Package strings

Compare is included only for symmetry with package bytes. It is usually clearer and always faster to use the built-in string comparison operators ==, <, >, and so on.

Example

Code:

fmt.Println(strings.Compare("a", "b"))
fmt.Println(strings.Compare("a", "a"))
fmt.Println(strings.Compare("b", "a"))

Output:

-1
0
1

func Contains

func Contains(s, substr string) bool

Contains reports whether substr is within s.

Example

Code:

fmt.Println(strings.Contains("seafood", "foo"))
fmt.Println(strings.Contains("seafood", "bar"))
fmt.Println(strings.Contains("seafood", ""))
fmt.Println(strings.Contains("", ""))

Output:

true
false
true
true

func ContainsAny

func ContainsAny(s, chars string) bool

ContainsAny reports whether any Unicode code points in chars are within s.

Example

Code:

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("", ""))

Output:

false
true
true
true
false
false

func ContainsRune

func ContainsRune(s string, r rune) bool

ContainsRune reports whether the Unicode code point r is within s.

Example

Code:

// 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))

Output:

true
false

func Count

func Count(s, substr string) int

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.

Example

Code:

fmt.Println(strings.Count("cheese", "e"))
fmt.Println(strings.Count("five", "")) // before & after each rune

Output:

3
5

func EqualFold

func EqualFold(s, t string) bool

EqualFold reports whether s and t, interpreted as UTF-8 strings, are equal under Unicode case-folding.

Example

Code:

fmt.Println(strings.EqualFold("Go", "go"))

Output:

true

func Fields

func Fields(s string) []string

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.

Example

Code:

fmt.Printf("Fields are: %q", strings.Fields("  foo bar  baz   "))

Output:

Fields are: ["foo" "bar" "baz"]

func FieldsFunc

func FieldsFunc(s string, f func(rune) bool) []string

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). If f does not return consistent results for a given c, FieldsFunc may crash.

Example

Code:

f := func(c rune) bool {
    return !unicode.IsLetter(c) && !unicode.IsNumber(c)
}
fmt.Printf("Fields are: %q", strings.FieldsFunc("  foo1;bar2,baz3...", f))

Output:

Fields are: ["foo1" "bar2" "baz3"]

func HasPrefix

func HasPrefix(s, prefix string) bool

HasPrefix tests whether the string s begins with prefix.

Example

Code:

fmt.Println(strings.HasPrefix("Gopher", "Go"))
fmt.Println(strings.HasPrefix("Gopher", "C"))
fmt.Println(strings.HasPrefix("Gopher", ""))

Output:

true
false
true

func HasSuffix

func HasSuffix(s, suffix string) bool

HasSuffix tests whether the string s ends with suffix.

Example

Code:

fmt.Println(strings.HasSuffix("Amigo", "go"))
fmt.Println(strings.HasSuffix("Amigo", "O"))
fmt.Println(strings.HasSuffix("Amigo", "Ami"))
fmt.Println(strings.HasSuffix("Amigo", ""))

Output:

true
false
false
true

func Index

func Index(s, substr string) int

Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.

Example

Code:

fmt.Println(strings.Index("chicken", "ken"))
fmt.Println(strings.Index("chicken", "dmr"))

Output:

4
-1

func IndexAny

func IndexAny(s, chars string) int

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.

Example

Code:

fmt.Println(strings.IndexAny("chicken", "aeiouy"))
fmt.Println(strings.IndexAny("crwth", "aeiouy"))

Output:

2
-1

func IndexByte

func IndexByte(s string, c byte) int

IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.

Example

Code:

fmt.Println(strings.IndexByte("golang", 'g'))
fmt.Println(strings.IndexByte("gophers", 'h'))
fmt.Println(strings.IndexByte("golang", 'x'))

Output:

0
3
-1

func IndexFunc

func IndexFunc(s string, f func(rune) bool) int

IndexFunc returns the index into s of the first Unicode code point satisfying f(c), or -1 if none do.

Example

Code:

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))

Output:

7
-1

func IndexRune

func IndexRune(s string, r rune) int

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.

