. Within brackets, @samp{^} can be used to invert the membership of the character class being specified.
+The characters @samp{^} and @samp{$} 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
+@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.
+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 posix-minimal-basic regular expression syntax
@subsection @samp{posix-minimal-basic} regular expression syntax
-The character @samp{.} matches any single character except the null character.
+The character @samp{.} matches any single character except the null character.
-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.
+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{\(}.
+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 character @samp{^} only represents the beginning of a string when it appears:
@enumerate
-@item
+@item
At the beginning of a regular expression
-@item After an open-group, signified by
+@item After an open-group, signified by
@samp{\(}
@end enumerate
@item At the end of a regular expression
-@item Before a close-group, signified by
+@item Before a close-group, signified by
@samp{\)}
@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.
+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
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