package strings
Import Path
strings (on go.dev)
Dependency Relation
imports 9 packages, and imported by 92 packages
Involved Source Files
builder.go
clone.go
compare.go
reader.go
replace.go
search.go
Package strings implements simple functions to manipulate UTF-8 encoded strings.
For information about UTF-8 strings in Go, see https://blog.golang.org/strings.
Code Examples
package main
import (
"fmt"
"strings"
)
func main() {
var b strings.Builder
for i := 3; i >= 1; i-- {
fmt.Fprintf(&b, "%d...", i)
}
b.WriteString("ignition")
fmt.Println(b.String())
}
package main
import (
"fmt"
"strings"
"unsafe"
)
func main() {
s := "abc"
clone := strings.Clone(s)
fmt.Println(s == clone)
fmt.Println(unsafe.StringData(s) == unsafe.StringData(clone))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.Compare("a", "b"))
fmt.Println(strings.Compare("a", "a"))
fmt.Println(strings.Compare("b", "a"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.Contains("seafood", "foo"))
fmt.Println(strings.Contains("seafood", "bar"))
fmt.Println(strings.Contains("seafood", ""))
fmt.Println(strings.Contains("", ""))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.ContainsAny("team", "i"))
fmt.Println(strings.ContainsAny("fail", "ui"))
fmt.Println(strings.ContainsAny("ure", "ui"))
fmt.Println(strings.ContainsAny("failure", "ui"))
fmt.Println(strings.ContainsAny("foo", ""))
fmt.Println(strings.ContainsAny("", ""))
}
package main
import (
"fmt"
"strings"
)
func main() {
f := func(r rune) bool {
return r == 'a' || r == 'e' || r == 'i' || r == 'o' || r == 'u'
}
fmt.Println(strings.ContainsFunc("hello", f))
fmt.Println(strings.ContainsFunc("rhythms", f))
}
package main
import (
"fmt"
"strings"
)
func main() {
// Finds whether a string contains a particular Unicode code point.
// The code point for the lowercase letter "a", for example, is 97.
fmt.Println(strings.ContainsRune("aardvark", 97))
fmt.Println(strings.ContainsRune("timeout", 97))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.Count("cheese", "e"))
fmt.Println(strings.Count("five", "")) // before & after each rune
}
package main
import (
"fmt"
"strings"
)
func main() {
show := func(s, sep string) {
before, after, found := strings.Cut(s, sep)
fmt.Printf("Cut(%q, %q) = %q, %q, %v\n", s, sep, before, after, found)
}
show("Gopher", "Go")
show("Gopher", "ph")
show("Gopher", "er")
show("Gopher", "Badger")
}
package main
import (
"fmt"
"strings"
)
func main() {
show := func(s, sep string) {
after, found := strings.CutPrefix(s, sep)
fmt.Printf("CutPrefix(%q, %q) = %q, %v\n", s, sep, after, found)
}
show("Gopher", "Go")
show("Gopher", "ph")
}
package main
import (
"fmt"
"strings"
)
func main() {
show := func(s, sep string) {
before, found := strings.CutSuffix(s, sep)
fmt.Printf("CutSuffix(%q, %q) = %q, %v\n", s, sep, before, found)
}
show("Gopher", "Go")
show("Gopher", "er")
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.EqualFold("Go", "go"))
fmt.Println(strings.EqualFold("AB", "ab")) // true because comparison uses simple case-folding
fmt.Println(strings.EqualFold("ß", "ss")) // false because comparison does not use full case-folding
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Printf("Fields are: %q", strings.Fields(" foo bar baz "))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
f := func(c rune) bool {
return !unicode.IsLetter(c) && !unicode.IsNumber(c)
}
fmt.Printf("Fields are: %q", strings.FieldsFunc(" foo1;bar2,baz3...", f))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.HasPrefix("Gopher", "Go"))
fmt.Println(strings.HasPrefix("Gopher", "C"))
fmt.Println(strings.HasPrefix("Gopher", ""))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.HasSuffix("Amigo", "go"))
fmt.Println(strings.HasSuffix("Amigo", "O"))