Example

Code:

fmt.Println(strings.IndexRune("chicken", 'k'))
fmt.Println(strings.IndexRune("chicken", 'd'))

Output:

4
-1

func Join

func Join(a []string, sep string) string

Join concatenates the elements of a to create a single string. The separator string sep is placed between elements in the resulting string.

Example

Code:

s := []string{"foo", "bar", "baz"}
fmt.Println(strings.Join(s, ", "))

Output:

foo, bar, baz

func LastIndex

func LastIndex(s, substr string) int

LastIndex returns the index of the last instance of substr in s, or -1 if substr is not present in s.

Example

Code:

fmt.Println(strings.Index("go gopher", "go"))
fmt.Println(strings.LastIndex("go gopher", "go"))
fmt.Println(strings.LastIndex("go gopher", "rodent"))

Output:

0
3
-1

func LastIndexAny

func LastIndexAny(s, chars string) int

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.

Example

Code:

fmt.Println(strings.LastIndexAny("go gopher", "go"))
fmt.Println(strings.LastIndexAny("go gopher", "rodent"))
fmt.Println(strings.LastIndexAny("go gopher", "fail"))

Output:

4
8
-1

func LastIndexByte

func LastIndexByte(s string, c byte) int

LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.

Example

Code:

fmt.Println(strings.LastIndexByte("Hello, world", 'l'))
fmt.Println(strings.LastIndexByte("Hello, world", 'o'))
fmt.Println(strings.LastIndexByte("Hello, world", 'x'))

Output:

10
8
-1

func LastIndexFunc

func LastIndexFunc(s string, f func(rune) bool) int

LastIndexFunc returns the index into s of the last Unicode code point satisfying f(c), or -1 if none do.

Example

Code:

fmt.Println(strings.LastIndexFunc("go 123", unicode.IsNumber))
fmt.Println(strings.LastIndexFunc("123 go", unicode.IsNumber))
fmt.Println(strings.LastIndexFunc("go", unicode.IsNumber))

Output:

5
2
-1

func Map

func Map(mapping func(rune) rune, s string) string

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.

Example

Code:

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..."))

Output:

'Gjnf oevyyvt naq gur fyvgul tbcure...

func Repeat

func Repeat(s string, count int) string

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.

Example

Code:

fmt.Println("ba" + strings.Repeat("na", 2))

Output:

banana

func Replace

func Replace(s, old, new string, n int) string

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.

Example

Code:

fmt.Println(strings.Replace("oink oink oink", "k", "ky", 2))
fmt.Println(strings.Replace("oink oink oink", "oink", "moo", -1))

Output:

oinky oinky oink
moo moo moo

func ReplaceAll

func ReplaceAll(s, old, new string) string

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.

Example

Code:

fmt.Println(strings.ReplaceAll("oink oink oink", "oink", "moo"))

Output:

moo moo moo

func Split

func Split(s, sep string) []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.

Example

Code:

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"))

Output:

["a" "b" "c"]
["" "man " "plan " "canal panama"]
[" " "x" "y" "z" " "]
[""]

func SplitAfter

func SplitAfter(s, sep string) []string

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.

Example

Code:

fmt.Printf("%q\n", strings.SplitAfter("a,b,c", ","))

Output:

["a," "b," "c"]

func SplitAfterN

func SplitAfterN(s, sep string, n int) []string

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.

Example

Code:

fmt.Printf("%q\n", strings.SplitAfterN("a,b,c", ",", 2))

Output:

["a," "b,c"]

func SplitN

func SplitN(s, sep string, n int) []string

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.

Example

Code:

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)

Output:

["a" "b,c"]
[] (nil = true)

func Title

func Title(s string) string

Title returns a copy of the string s with all Unicode letters that begin words mapped to their Unicode title case.

BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.

Example

Code:

// 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"))

Output:

Her Royal Highness
Loud Noises
Хлеб

func ToLower

func ToLower(s string) string

ToLower returns s with all Unicode letters mapped to their lower case.

Example

Code:

fmt.Println(strings.ToLower("Gopher"))

Output:

gopher

func ToLowerSpecial

func ToLowerSpecial(c unicode.SpecialCase, s string) string

ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their lower case using the case mapping specified by c.

