Source: regexp.go in package regexp

Package regexp implements regular expression search. The syntax of the regular expressions accepted is the same general syntax used by Perl, Python, and other languages. More precisely, it is the syntax accepted by RE2 and described at https://golang.org/s/re2syntax, except for \C. For an overview of the syntax, run go doc regexp/syntax The regexp implementation provided by this package is guaranteed to run in time linear in the size of the input. (This is a property not guaranteed by most open source implementations of regular expressions.) For more information about this property, see https://swtch.com/~rsc/regexp/regexp1.html or any book about automata theory. All characters are UTF-8-encoded code points. There are 16 methods of Regexp that match a regular expression and identify the matched text. Their names are matched by this regular expression: Find(All)?(String)?(Submatch)?(Index)? If 'All' is present, the routine matches successive non-overlapping matches of the entire expression. Empty matches abutting a preceding match are ignored. The return value is a slice containing the successive return values of the corresponding non-'All' routine. These routines take an extra integer argument, n. If n >= 0, the function returns at most n matches/submatches; otherwise, it returns all of them. If 'String' is present, the argument is a string; otherwise it is a slice of bytes; return values are adjusted as appropriate. If 'Submatch' is present, the return value is a slice identifying the successive submatches of the expression. Submatches are matches of parenthesized subexpressions (also known as capturing groups) within the regular expression, numbered from left to right in order of opening parenthesis. Submatch 0 is the match of the entire expression, submatch 1 the match of the first parenthesized subexpression, and so on. If 'Index' is present, matches and submatches are identified by byte index pairs within the input string: result[2*n:2*n+1] identifies the indexes of the nth submatch. The pair for n==0 identifies the match of the entire expression. If 'Index' is not present, the match is identified by the text of the match/submatch. If an index is negative or text is nil, it means that subexpression did not match any string in the input. For 'String' versions an empty string means either no match or an empty match. There is also a subset of the methods that can be applied to text read from a RuneReader: MatchReader, FindReaderIndex, FindReaderSubmatchIndex This set may grow. Note that regular expression matches may need to examine text beyond the text returned by a match, so the methods that match text from a RuneReader may read arbitrarily far into the input before returning. (There are a few other methods that do not match this pattern.)

package regexp

import (
	"bytes"
	"io"
	"regexp/syntax"
	"strconv"
	"strings"
	"sync"
	"unicode"
	"unicode/utf8"
)

Regexp is the representation of a compiled regular expression. A Regexp is safe for concurrent use by multiple goroutines, except for configuration methods, such as Longest.

type Regexp struct {
	expr           string       // as passed to Compile
	prog           *syntax.Prog // compiled program
	onepass        *onePassProg // onepass program or nil
	numSubexp      int
	maxBitStateLen int
	subexpNames    []string
	prefix         string         // required prefix in unanchored matches
	prefixBytes    []byte         // prefix, as a []byte
	prefixRune     rune           // first rune in prefix
	prefixEnd      uint32         // pc for last rune in prefix
	mpool          int            // pool for machines
	matchcap       int            // size of recorded match lengths
	prefixComplete bool           // prefix is the entire regexp
	cond           syntax.EmptyOp // empty-width conditions required at start of match
	minInputLen    int            // minimum length of the input in bytes

This field can be modified by the Longest method, but it is otherwise read-only.

	longest bool // whether regexp prefers leftmost-longest match
}

String returns the source text used to compile the regular expression.

func (re *Regexp) String() string {
	return re.expr
}

Copy returns a new Regexp object copied from re. Calling Longest on one copy does not affect another. Deprecated: In earlier releases, when using a Regexp in multiple goroutines, giving each goroutine its own copy helped to avoid lock contention. As of Go 1.12, using Copy is no longer necessary to avoid lock contention. Copy may still be appropriate if the reason for its use is to make two copies with different Longest settings.

func (re *Regexp) Copy() *Regexp {
	re2 := *re
	return &re2
}

Compile parses a regular expression and returns, if successful, a Regexp object that can be used to match against text. When matching against text, the regexp returns a match that begins as early as possible in the input (leftmost), and among those it chooses the one that a backtracking search would have found first. This so-called leftmost-first matching is the same semantics that Perl, Python, and other implementations use, although this package implements it without the expense of backtracking. For POSIX leftmost-longest matching, see CompilePOSIX.

func Compile(expr string) (*Regexp, error) {
	return compile(expr, syntax.Perl, false)
}