fmt.Println(strings.HasSuffix("Amigo", "Ami"))
fmt.Println(strings.HasSuffix("Amigo", ""))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.Index("chicken", "ken"))
fmt.Println(strings.Index("chicken", "dmr"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.IndexAny("chicken", "aeiouy"))
fmt.Println(strings.IndexAny("crwth", "aeiouy"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.IndexByte("golang", 'g'))
fmt.Println(strings.IndexByte("gophers", 'h'))
fmt.Println(strings.IndexByte("golang", 'x'))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
f := func(c rune) bool {
return unicode.Is(unicode.Han, c)
}
fmt.Println(strings.IndexFunc("Hello, 世界", f))
fmt.Println(strings.IndexFunc("Hello, world", f))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.IndexRune("chicken", 'k'))
fmt.Println(strings.IndexRune("chicken", 'd'))
}
package main
import (
"fmt"
"strings"
)
func main() {
s := []string{"foo", "bar", "baz"}
fmt.Println(strings.Join(s, ", "))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.Index("go gopher", "go"))
fmt.Println(strings.LastIndex("go gopher", "go"))
fmt.Println(strings.LastIndex("go gopher", "rodent"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.LastIndexAny("go gopher", "go"))
fmt.Println(strings.LastIndexAny("go gopher", "rodent"))
fmt.Println(strings.LastIndexAny("go gopher", "fail"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.LastIndexByte("Hello, world", 'l'))
fmt.Println(strings.LastIndexByte("Hello, world", 'o'))
fmt.Println(strings.LastIndexByte("Hello, world", 'x'))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
fmt.Println(strings.LastIndexFunc("go 123", unicode.IsNumber))
fmt.Println(strings.LastIndexFunc("123 go", unicode.IsNumber))
fmt.Println(strings.LastIndexFunc("go", unicode.IsNumber))
}
package main
import (
"fmt"
"strings"
)
func main() {
rot13 := func(r rune) rune {
switch {
case r >= 'A' && r <= 'Z':
return 'A' + (r-'A'+13)%26
case r >= 'a' && r <= 'z':
return 'a' + (r-'a'+13)%26
}
return r
}
fmt.Println(strings.Map(rot13, "'Twas brillig and the slithy gopher..."))
}
package main
import (
"fmt"
"strings"
)
func main() {
r := strings.NewReplacer("<", "<", ">", ">")
fmt.Println(r.Replace("This is <b>HTML</b>!"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println("ba" + strings.Repeat("na", 2))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.Replace("oink oink oink", "k", "ky", 2))
fmt.Println(strings.Replace("oink oink oink", "oink", "moo", -1))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.ReplaceAll("oink oink oink", "oink", "moo"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Printf("%q\n", strings.Split("a,b,c", ","))
fmt.Printf("%q\n", strings.Split("a man a plan a canal panama", "a "))
fmt.Printf("%q\n", strings.Split(" xyz ", ""))
fmt.Printf("%q\n", strings.Split("", "Bernardo O'Higgins"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Printf("%q\n", strings.SplitAfter("a,b,c", ","))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Printf("%q\n", strings.SplitAfterN("a,b,c", ",", 2))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Printf("%q\n", strings.SplitN("a,b,c", ",", 2))
z := strings.SplitN("a,b,c", ",", 0)
fmt.Printf("%q (nil = %v)\n", z, z == nil)
}
package main
import (
"fmt"
"strings"
)
func main() {
// Compare this example to the ToTitle example.
fmt.Println(strings.Title("her royal highness"))
fmt.Println(strings.Title("loud noises"))
fmt.Println(strings.Title("хлеб"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.ToLower("Gopher"))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
fmt.Println(strings.ToLowerSpecial(unicode.TurkishCase, "Önnek İş"))
}
package main
import (
"fmt"
"strings"
)
func main() {
// Compare this example to the Title example.
