Newer
Older
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// 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
// 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.)
"regexp/syntax"
"strconv"
// 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.
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
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 {
// 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.
// 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()
re = re.Simplify()
prog, err := syntax.Compile(re)
if err != nil {
return nil, err
}
matchcap := prog.NumCap
if matchcap < 2 {
matchcap = 2
}
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)
regexp.prefix, regexp.prefixComplete, regexp.prefixEnd = onePassPrefix(prog)
if regexp.prefix != "" {
// 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)
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
// 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())
// 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())
func quote(s string) string {
if strconv.CanBackquote(s) {
return "`" + 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
}
// 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
}
// inputString scans a string.
type inputString struct {
str string
}
if pos < len(i.str) {
}
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:])
}
// inputBytes scans a byte slice.
type inputBytes struct {
str []byte
}
if pos < len(i.str) {
}
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:])
}
// inputReader scans a RuneReader.
type inputReader struct {
r io.RuneReader
atEOT bool
pos 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, "")
Rob Pike
committed
// 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
}
Rob Pike
committed
// 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)
Rob Pike
committed
if err != nil {
return false, err
Rob Pike
committed
}
Rob Pike
committed
}
// 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 $1 represents the text of the first submatch.
func (re *Regexp) ReplaceAllString(src, repl string) string {
if strings.Contains(repl, "$") {
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])
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 {
// 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
} else if searchPos+1 > a[1] {
// This clause is only needed at the end of the input
// string. In that case, DecodeRuneInString returns width=0.
searchPos++
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:]...)
}
// 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
func QuoteMeta(s string) string {
// 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++ {
// 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 {
if a == nil {
// 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)) {
end = len(s)
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 {
if matches[1] == pos {
// We've found an empty match.
if matches[0] == prevMatchEnd {
// We don't allow an empty match right
// after a previous match, so ignore it.
accept = false
// TODO: use step()
_, width = utf8.DecodeRuneInString(s[pos:end])
_, width = utf8.DecodeRune(b[pos:end])
}
if width > 0 {
pos += width
pos = matches[1]
prevMatchEnd = matches[1]
}
}
}
// 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)
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
// 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 $$ in the template.
func (re *Regexp) Expand(dst []byte, template []byte, src []byte, match []int) []byte {
return re.expand(dst, string(template), src, "", match)
}
// ExpandString is like Expand but the template and source are strings.
// It appends to and returns a byte slice in order to give the calling
func (re *Regexp) ExpandString(dst []byte, template string, src string, match []int) []byte {
return re.expand(dst, template, nil, src, match)
}
func (re *Regexp) expand(dst []byte, template string, bsrc []byte, src string, match []int) []byte {
for len(template) > 0 {
before, after, ok := strings.Cut(template, "$")
if !ok {
dst = append(dst, before...)
template = after
if template != "" && template[0] == '$' {
// Treat $$ as $.
dst = append(dst, '$')
continue
}
name, num, rest, ok := extract(template)
if !ok {
// Malformed; treat $ as raw text.
dst = append(dst, '$')
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.
// (The $ has already been removed by the caller.)
// 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) {
return
}
brace := false
brace = true
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
}
if i == 0 {
// empty name is not okay
return
}
name = str[:i]
if brace {
if i >= len(str) || str[i] != '}' {
// missing closing brace
return
}
i++
}