CompilePOSIX is like Compile but restricts the regular expression to POSIX ERE (egrep) syntax and changes the match semantics to leftmost-longest. That is, when matching against text, the regexp returns a match that begins as early as possible in the input (leftmost), and among those it chooses a match that is as long as possible. This so-called leftmost-longest matching is the same semantics that early regular expression implementations used and that POSIX specifies. However, there can be multiple leftmost-longest matches, with different submatch choices, and here this package diverges from POSIX. Among the possible leftmost-longest matches, this package chooses the one that a backtracking search would have found first, while POSIX specifies that the match be chosen to maximize the length of the first subexpression, then the second, and so on from left to right. The POSIX rule is computationally prohibitive and not even well-defined. See https://swtch.com/~rsc/regexp/regexp2.html#posix for details.

func CompilePOSIX(expr string) (*Regexp, error) {
	return compile(expr, syntax.POSIX, true)
}

Longest makes future searches prefer the leftmost-longest match. That is, when matching against text, the regexp returns a match that begins as early as possible in the input (leftmost), and among those it chooses a match that is as long as possible. This method modifies the Regexp and may not be called concurrently with any other methods.

func (re *Regexp) Longest() {
	re.longest = true
}

func compile(expr string, mode syntax.Flags, longest bool) (*Regexp, error) {
	re, err := syntax.Parse(expr, mode)
	if err != nil {
		return nil, err
	}
	maxCap := re.MaxCap()
	capNames := re.CapNames()

	re = re.Simplify()
	prog, err := syntax.Compile(re)
	if err != nil {
		return nil, err
	}
	matchcap := prog.NumCap
	if matchcap < 2 {
		matchcap = 2
	}
	regexp := &Regexp{
		expr:        expr,
		prog:        prog,
		onepass:     compileOnePass(prog),
		numSubexp:   maxCap,
		subexpNames: capNames,
		cond:        prog.StartCond(),
		longest:     longest,
		matchcap:    matchcap,
		minInputLen: minInputLen(re),
	}
	if regexp.onepass == nil {
		regexp.prefix, regexp.prefixComplete = prog.Prefix()
		regexp.maxBitStateLen = maxBitStateLen(prog)
	} else {
		regexp.prefix, regexp.prefixComplete, regexp.prefixEnd = onePassPrefix(prog)
	}

TODO(rsc): Remove this allocation by adding IndexString to package bytes.

		regexp.prefixBytes = []byte(regexp.prefix)
		regexp.prefixRune, _ = utf8.DecodeRuneInString(regexp.prefix)
	}

	n := len(prog.Inst)
	i := 0
	for matchSize[i] != 0 && matchSize[i] < n {
		i++
	}
	regexp.mpool = i

	return regexp, nil
}

Pools of *machine for use during (*Regexp).doExecute, split up by the size of the execution queues. matchPool[i] machines have queue size matchSize[i]. On a 64-bit system each queue entry is 16 bytes, so matchPool[0] has 16*2*128 = 4kB queues, etc. The final matchPool is a catch-all for very large queues.

var (
	matchSize = [...]int{128, 512, 2048, 16384, 0}
	matchPool [len(matchSize)]sync.Pool
)

get returns a machine to use for matching re. It uses the re's machine cache if possible, to avoid unnecessary allocation.

func (re *Regexp) get() *machine {
	m, ok := matchPool[re.mpool].Get().(*machine)
	if !ok {
		m = new(machine)
	}
	m.re = re
	m.p = re.prog
	if cap(m.matchcap) < re.matchcap {
		m.matchcap = make([]int, re.matchcap)
		for _, t := range m.pool {
			t.cap = make([]int, re.matchcap)
		}
	}

Allocate queues if needed. Or reallocate, for "large" match pool.

	n := matchSize[re.mpool]
	if n == 0 { // large pool
		n = len(re.prog.Inst)
	}
	if len(m.q0.sparse) < n {
		m.q0 = queue{make([]uint32, n), make([]entry, 0, n)}
		m.q1 = queue{make([]uint32, n), make([]entry, 0, n)}
	}
	return m
}

put returns a machine to the correct machine pool.