Example

Code:

fmt.Println(strings.ToLowerSpecial(unicode.TurkishCase, "Önnek İş"))

Output:

önnek iş

func ToTitle

func ToTitle(s string) string

ToTitle returns a copy of the string s with all Unicode letters mapped to their Unicode title case.

Example

Code:

// 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"))

Output:

HER ROYAL HIGHNESS
LOUD NOISES
ХЛЕБ

func ToTitleSpecial

func ToTitleSpecial(c unicode.SpecialCase, s string) string

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.

Example

Code:

fmt.Println(strings.ToTitleSpecial(unicode.TurkishCase, "dünyanın ilk borsa yapısı Aizonai kabul edilir"))

Output:

DÜNYANIN İLK BORSA YAPISI AİZONAİ KABUL EDİLİR

func ToUpper

func ToUpper(s string) string

ToUpper returns s with all Unicode letters mapped to their upper case.

Example

Code:

fmt.Println(strings.ToUpper("Gopher"))

Output:

GOPHER

func ToUpperSpecial

func ToUpperSpecial(c unicode.SpecialCase, s string) string

ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their upper case using the case mapping specified by c.

Example

Code:

fmt.Println(strings.ToUpperSpecial(unicode.TurkishCase, "örnek iş"))

Output:

ÖRNEK İŞ

func ToValidUTF8

func ToValidUTF8(s, replacement string) string

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.

func Trim

func Trim(s string, cutset string) string

Trim returns a slice of the string s with all leading and trailing Unicode code points contained in cutset removed.

Example

Code:

fmt.Print(strings.Trim("¡¡¡Hello, Gophers!!!", "!¡"))

Output:

Hello, Gophers

func TrimFunc

func TrimFunc(s string, f func(rune) bool) string

TrimFunc returns a slice of the string s with all leading and trailing Unicode code points c satisfying f(c) removed.

Example

Code:

fmt.Print(strings.TrimFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
    return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))

Output:

Hello, Gophers

func TrimLeft

func TrimLeft(s string, cutset string) string

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.

Example

Code:

fmt.Print(strings.TrimLeft("¡¡¡Hello, Gophers!!!", "!¡"))

Output:

Hello, Gophers!!!

func TrimLeftFunc

func TrimLeftFunc(s string, f func(rune) bool) string

TrimLeftFunc returns a slice of the string s with all leading Unicode code points c satisfying f(c) removed.

Example

Code:

fmt.Print(strings.TrimLeftFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
    return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))

Output:

Hello, Gophers!!!

func TrimPrefix

func TrimPrefix(s, prefix string) string

TrimPrefix returns s without the provided leading prefix string. If s doesn't start with prefix, s is returned unchanged.

Example

Code:

var s = "¡¡¡Hello, Gophers!!!"
s = strings.TrimPrefix(s, "¡¡¡Hello, ")
s = strings.TrimPrefix(s, "¡¡¡Howdy, ")
fmt.Print(s)

Output:

Gophers!!!

func TrimRight

func TrimRight(s string, cutset string) string

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.

Example

Code:

fmt.Print(strings.TrimRight("¡¡¡Hello, Gophers!!!", "!¡"))

Output:

¡¡¡Hello, Gophers

func TrimRightFunc

func TrimRightFunc(s string, f func(rune) bool) string

TrimRightFunc returns a slice of the string s with all trailing Unicode code points c satisfying f(c) removed.

Example

Code:

fmt.Print(strings.TrimRightFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
    return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))

Output:

¡¡¡Hello, Gophers

func TrimSpace

func TrimSpace(s string) string

TrimSpace returns a slice of the string s, with all leading and trailing white space removed, as defined by Unicode.

Example

Code:

fmt.Println(strings.TrimSpace(" \t\n Hello, Gophers \n\t\r\n"))

Output:

Hello, Gophers

func TrimSuffix

func TrimSuffix(s, suffix string) string

TrimSuffix returns s without the provided trailing suffix string. If s doesn't end with suffix, s is returned unchanged.