fmt.Println(strings.ToTitle("her royal highness"))
fmt.Println(strings.ToTitle("loud noises"))
fmt.Println(strings.ToTitle("хлеб"))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
fmt.Println(strings.ToTitleSpecial(unicode.TurkishCase, "dünyanın ilk borsa yapısı Aizonai kabul edilir"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.ToUpper("Gopher"))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
fmt.Println(strings.ToUpperSpecial(unicode.TurkishCase, "örnek iş"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Printf("%s\n", strings.ToValidUTF8("abc", "\uFFFD"))
fmt.Printf("%s\n", strings.ToValidUTF8("a\xffb\xC0\xAFc\xff", ""))
fmt.Printf("%s\n", strings.ToValidUTF8("\xed\xa0\x80", "abc"))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Print(strings.Trim("¡¡¡Hello, Gophers!!!", "!¡"))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
fmt.Print(strings.TrimFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Print(strings.TrimLeft("¡¡¡Hello, Gophers!!!", "!¡"))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
fmt.Print(strings.TrimLeftFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))
}
package main
import (
"fmt"
"strings"
)
func main() {
var s = "¡¡¡Hello, Gophers!!!"
s = strings.TrimPrefix(s, "¡¡¡Hello, ")
s = strings.TrimPrefix(s, "¡¡¡Howdy, ")
fmt.Print(s)
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Print(strings.TrimRight("¡¡¡Hello, Gophers!!!", "!¡"))
}
package main
import (
"fmt"
"strings"
"unicode"
)
func main() {
fmt.Print(strings.TrimRightFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))
}
package main
import (
"fmt"
"strings"
)
func main() {
fmt.Println(strings.TrimSpace(" \t\n Hello, Gophers \n\t\r\n"))
}
package main
import (
"fmt"
"strings"
)
func main() {
var s = "¡¡¡Hello, Gophers!!!"
s = strings.TrimSuffix(s, ", Gophers!!!")
s = strings.TrimSuffix(s, ", Marmots!!!")
fmt.Print(s)
}
Package-Level Type Names (total 3)
A Builder is used to efficiently build a string using [Builder.Write] methods.
It minimizes memory copying. The zero value is ready to use.
Do not copy a non-zero Builder.
Cap returns the capacity of the builder's underlying byte slice. It is the
total space allocated for the string being built and includes any bytes
already written.
Grow grows b's capacity, if necessary, to guarantee space for
another n bytes. After Grow(n), at least n bytes can be written to b
without another allocation. If n is negative, Grow panics.
Len returns the number of accumulated bytes; b.Len() == len(b.String()).
Reset resets the [Builder] to be empty.
String returns the accumulated string.
Write appends the contents of p to b's buffer.
Write always returns len(p), nil.
WriteByte appends the byte c to b's buffer.
The returned error is always nil.
WriteRune appends the UTF-8 encoding of Unicode code point r to b's buffer.
It returns the length of r and a nil error.
WriteString appends the contents of s to b's buffer.
It returns the length of s and a nil error.
*Builder : expvar.Var
*Builder : fmt.Stringer
*Builder : internal/bisect.Writer
*Builder : io.ByteWriter
*Builder : io.StringWriter
*Builder : io.Writer
A Reader implements the [io.Reader], [io.ReaderAt], [io.ByteReader], [io.ByteScanner],
[io.RuneReader], [io.RuneScanner], [io.Seeker], and [io.WriterTo] interfaces by reading
from a string.
The zero value for Reader operates like a Reader of an empty string.
Len returns the number of bytes of the unread portion of the
string.
Read implements the [io.Reader] interface.
ReadAt implements the [io.ReaderAt] interface.
ReadByte implements the [io.ByteReader] interface.
ReadRune implements the [io.RuneReader] interface.
Reset resets the [Reader] to be reading from s.
Seek implements the [io.Seeker] interface.
Size returns the original length of the underlying string.
Size is the number of bytes available for reading via [Reader.ReadAt].
The returned value is always the same and is not affected by calls
to any other method.