func (re *Regexp) put(m *machine) {
	m.re = nil
	m.p = nil
	m.inputs.clear()
	matchPool[re.mpool].Put(m)
}

minInputLen walks the regexp to find the minimum length of any matchable input

func minInputLen(re *syntax.Regexp) int {
	switch re.Op {
	default:
		return 0
	case syntax.OpAnyChar, syntax.OpAnyCharNotNL, syntax.OpCharClass:
		return 1
	case syntax.OpLiteral:
		l := 0
		for _, r := range re.Rune {
			l += utf8.RuneLen(r)
		}
		return l
	case syntax.OpCapture, syntax.OpPlus:
		return minInputLen(re.Sub[0])
	case syntax.OpRepeat:
		return re.Min * minInputLen(re.Sub[0])
	case syntax.OpConcat:
		l := 0
		for _, sub := range re.Sub {
			l += minInputLen(sub)
		}
		return l
	case syntax.OpAlternate:
		l := minInputLen(re.Sub[0])
		var lnext int
		for _, sub := range re.Sub[1:] {
			lnext = minInputLen(sub)
			if lnext < l {
				l = lnext
			}
		}
		return l
	}
}

MustCompile is like Compile but panics if the expression cannot be parsed. It simplifies safe initialization of global variables holding compiled regular expressions.

func MustCompile(str string) *Regexp {
	regexp, err := Compile(str)
	if err != nil {
		panic(`regexp: Compile(` + quote(str) + `): ` + err.Error())
	}
	return regexp
}

MustCompilePOSIX is like CompilePOSIX but panics if the expression cannot be parsed. It simplifies safe initialization of global variables holding compiled regular expressions.

func MustCompilePOSIX(str string) *Regexp {
	regexp, err := CompilePOSIX(str)
	if err != nil {
		panic(`regexp: CompilePOSIX(` + quote(str) + `): ` + err.Error())
	}
	return regexp
}

func quote(s string) string {
	if strconv.CanBackquote(s) {
		return "`" + s + "`"
	}
	return strconv.Quote(s)
}

NumSubexp returns the number of parenthesized subexpressions in this Regexp.

func (re *Regexp) NumSubexp() int {
	return re.numSubexp
}

SubexpNames returns the names of the parenthesized subexpressions in this Regexp. The name for the first sub-expression is names[1], so that if m is a match slice, the name for m[i] is SubexpNames()[i]. Since the Regexp as a whole cannot be named, names[0] is always the empty string. The slice should not be modified.

func (re *Regexp) SubexpNames() []string {
	return re.subexpNames
}

SubexpIndex returns the index of the first subexpression with the given name, or -1 if there is no subexpression with that name. Note that multiple subexpressions can be written using the same name, as in (?P<bob>a+)(?P<bob>b+), which declares two subexpressions named "bob". In this case, SubexpIndex returns the index of the leftmost such subexpression in the regular expression.

func (re *Regexp) SubexpIndex(name string) int {
	if name != "" {
		for i, s := range re.subexpNames {
			if name == s {
				return i
			}
		}
	}
	return -1
}

const endOfText rune = -1

input abstracts different representations of the input text. It provides one-character lookahead.

type input interface {
	step(pos int) (r rune, width int) // advance one rune
	canCheckPrefix() bool             // can we look ahead without losing info?
	hasPrefix(re *Regexp) bool
	index(re *Regexp, pos int) int
	context(pos int) lazyFlag
}

inputString scans a string.

type inputString struct {
	str string
}

func (i *inputString) step(pos int) (rune, int) {
	if pos < len(i.str) {
		c := i.str[pos]
		if c < utf8.RuneSelf {
			return rune(c), 1
		}
		return utf8.DecodeRuneInString(i.str[pos:])
	}
	return endOfText, 0
}

func (i *inputString) canCheckPrefix() bool {
	return true
}

func (i *inputString) hasPrefix(re *Regexp) bool {
	return strings.HasPrefix(i.str, re.prefix)
}

func (i *inputString) index(re *Regexp, pos int) int {
	return strings.Index(i.str[pos:], re.prefix)
}

func (i *inputString) context(pos int) lazyFlag {

0 < pos && pos <= len(i.str)

	if uint(pos-1) < uint(len(i.str)) {
		r1 = rune(i.str[pos-1])
		if r1 >= utf8.RuneSelf {
			r1, _ = utf8.DecodeLastRuneInString(i.str[:pos])
		}

0 <= pos && pos < len(i.str)

	if uint(pos) < uint(len(i.str)) {
		r2 = rune(i.str[pos])
		if r2 >= utf8.RuneSelf {
			r2, _ = utf8.DecodeRuneInString(i.str[pos:])
		}
	}
	return newLazyFlag(r1, r2)
}

inputBytes scans a byte slice.

