Package: regexp/syntax

package syntax Import Path regexp/syntax (on go.dev) Dependency Relation imports 6 packages, and imported by one package

Involved Source Files compile.go d doc.go Package syntax parses regular expressions into parse trees and compiles parse trees into programs. Most clients of regular expressions will use the facilities of package [regexp] (such as [regexp.Compile] and [regexp.Match]) instead of this package. # Syntax The regular expression syntax understood by this package when parsing with the [Perl] flag is as follows. Parts of the syntax can be disabled by passing alternate flags to [Parse]. Single characters: . any character, possibly including newline (flag s=true) [xyz] character class [^xyz] negated character class \d Perl character class \D negated Perl character class [[:alpha:]] ASCII character class [[:^alpha:]] negated ASCII character class \pN Unicode character class (one-letter name) \p{Greek} Unicode character class \PN negated Unicode character class (one-letter name) \P{Greek} negated Unicode character class Composites: xy x followed by y x|y x or y (prefer x) Repetitions: x* zero or more x, prefer more x+ one or more x, prefer more x? zero or one x, prefer one x{n,m} n or n+1 or ... or m x, prefer more x{n,} n or more x, prefer more x{n} exactly n x x*? zero or more x, prefer fewer x+? one or more x, prefer fewer x?? zero or one x, prefer zero x{n,m}? n or n+1 or ... or m x, prefer fewer x{n,}? n or more x, prefer fewer x{n}? exactly n x Implementation restriction: The counting forms x{n,m}, x{n,}, and x{n} reject forms that create a minimum or maximum repetition count above 1000. Unlimited repetitions are not subject to this restriction. Grouping: (re) numbered capturing group (submatch) (?P<name>re) named & numbered capturing group (submatch) (?<name>re) named & numbered capturing group (submatch) (?:re) non-capturing group (?flags) set flags within current group; non-capturing (?flags:re) set flags during re; non-capturing Flag syntax is xyz (set) or -xyz (clear) or xy-z (set xy, clear z). The flags are: i case-insensitive (default false) m multi-line mode: ^ and $ match begin/end line in addition to begin/end text (default false) s let . match \n (default false) U ungreedy: swap meaning of x* and x*?, x+ and x+?, etc (default false) Empty strings: ^ at beginning of text or line (flag m=true) $ at end of text (like \z not \Z) or line (flag m=true) \A at beginning of text \b at ASCII word boundary (\w on one side and \W, \A, or \z on the other) \B not at ASCII word boundary \z at end of text Escape sequences: \a bell (== \007) \f form feed (== \014) \t horizontal tab (== \011) \n newline (== \012) \r carriage return (== \015) \v vertical tab character (== \013) \* literal *, for any punctuation character * \123 octal character code (up to three digits) \x7F hex character code (exactly two digits) \x{10FFFF} hex character code \Q...\E literal text ... even if ... has punctuation Character class elements: x single character A-Z character range (inclusive) \d Perl character class [:foo:] ASCII character class foo \p{Foo} Unicode character class Foo \pF Unicode character class F (one-letter name) Named character classes as character class elements: [\d] digits (== \d) [^\d] not digits (== \D) [\D] not digits (== \D) [^\D] not not digits (== \d) [[:name:]] named ASCII class inside character class (== [:name:]) [^[:name:]] named ASCII class inside negated character class (== [:^name:]) [\p{Name}] named Unicode property inside character class (== \p{Name}) [^\p{Name}] named Unicode property inside negated character class (== \P{Name}) Perl character classes (all ASCII-only): \d digits (== [0-9]) \D not digits (== [^0-9]) \s whitespace (== [\t\n\f\r ]) \S not whitespace (== [^\t\n\f\r ]) \w word characters (== [0-9A-Za-z_]) \W not word characters (== [^0-9A-Za-z_]) ASCII character classes: [[:alnum:]] alphanumeric (== [0-9A-Za-z]) [[:alpha:]] alphabetic (== [A-Za-z]) [[:ascii:]] ASCII (== [\x00-\x7F]) [[:blank:]] blank (== [\t ]) [[:cntrl:]] control (== [\x00-\x1F\x7F]) [[:digit:]] digits (== [0-9]) [[:graph:]] graphical (== [!-~] == [A-Za-z0-9!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~]) [[:lower:]] lower case (== [a-z]) [[:print:]] printable (== [ -~] == [ [:graph:]]) [[:punct:]] punctuation (== [!-/:-@[-`{-~]) [[:space:]] whitespace (== [\t\n\v\f\r ]) [[:upper:]] upper case (== [A-Z]) [[:word:]] word characters (== [0-9A-Za-z_]) [[:xdigit:]] hex digit (== [0-9A-Fa-f]) Unicode character classes are those in [unicode.Categories] and [unicode.Scripts]. op_string.go parse.go perl_groups.go prog.go regexp.go simplify.go

Package-Level Functions (total 4)

func Compile(re *Regexp) (*Prog, error) Compile compiles the regexp into a program to be executed. The regexp should have been simplified already (returned from re.Simplify).

func EmptyOpContext(r1, r2 rune) EmptyOp EmptyOpContext returns the zero-width assertions satisfied at the position between the runes r1 and r2. Passing r1 == -1 indicates that the position is at the beginning of the text. Passing r2 == -1 indicates that the position is at the end of the text.

func IsWordChar(r rune) bool IsWordChar reports whether r is considered a “word character” during the evaluation of the \b and \B zero-width assertions. These assertions are ASCII-only: the word characters are [A-Za-z0-9_].

func Parse(s string, flags Flags) (*Regexp, error) Parse parses a regular expression string s, controlled by the specified Flags, and returns a regular expression parse tree. The syntax is described in the top-level comment.

Package-Level Constants (total 65)

const ClassNL Flags = 4 // allow character classes like [^a-z] and [[:space:]] to match newline

const DotNL Flags = 8 // allow . to match newline

const EmptyBeginLine EmptyOp = 1

const EmptyBeginText EmptyOp = 4

const EmptyEndLine EmptyOp = 2

const EmptyEndText EmptyOp = 8

const EmptyNoWordBoundary EmptyOp = 32

const EmptyWordBoundary EmptyOp = 16

const ErrInternalError ErrorCode = "regexp/syntax: internal error" Unexpected error

const ErrInvalidCharClass ErrorCode = "invalid character class" Parse errors

const ErrInvalidCharRange ErrorCode = "invalid character class range"