UnreadByte implements the [io.ByteScanner] interface.
UnreadRune implements the [io.RuneScanner] interface.
WriteTo implements the [io.WriterTo] interface.
*Reader : compress/flate.Reader
*Reader : image/jpeg.Reader
*Reader : io.ByteReader
*Reader : io.ByteScanner
*Reader : io.Reader
*Reader : io.ReaderAt
*Reader : io.ReadSeeker
*Reader : io.RuneReader
*Reader : io.RuneScanner
*Reader : io.Seeker
*Reader : io.WriterTo
func NewReader(s string) *Reader
Replacer replaces a list of strings with replacements.
It is safe for concurrent use by multiple goroutines.
Replace returns a copy of s with all replacements performed.
WriteString writes s to w with all replacements performed.
func NewReplacer(oldnew ...string) *Replacer
Package-Level Functions (total 52)
Clone returns a fresh copy of s.
It guarantees to make a copy of s into a new allocation,
which can be important when retaining only a small substring
of a much larger string. Using Clone can help such programs
use less memory. Of course, since using Clone makes a copy,
overuse of Clone can make programs use more memory.
Clone should typically be used only rarely, and only when
profiling indicates that it is needed.
For strings of length zero the string "" will be returned
and no allocation is made.
Compare returns an integer comparing two strings lexicographically.
The result will be 0 if a == b, -1 if a < b, and +1 if a > b.
Use Compare when you need to perform a three-way comparison (with
[slices.SortFunc], for example). It is usually clearer and always faster
to use the built-in string comparison operators ==, <, >, and so on.
Contains reports whether substr is within s.
ContainsAny reports whether any Unicode code points in chars are within s.
ContainsFunc reports whether any Unicode code points r within s satisfy f(r).
ContainsRune reports whether the Unicode code point r is within s.
Count counts the number of non-overlapping instances of substr in s.
If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
Cut slices s around the first instance of sep,
returning the text before and after sep.
The found result reports whether sep appears in s.
If sep does not appear in s, cut returns s, "", false.
CutPrefix returns s without the provided leading prefix string
and reports whether it found the prefix.
If s doesn't start with prefix, CutPrefix returns s, false.
If prefix is the empty string, CutPrefix returns s, true.
CutSuffix returns s without the provided ending suffix string
and reports whether it found the suffix.
If s doesn't end with suffix, CutSuffix returns s, false.
If suffix is the empty string, CutSuffix returns s, true.
EqualFold reports whether s and t, interpreted as UTF-8 strings,
are equal under simple Unicode case-folding, which is a more general
form of case-insensitivity.
Fields splits the string s around each instance of one or more consecutive white space
characters, as defined by [unicode.IsSpace], returning a slice of substrings of s or an
empty slice if s contains only white space.
FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
and returns an array of slices of s. If all code points in s satisfy f(c) or the
string is empty, an empty slice is returned.
FieldsFunc makes no guarantees about the order in which it calls f(c)
and assumes that f always returns the same value for a given c.
HasPrefix reports whether the string s begins with prefix.
HasSuffix reports whether the string s ends with suffix.
Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
IndexAny returns the index of the first instance of any Unicode code point
from chars in s, or -1 if no Unicode code point from chars is present in s.
IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.
IndexFunc returns the index into s of the first Unicode
code point satisfying f(c), or -1 if none do.
IndexRune returns the index of the first instance of the Unicode code point
r, or -1 if rune is not present in s.
If r is [utf8.RuneError], it returns the first instance of any
invalid UTF-8 byte sequence.
Join concatenates the elements of its first argument to create a single string. The separator
string sep is placed between elements in the resulting string.
LastIndex returns the index of the last instance of substr in s, or -1 if substr is not present in s.
LastIndexAny returns the index of the last instance of any Unicode code
point from chars in s, or -1 if no Unicode code point from chars is
present in s.
LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
LastIndexFunc returns the index into s of the last
Unicode code point satisfying f(c), or -1 if none do.