type inputBytes struct {
	str []byte
}

func (i *inputBytes) step(pos int) (rune, int) {
	if pos < len(i.str) {
		c := i.str[pos]
		if c < utf8.RuneSelf {
			return rune(c), 1
		}
		return utf8.DecodeRune(i.str[pos:])
	}
	return endOfText, 0
}

func (i *inputBytes) canCheckPrefix() bool {
	return true
}

func (i *inputBytes) hasPrefix(re *Regexp) bool {
	return bytes.HasPrefix(i.str, re.prefixBytes)
}

func (i *inputBytes) index(re *Regexp, pos int) int {
	return bytes.Index(i.str[pos:], re.prefixBytes)
}

func (i *inputBytes) context(pos int) lazyFlag {

0 < pos && pos <= len(i.str)

	if uint(pos-1) < uint(len(i.str)) {
		r1 = rune(i.str[pos-1])
		if r1 >= utf8.RuneSelf {
			r1, _ = utf8.DecodeLastRune(i.str[:pos])
		}

0 <= pos && pos < len(i.str)

	if uint(pos) < uint(len(i.str)) {
		r2 = rune(i.str[pos])
		if r2 >= utf8.RuneSelf {
			r2, _ = utf8.DecodeRune(i.str[pos:])
		}
	}
	return newLazyFlag(r1, r2)
}

inputReader scans a RuneReader.

type inputReader struct {
	r     io.RuneReader
	atEOT bool
	pos   int
}

func (i *inputReader) step(pos int) (rune, int) {
	if !i.atEOT && pos != i.pos {
		return endOfText, 0

	}
	r, w, err := i.r.ReadRune()
	if err != nil {
		i.atEOT = true
		return endOfText, 0
	}
	i.pos += w
	return r, w
}

func (i *inputReader) canCheckPrefix() bool {
	return false
}

func (i *inputReader) hasPrefix(re *Regexp) bool {
	return false
}

func (i *inputReader) index(re *Regexp, pos int) int {
	return -1
}

func (i *inputReader) context(pos int) lazyFlag {
	return 0 // not used
}

LiteralPrefix returns a literal string that must begin any match of the regular expression re. It returns the boolean true if the literal string comprises the entire regular expression.

func (re *Regexp) LiteralPrefix() (prefix string, complete bool) {
	return re.prefix, re.prefixComplete
}

MatchReader reports whether the text returned by the RuneReader contains any match of the regular expression re.

func (re *Regexp) MatchReader(r io.RuneReader) bool {
	return re.doMatch(r, nil, "")
}

MatchString reports whether the string s contains any match of the regular expression re.

func (re *Regexp) MatchString(s string) bool {
	return re.doMatch(nil, nil, s)
}

Match reports whether the byte slice b contains any match of the regular expression re.

func (re *Regexp) Match(b []byte) bool {
	return re.doMatch(nil, b, "")
}

MatchReader reports whether the text returned by the RuneReader contains any match of the regular expression pattern. More complicated queries need to use Compile and the full Regexp interface.

func MatchReader(pattern string, r io.RuneReader) (matched bool, err error) {
	re, err := Compile(pattern)
	if err != nil {
		return false, err
	}
	return re.MatchReader(r), nil
}

MatchString reports whether the string s contains any match of the regular expression pattern. More complicated queries need to use Compile and the full Regexp interface.

func MatchString(pattern string, s string) (matched bool, err error) {
	re, err := Compile(pattern)
	if err != nil {
		return false, err
	}
	return re.MatchString(s), nil
}

Match reports whether the byte slice b contains any match of the regular expression pattern. More complicated queries need to use Compile and the full Regexp interface.

func Match(pattern string, b []byte) (matched bool, err error) {
	re, err := Compile(pattern)
	if err != nil {
		return false, err
	}
	return re.Match(b), nil
}

ReplaceAllString returns a copy of src, replacing matches of the Regexp with the replacement string repl. Inside repl, $ signs are interpreted as in Expand, so for instance $1 represents the text of the first submatch.

func (re *Regexp) ReplaceAllString(src, repl string) string {
	n := 2
	if strings.Contains(repl, "$") {
		n = 2 * (re.numSubexp + 1)
	}
	b := re.replaceAll(nil, src, n, func(dst []byte, match []int) []byte {
		return re.expand(dst, repl, nil, src, match)
	})
	return string(b)
}

ReplaceAllLiteralString returns a copy of src, replacing matches of the Regexp with the replacement string repl. The replacement repl is substituted directly, without using Expand.

func (re *Regexp) ReplaceAllLiteralString(src, repl string) string {
	return string(re.replaceAll(nil, src, 2, func(dst []byte, match []int) []byte {
		return append(dst, repl...)
	}))
}

ReplaceAllStringFunc returns a copy of src in which all matches of the Regexp have been replaced by the return value of function repl applied to the matched substring. The replacement returned by repl is substituted directly, without using Expand.

