ref: 382c9ef92cf0830f5639906ffd5f363ecefd670a
dir: /sys/man/6/regexp/
.TH REGEXP 6 .SH NAME regexp \- regular expression notation .SH DESCRIPTION A .I "regular expression" specifies a set of strings of characters. A member of this set of strings is said to be .I matched by the regular expression. In many applications a delimiter character, commonly .LR / , bounds a regular expression. In the following specification for regular expressions the word `character' means any character (rune) but newline. .PP The syntax for a regular expression .B e0 is .IP .EX e3: literal | charclass | '.' | '^' | '$' | '(' e0 ')' e2: e3 | e2 REP REP: '*' | '+' | '?' e1: e2 | e1 e2 e0: e1 | e0 '|' e1 .EE .PP A .B literal is any non-metacharacter, or a metacharacter (one of .BR .*+?[]()|\e^$ ), or the delimiter preceded by .LR \e . .PP A .B charclass is a nonempty string .I s bracketed .BI [ \|s\| ] (or .BI [^ s\| ]\fR); it matches any character in (or not in) .IR s . A negated character class never matches newline. A substring .IB a - b\f1, with .I a and .I b in ascending order, stands for the inclusive range of characters between .I a and .IR b . In .IR s , the metacharacters .LR - , .LR ] , an initial .LR ^ , and the regular expression delimiter must be preceded by a .LR \e ; other metacharacters have no special meaning and may appear unescaped. .PP A .L . matches any character. .PP A .L ^ matches the beginning of a line; .L $ matches the end of the line. .PP The .B REP operators match zero or more .RB ( * ), one or more .RB ( + ), zero or one .RB ( ? ), instances respectively of the preceding regular expression .BR e2 . .PP A concatenated regular expression, .BR "e1\|e2" , matches a match to .B e1 followed by a match to .BR e2 . .PP An alternative regular expression, .BR "e0\||\|e1" , matches either a match to .B e0 or a match to .BR e1 . .PP A match to any part of a regular expression extends as far as possible without preventing a match to the remainder of the regular expression. .SH "SEE ALSO" .IR awk (1), .IR ed (1), .IR grep (1), .IR sam (1), .IR sed (1), .IR regexp (2)