Example

Code:

var s = "¡¡¡Hello, Gophers!!!"
s = strings.TrimSuffix(s, ", Gophers!!!")
s = strings.TrimSuffix(s, ", Marmots!!!")
fmt.Print(s)

Output:

¡¡¡Hello

type Builder

type Builder struct {
    // contains filtered or unexported fields
}

A Builder is used to efficiently build a string using Write methods. It minimizes memory copying. The zero value is ready to use. Do not copy a non-zero Builder.

Example

Code:

var b strings.Builder
for i := 3; i >= 1; i-- {
    fmt.Fprintf(&b, "%d...", i)
}
b.WriteString("ignition")
fmt.Println(b.String())

Output:

3...2...1...ignition

func Builder.Cap

func (b *Builder) Cap() int

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.

func Builder.Grow

func (b *Builder) Grow(n int)

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.

func Builder.Len

func (b *Builder) Len() int

Len returns the number of accumulated bytes; b.Len() == len(b.String()).

func Builder.Reset

func (b *Builder) Reset()

Reset resets the Builder to be empty.

func Builder.String

func (b *Builder) String() string

String returns the accumulated string.

func Builder.Write

func (b *Builder) Write(p []byte) (int, error)

Write appends the contents of p to b's buffer. Write always returns len(p), nil.

func Builder.WriteByte

func (b *Builder) WriteByte(c byte) error

WriteByte appends the byte c to b's buffer. The returned error is always nil.

func Builder.WriteRune

func (b *Builder) WriteRune(r rune) (int, error)

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.

func Builder.WriteString

func (b *Builder) WriteString(s string) (int, error)

WriteString appends the contents of s to b's buffer. It returns the length of s and a nil error.

type Reader

type Reader struct {
    // contains filtered or unexported fields
}

A Reader implements the io.Reader, io.ReaderAt, io.Seeker, io.WriterTo, io.ByteScanner, and io.RuneScanner interfaces by reading from a string. The zero value for Reader operates like a Reader of an empty string.

func NewReader

func NewReader(s string) *Reader

NewReader returns a new Reader reading from s. It is similar to bytes.NewBufferString but more efficient and read-only.

func Reader.Len

func (r *Reader) Len() int

Len returns the number of bytes of the unread portion of the string.

func Reader.Read

func (r *Reader) Read(b []byte) (n int, err error)

func Reader.ReadAt

func (r *Reader) ReadAt(b []byte, off int64) (n int, err error)

func Reader.ReadByte

func (r *Reader) ReadByte() (byte, error)

func Reader.ReadRune

func (r *Reader) ReadRune() (ch rune, size int, err error)

func Reader.Reset

func (r *Reader) Reset(s string)

Reset resets the Reader to be reading from s.

func Reader.Seek

func (r *Reader) Seek(offset int64, whence int) (int64, error)

Seek implements the io.Seeker interface.

func Reader.Size

func (r *Reader) Size() int64

Size returns the original length of the underlying string. Size is the number of bytes available for reading via ReadAt. The returned value is always the same and is not affected by calls to any other method.

func Reader.UnreadByte

func (r *Reader) UnreadByte() error

func Reader.UnreadRune

func (r *Reader) UnreadRune() error

func Reader.WriteTo

func (r *Reader) WriteTo(w io.Writer) (n int64, err error)

WriteTo implements the io.WriterTo interface.

type Replacer

type Replacer struct {
    // contains filtered or unexported fields
}

Replacer replaces a list of strings with replacements. It is safe for concurrent use by multiple goroutines.

func NewReplacer

func NewReplacer(oldnew ...string) *Replacer

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.

Example

Code:

r := strings.NewReplacer("<", "&lt;", ">", "&gt;")
fmt.Println(r.Replace("This is <b>HTML</b>!"))

Output:

This is &lt;b&gt;HTML&lt;/b&gt;!

func Replacer.Replace

func (r *Replacer) Replace(s string) string

Replace returns a copy of s with all replacements performed.

func Replacer.WriteString

func (r *Replacer) WriteString(w io.Writer, s string) (n int, err error)

WriteString writes s to w with all replacements performed.