func (re *Regexp) ReplaceAllStringFunc(src string, repl func(string) string) string {
	b := re.replaceAll(nil, src, 2, func(dst []byte, match []int) []byte {
		return append(dst, repl(src[match[0]:match[1]])...)
	})
	return string(b)
}

func (re *Regexp) replaceAll(bsrc []byte, src string, nmatch int, repl func(dst []byte, m []int) []byte) []byte {
	lastMatchEnd := 0 // end position of the most recent match
	searchPos := 0    // position where we next look for a match
	var buf []byte
	var endPos int
	if bsrc != nil {
		endPos = len(bsrc)
	} else {
		endPos = len(src)
	}
	if nmatch > re.prog.NumCap {
		nmatch = re.prog.NumCap
	}

	var dstCap [2]int
	for searchPos <= endPos {
		a := re.doExecute(nil, bsrc, src, searchPos, nmatch, dstCap[:0])
		if len(a) == 0 {
			break // no more matches
		}

Copy the unmatched characters before this match.

		if bsrc != nil {
			buf = append(buf, bsrc[lastMatchEnd:a[0]]...)
		} else {
			buf = append(buf, src[lastMatchEnd:a[0]]...)
		}

Now insert a copy of the replacement string, but not for a match of the empty string immediately after another match. (Otherwise, we get double replacement for patterns that match both empty and nonempty strings.)

		if a[1] > lastMatchEnd || a[0] == 0 {
			buf = repl(buf, a)
		}
		lastMatchEnd = a[1]

Advance past this match; always advance at least one character.

		var width int
		if bsrc != nil {
			_, width = utf8.DecodeRune(bsrc[searchPos:])
		} else {
			_, width = utf8.DecodeRuneInString(src[searchPos:])
		}
		if searchPos+width > a[1] {
			searchPos += width

This clause is only needed at the end of the input string. In that case, DecodeRuneInString returns width=0.

			searchPos++
		} else {
			searchPos = a[1]
		}
	}

Copy the unmatched characters after the last match.

	if bsrc != nil {
		buf = append(buf, bsrc[lastMatchEnd:]...)
	} else {
		buf = append(buf, src[lastMatchEnd:]...)
	}

	return buf
}

ReplaceAll returns a copy of src, replacing matches of the Regexp with the replacement text repl. Inside repl, $ signs are interpreted as in Expand, so for instance $1 represents the text of the first submatch.

func (re *Regexp) ReplaceAll(src, repl []byte) []byte {
	n := 2
	if bytes.IndexByte(repl, '$') >= 0 {
		n = 2 * (re.numSubexp + 1)
	}
	srepl := ""
	b := re.replaceAll(src, "", n, func(dst []byte, match []int) []byte {
		if len(srepl) != len(repl) {
			srepl = string(repl)
		}
		return re.expand(dst, srepl, src, "", match)
	})
	return b
}

ReplaceAllLiteral returns a copy of src, replacing matches of the Regexp with the replacement bytes repl. The replacement repl is substituted directly, without using Expand.

func (re *Regexp) ReplaceAllLiteral(src, repl []byte) []byte {
	return re.replaceAll(src, "", 2, func(dst []byte, match []int) []byte {
		return append(dst, repl...)
	})
}

ReplaceAllFunc returns a copy of src in which all matches of the Regexp have been replaced by the return value of function repl applied to the matched byte slice. The replacement returned by repl is substituted directly, without using Expand.

func (re *Regexp) ReplaceAllFunc(src []byte, repl func([]byte) []byte) []byte {
	return re.replaceAll(src, "", 2, func(dst []byte, match []int) []byte {
		return append(dst, repl(src[match[0]:match[1]])...)
	})
}

Bitmap used by func special to check whether a character needs to be escaped.

var specialBytes [16]byte

special reports whether byte b needs to be escaped by QuoteMeta.

func special(b byte) bool {
	return b < utf8.RuneSelf && specialBytes[b%16]&(1<<(b/16)) != 0
}

func init() {
	for _, b := range []byte(`\.+*?()|[]{}^$`) {
		specialBytes[b%16] |= 1 << (b / 16)
	}
}

QuoteMeta returns a string that escapes all regular expression metacharacters inside the argument text; the returned string is a regular expression matching the literal text.