Map returns a copy of the string s with all its characters modified
according to the mapping function. If mapping returns a negative value, the character is
dropped from the string with no replacement.
NewReader returns a new [Reader] reading from s.
It is similar to [bytes.NewBufferString] but more efficient and non-writable.
NewReplacer returns a new [Replacer] from a list of old, new string
pairs. Replacements are performed in the order they appear in the
target string, without overlapping matches. The old string
comparisons are done in argument order.
NewReplacer panics if given an odd number of arguments.
Repeat returns a new string consisting of count copies of the string s.
It panics if count is negative or if the result of (len(s) * count)
overflows.
Replace returns a copy of the string s with the first n
non-overlapping instances of old replaced by new.
If old is empty, it matches at the beginning of the string
and after each UTF-8 sequence, yielding up to k+1 replacements
for a k-rune string.
If n < 0, there is no limit on the number of replacements.
ReplaceAll returns a copy of the string s with all
non-overlapping instances of old replaced by new.
If old is empty, it matches at the beginning of the string
and after each UTF-8 sequence, yielding up to k+1 replacements
for a k-rune string.
Split slices s into all substrings separated by sep and returns a slice of
the substrings between those separators.
If s does not contain sep and sep is not empty, Split returns a
slice of length 1 whose only element is s.
If sep is empty, Split splits after each UTF-8 sequence. If both s
and sep are empty, Split returns an empty slice.
It is equivalent to [SplitN] with a count of -1.
To split around the first instance of a separator, see [Cut].
SplitAfter slices s into all substrings after each instance of sep and
returns a slice of those substrings.
If s does not contain sep and sep is not empty, SplitAfter returns
a slice of length 1 whose only element is s.
If sep is empty, SplitAfter splits after each UTF-8 sequence. If
both s and sep are empty, SplitAfter returns an empty slice.
It is equivalent to [SplitAfterN] with a count of -1.
SplitAfterN slices s into substrings after each instance of sep and
returns a slice of those substrings.
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
Edge cases for s and sep (for example, empty strings) are handled
as described in the documentation for SplitAfter.
SplitN slices s into substrings separated by sep and returns a slice of
the substrings between those separators.
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
Edge cases for s and sep (for example, empty strings) are handled
as described in the documentation for [Split].
To split around the first instance of a separator, see [Cut].
Title returns a copy of the string s with all Unicode letters that begin words
mapped to their Unicode title case.
Deprecated: The rule Title uses for word boundaries does not handle Unicode
punctuation properly. Use golang.org/x/text/cases instead.
ToLower returns s with all Unicode letters mapped to their lower case.
ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
lower case using the case mapping specified by c.
ToTitle returns a copy of the string s with all Unicode letters mapped to
their Unicode title case.
ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
Unicode title case, giving priority to the special casing rules.
ToUpper returns s with all Unicode letters mapped to their upper case.
ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their
upper case using the case mapping specified by c.
ToValidUTF8 returns a copy of the string s with each run of invalid UTF-8 byte sequences
replaced by the replacement string, which may be empty.
Trim returns a slice of the string s with all leading and
trailing Unicode code points contained in cutset removed.
TrimFunc returns a slice of the string s with all leading
and trailing Unicode code points c satisfying f(c) removed.
TrimLeft returns a slice of the string s with all leading
Unicode code points contained in cutset removed.
To remove a prefix, use [TrimPrefix] instead.
TrimLeftFunc returns a slice of the string s with all leading
Unicode code points c satisfying f(c) removed.
TrimPrefix returns s without the provided leading prefix string.
If s doesn't start with prefix, s is returned unchanged.
TrimRight returns a slice of the string s, with all trailing
Unicode code points contained in cutset removed.
To remove a suffix, use [TrimSuffix] instead.
TrimRightFunc returns a slice of the string s with all trailing
Unicode code points c satisfying f(c) removed.
TrimSpace returns a slice of the string s, with all leading
and trailing white space removed, as defined by Unicode.
TrimSuffix returns s without the provided trailing suffix string.
If s doesn't end with suffix, s is returned unchanged.
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