A byte loop is correct because all metacharacters are ASCII.

	var i int
	for i = 0; i < len(s); i++ {
		if special(s[i]) {
			break
		}

No meta characters found, so return original string.

	if i >= len(s) {
		return s
	}

	b := make([]byte, 2*len(s)-i)
	copy(b, s[:i])
	j := i
	for ; i < len(s); i++ {
		if special(s[i]) {
			b[j] = '\\'
			j++
		}
		b[j] = s[i]
		j++
	}
	return string(b[:j])
}

The number of capture values in the program may correspond to fewer capturing expressions than are in the regexp. For example, "(a){0}" turns into an empty program, so the maximum capture in the program is 0 but we need to return an expression for \1. Pad appends -1s to the slice a as needed.

func (re *Regexp) pad(a []int) []int {

No match.

		return nil
	}
	n := (1 + re.numSubexp) * 2
	for len(a) < n {
		a = append(a, -1)
	}
	return a
}

allMatches calls deliver at most n times with the location of successive matches in the input text. The input text is b if non-nil, otherwise s.

func (re *Regexp) allMatches(s string, b []byte, n int, deliver func([]int)) {
	var end int
	if b == nil {
		end = len(s)
	} else {
		end = len(b)
	}

	for pos, i, prevMatchEnd := 0, 0, -1; i < n && pos <= end; {
		matches := re.doExecute(nil, b, s, pos, re.prog.NumCap, nil)
		if len(matches) == 0 {
			break
		}

		accept := true

We've found an empty match.

We don't allow an empty match right after a previous match, so ignore it.

				accept = false
			}

TODO: use step()

			if b == nil {
				_, width = utf8.DecodeRuneInString(s[pos:end])
			} else {
				_, width = utf8.DecodeRune(b[pos:end])
			}
			if width > 0 {
				pos += width
			} else {
				pos = end + 1
			}
		} else {
			pos = matches[1]
		}
		prevMatchEnd = matches[1]

		if accept {
			deliver(re.pad(matches))
			i++
		}
	}
}

Find returns a slice holding the text of the leftmost match in b of the regular expression. A return value of nil indicates no match.

func (re *Regexp) Find(b []byte) []byte {
	var dstCap [2]int
	a := re.doExecute(nil, b, "", 0, 2, dstCap[:0])
	if a == nil {
		return nil
	}
	return b[a[0]:a[1]:a[1]]
}

FindIndex returns a two-element slice of integers defining the location of the leftmost match in b of the regular expression. The match itself is at b[loc[0]:loc[1]]. A return value of nil indicates no match.

func (re *Regexp) FindIndex(b []byte) (loc []int) {
	a := re.doExecute(nil, b, "", 0, 2, nil)
	if a == nil {
		return nil
	}
	return a[0:2]
}

FindString returns a string holding the text of the leftmost match in s of the regular expression. If there is no match, the return value is an empty string, but it will also be empty if the regular expression successfully matches an empty string. Use FindStringIndex or FindStringSubmatch if it is necessary to distinguish these cases.

func (re *Regexp) FindString(s string) string {
	var dstCap [2]int
	a := re.doExecute(nil, nil, s, 0, 2, dstCap[:0])
	if a == nil {
		return ""
	}
	return s[a[0]:a[1]]
}

FindStringIndex returns a two-element slice of integers defining the location of the leftmost match in s of the regular expression. The match itself is at s[loc[0]:loc[1]]. A return value of nil indicates no match.

func (re *Regexp) FindStringIndex(s string) (loc []int) {
	a := re.doExecute(nil, nil, s, 0, 2, nil)
	if a == nil {
		return nil
	}
	return a[0:2]
}

FindReaderIndex returns a two-element slice of integers defining the location of the leftmost match of the regular expression in text read from the RuneReader. The match text was found in the input stream at byte offset loc[0] through loc[1]-1. A return value of nil indicates no match.

func (re *Regexp) FindReaderIndex(r io.RuneReader) (loc []int) {
	a := re.doExecute(r, nil, "", 0, 2, nil)
	if a == nil {
		return nil
	}
	return a[0:2]
}

FindSubmatch returns a slice of slices holding the text of the leftmost match of the regular expression in b and the matches, if any, of its subexpressions, as defined by the 'Submatch' descriptions in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindSubmatch(b []byte) [][]byte {
	var dstCap [4]int
	a := re.doExecute(nil, b, "", 0, re.prog.NumCap, dstCap[:0])
	if a == nil {
		return nil
	}
	ret := make([][]byte, 1+re.numSubexp)
	for i := range ret {
		if 2*i < len(a) && a[2*i] >= 0 {
			ret[i] = b[a[2*i]:a[2*i+1]:a[2*i+1]]
		}
	}
	return ret
}

Expand appends template to dst and returns the result; during the append, Expand replaces variables in the template with corresponding matches drawn from src. The match slice should have been returned by FindSubmatchIndex. In the template, a variable is denoted by a substring of the form $name or ${name}, where name is a non-empty sequence of letters, digits, and underscores. A purely numeric name like $1 refers to the submatch with the corresponding index; other names refer to capturing parentheses named with the (?P<name>...) syntax. A reference to an out of range or unmatched index or a name that is not present in the regular expression is replaced with an empty slice. In the $name form, name is taken to be as long as possible: $1x is equivalent to ${1x}, not ${1}x, and, $10 is equivalent to ${10}, not ${1}0. To insert a literal $ in the output, use $$ in the template.

func (re *Regexp) Expand(dst []byte, template []byte, src []byte, match []int) []byte {
	return re.expand(dst, string(template), src, "", match)
}

ExpandString is like Expand but the template and source are strings. It appends to and returns a byte slice in order to give the calling code control over allocation.

func (re *Regexp) ExpandString(dst []byte, template string, src string, match []int) []byte {
	return re.expand(dst, template, nil, src, match)
}

func (re *Regexp) expand(dst []byte, template string, bsrc []byte, src string, match []int) []byte {
	for len(template) > 0 {
		i := strings.Index(template, "$")
		if i < 0 {
			break
		}
		dst = append(dst, template[:i]...)
		template = template[i:]

Treat $$ as $.

			dst = append(dst, '$')
			template = template[2:]
			continue
		}
		name, num, rest, ok := extract(template)

Malformed; treat $ as raw text.

			dst = append(dst, '$')
			template = template[1:]
			continue
		}
		template = rest
		if num >= 0 {
			if 2*num+1 < len(match) && match[2*num] >= 0 {
				if bsrc != nil {
					dst = append(dst, bsrc[match[2*num]:match[2*num+1]]...)
				} else {
					dst = append(dst, src[match[2*num]:match[2*num+1]]...)
				}
			}
		} else {
			for i, namei := range re.subexpNames {
				if name == namei && 2*i+1 < len(match) && match[2*i] >= 0 {
					if bsrc != nil {
						dst = append(dst, bsrc[match[2*i]:match[2*i+1]]...)
					} else {
						dst = append(dst, src[match[2*i]:match[2*i+1]]...)
					}
					break
				}
			}
		}
	}
	dst = append(dst, template...)
	return dst
}

extract returns the name from a leading "$name" or "${name}" in str. If it is a number, extract returns num set to that number; otherwise num = -1.

func extract(str string) (name string, num int, rest string, ok bool) {
	if len(str) < 2 || str[0] != '$' {
		return
	}
	brace := false
	if str[1] == '{' {
		brace = true
		str = str[2:]
	} else {
		str = str[1:]
	}
	i := 0
	for i < len(str) {
		rune, size := utf8.DecodeRuneInString(str[i:])
		if !unicode.IsLetter(rune) && !unicode.IsDigit(rune) && rune != '_' {
			break
		}
		i += size
	}

empty name is not okay

		return
	}
	name = str[:i]
	if brace {

missing closing brace

			return
		}
		i++
	}

Parse number.

	num = 0
	for i := 0; i < len(name); i++ {
		if name[i] < '0' || '9' < name[i] || num >= 1e8 {
			num = -1
			break
		}
		num = num*10 + int(name[i]) - '0'

Disallow leading zeros.

	if name[0] == '0' && len(name) > 1 {
		num = -1
	}

	rest = str[i:]
	ok = true
	return
}

FindSubmatchIndex returns a slice holding the index pairs identifying the leftmost match of the regular expression in b and the matches, if any, of its subexpressions, as defined by the 'Submatch' and 'Index' descriptions in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindSubmatchIndex(b []byte) []int {
	return re.pad(re.doExecute(nil, b, "", 0, re.prog.NumCap, nil))
}

FindStringSubmatch returns a slice of strings holding the text of the leftmost match of the regular expression in s and the matches, if any, of its subexpressions, as defined by the 'Submatch' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindStringSubmatch(s string) []string {
	var dstCap [4]int
	a := re.doExecute(nil, nil, s, 0, re.prog.NumCap, dstCap[:0])
	if a == nil {
		return nil
	}
	ret := make([]string, 1+re.numSubexp)
	for i := range ret {
		if 2*i < len(a) && a[2*i] >= 0 {
			ret[i] = s[a[2*i]:a[2*i+1]]
		}
	}
	return ret
}

FindStringSubmatchIndex returns a slice holding the index pairs identifying the leftmost match of the regular expression in s and the matches, if any, of its subexpressions, as defined by the 'Submatch' and 'Index' descriptions in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindStringSubmatchIndex(s string) []int {
	return re.pad(re.doExecute(nil, nil, s, 0, re.prog.NumCap, nil))
}

FindReaderSubmatchIndex returns a slice holding the index pairs identifying the leftmost match of the regular expression of text read by the RuneReader, and the matches, if any, of its subexpressions, as defined by the 'Submatch' and 'Index' descriptions in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindReaderSubmatchIndex(r io.RuneReader) []int {
	return re.pad(re.doExecute(r, nil, "", 0, re.prog.NumCap, nil))
}

const startSize = 10 // The size at which to start a slice in the 'All' routines.

FindAll is the 'All' version of Find; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAll(b []byte, n int) [][]byte {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][]byte
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][]byte, 0, startSize)
		}
		result = append(result, b[match[0]:match[1]:match[1]])
	})
	return result
}

FindAllIndex is the 'All' version of FindIndex; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAllIndex(b []byte, n int) [][]int {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][]int
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match[0:2])
	})
	return result
}

FindAllString is the 'All' version of FindString; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAllString(s string, n int) []string {
	if n < 0 {
		n = len(s) + 1
	}
	var result []string
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([]string, 0, startSize)
		}
		result = append(result, s[match[0]:match[1]])
	})
	return result
}

FindAllStringIndex is the 'All' version of FindStringIndex; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAllStringIndex(s string, n int) [][]int {
	if n < 0 {
		n = len(s) + 1
	}
	var result [][]int
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match[0:2])
	})
	return result
}

FindAllSubmatch is the 'All' version of FindSubmatch; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAllSubmatch(b []byte, n int) [][][]byte {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][][]byte
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][][]byte, 0, startSize)
		}
		slice := make([][]byte, len(match)/2)
		for j := range slice {
			if match[2*j] >= 0 {
				slice[j] = b[match[2*j]:match[2*j+1]:match[2*j+1]]
			}
		}
		result = append(result, slice)
	})
	return result
}

FindAllSubmatchIndex is the 'All' version of FindSubmatchIndex; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAllSubmatchIndex(b []byte, n int) [][]int {
	if n < 0 {
		n = len(b) + 1
	}
	var result [][]int
	re.allMatches("", b, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match)
	})
	return result
}

FindAllStringSubmatch is the 'All' version of FindStringSubmatch; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAllStringSubmatch(s string, n int) [][]string {
	if n < 0 {
		n = len(s) + 1
	}
	var result [][]string
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([][]string, 0, startSize)
		}
		slice := make([]string, len(match)/2)
		for j := range slice {
			if match[2*j] >= 0 {
				slice[j] = s[match[2*j]:match[2*j+1]]
			}
		}
		result = append(result, slice)
	})
	return result
}

FindAllStringSubmatchIndex is the 'All' version of FindStringSubmatchIndex; it returns a slice of all successive matches of the expression, as defined by the 'All' description in the package comment. A return value of nil indicates no match.

func (re *Regexp) FindAllStringSubmatchIndex(s string, n int) [][]int {
	if n < 0 {
		n = len(s) + 1
	}
	var result [][]int
	re.allMatches(s, nil, n, func(match []int) {
		if result == nil {
			result = make([][]int, 0, startSize)
		}
		result = append(result, match)
	})
	return result
}

Split slices s into substrings separated by the expression and returns a slice of the substrings between those expression matches. The slice returned by this method consists of all the substrings of s not contained in the slice returned by FindAllString. When called on an expression that contains no metacharacters, it is equivalent to strings.SplitN. Example: s := regexp.MustCompile("a*").Split("abaabaccadaaae", 5) // s: ["", "b", "b", "c", "cadaaae"] The count determines the number of substrings to return: n > 0: at most n substrings; the last substring will be the unsplit remainder. n == 0: the result is nil (zero substrings) n < 0: all substrings

func (re *Regexp) Split(s string, n int) []string {

	if n == 0 {
		return nil
	}

	if len(re.expr) > 0 && len(s) == 0 {
		return []string{""}
	}

	matches := re.FindAllStringIndex(s, n)
	strings := make([]string, 0, len(matches))

	beg := 0
	end := 0
	for _, match := range matches {
		if n > 0 && len(strings) >= n-1 {
			break
		}

		end = match[0]
		if match[1] != 0 {
			strings = append(strings, s[beg:end])
		}
		beg = match[1]
	}

	if end != len(s) {
		strings = append(strings, s[beg:])
	}

	return strings