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strings package - strings - Go Packages

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.

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This section is empty.

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. 

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))
}

Output:

true
false

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. 

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"))
}

Output:

-1
0
1

Contains reports whether substr is within s. 

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("", ""))
}

Output:

true
false
true
true

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

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("", ""))
}

Output:

false
true
true
true
false
false

ContainsFunc reports whether any Unicode code points r within s satisfy f(r). 

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))
}

Output:

true
false

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

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))
}

Output:

true
false

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. 

package main

import (
	"fmt"
	"strings"
)

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

Output:

3
5

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. 

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")
}

Output:

Cut("Gopher", "Go") = "", "pher", true
Cut("Gopher", "ph") = "Go", "er", true
Cut("Gopher", "er") = "Goph", "", true
Cut("Gopher", "Badger") = "Gopher", "", 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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	show := func(s, prefix string) {
		after, found := strings.CutPrefix(s, prefix)
		fmt.Printf("CutPrefix(%q, %q) = %q, %v\n", s, prefix, after, found)
	}
	show("Gopher", "Go")
	show("Gopher", "ph")
}

Output:

CutPrefix("Gopher", "Go") = "pher", true
CutPrefix("Gopher", "ph") = "Gopher", false

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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	show := func(s, suffix string) {
		before, found := strings.CutSuffix(s, suffix)
		fmt.Printf("CutSuffix(%q, %q) = %q, %v\n", s, suffix, before, found)
	}
	show("Gopher", "Go")
	show("Gopher", "er")
}

Output:

CutSuffix("Gopher", "Go") = "Gopher", false
CutSuffix("Gopher", "er") = "Goph", 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. 

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
}

Output:

true
true
false

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. Every element of the returned slice is non-empty. Unlike Split, leading and trailing runs of white space characters are discarded. 

package main

import (
	"fmt"
	"strings"
)

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

Output:

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

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. Every element of the returned slice is non-empty. Unlike Split, leading and trailing runs of code points satisfying f(c) are discarded.

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. 

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))
}

Output:

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

FieldsFuncSeq returns an iterator over substrings of s split around runs of Unicode code points satisfying f(c). The iterator yields the same strings that would be returned by FieldsFunc(s), but without constructing the slice. 

package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	text := "The quick brown fox"
	fmt.Println("Split on whitespace(similar to FieldsSeq):")
	for word := range strings.FieldsFuncSeq(text, unicode.IsSpace) {
		fmt.Printf("%q\n", word)
	}

	mixedText := "abc123def456ghi"
	fmt.Println("\nSplit on digits:")
	for word := range strings.FieldsFuncSeq(mixedText, unicode.IsDigit) {
		fmt.Printf("%q\n", word)
	}

}

Output:

Split on whitespace(similar to FieldsSeq):
"The"
"quick"
"brown"
"fox"

Split on digits:
"abc"
"def"
"ghi"

FieldsSeq returns an iterator over substrings of s split around runs of whitespace characters, as defined by unicode.IsSpace. The iterator yields the same strings that would be returned by Fields(s), but without constructing the slice. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	text := "The quick brown fox"
	fmt.Println("Split string into fields:")
	for word := range strings.FieldsSeq(text) {
		fmt.Printf("%q\n", word)
	}

	textWithSpaces := "  lots   of   spaces  "
	fmt.Println("\nSplit string with multiple spaces:")
	for word := range strings.FieldsSeq(textWithSpaces) {
		fmt.Printf("%q\n", word)
	}

}

Output:

Split string into fields:
"The"
"quick"
"brown"
"fox"

Split string with multiple spaces:
"lots"
"of"
"spaces"

HasPrefix reports whether the string s begins with prefix. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.HasPrefix("Gopher", "Go"))
	fmt.Println(strings.HasPrefix("Gopher", "C"))
	fmt.Println(strings.HasPrefix("Gopher", ""))
}

Output:

true
false
true

HasSuffix reports whether the string s ends with suffix. 

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", ""))
}

Output:

true
false
false
true

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

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.Index("chicken", "ken"))
	fmt.Println(strings.Index("chicken", "dmr"))
}

Output:

4
-1

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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.IndexAny("chicken", "aeiouy"))
	fmt.Println(strings.IndexAny("crwth", "aeiouy"))
}

Output:

2
-1

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

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'))
}

Output:

0
3
-1

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

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))
}

Output:

7
-1

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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.IndexRune("chicken", 'k'))
	fmt.Println(strings.IndexRune("chicken", 'd'))
}

Output:

4
-1

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. 

package main

import (
	"fmt"
	"strings"
)

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

Output:

foo, bar, baz

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

Output:

0
3
-1

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. 

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"))
}

Output:

4
8
-1

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

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'))
}

Output:

10
8
-1

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

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))
}

Output:

5
2
-1

Lines returns an iterator over the newline-terminated lines in the string s. The lines yielded by the iterator include their terminating newlines. If s is empty, the iterator yields no lines at all. If s does not end in a newline, the final yielded line will not end in a newline. It returns a single-use iterator. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	text := "Hello\nWorld\nGo Programming\n"
	for line := range strings.Lines(text) {
		fmt.Printf("%q\n", line)
	}

}

Output:

"Hello\n"
"World\n"
"Go Programming\n"

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. 

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..."))
}

Output:

'Gjnf oevyyvt naq gur fyvgul tbcure...

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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println("ba" + strings.Repeat("na", 2))
}

Output:

banana

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. 

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))
}

Output:

oinky oinky oink
moo moo moo

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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ReplaceAll("oink oink oink", "oink", "moo"))
}

Output:

moo moo moo

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. 

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"))
}

Output:

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

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. 

package main

import (
	"fmt"
	"strings"
)

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

Output:

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

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. 

package main

import (
	"fmt"
	"strings"
)

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

Output:

["a," "b,c"]

SplitAfterSeq returns an iterator over substrings of s split after each instance of sep. The iterator yields the same strings that would be returned by SplitAfter(s, sep), but without constructing the slice. It returns a single-use iterator. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	s := "a,b,c,d"
	for part := range strings.SplitAfterSeq(s, ",") {
		fmt.Printf("%q\n", part)
	}

}

Output:

"a,"
"b,"
"c,"
"d"

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. 

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)
}

Output:

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

SplitSeq returns an iterator over all substrings of s separated by sep. The iterator yields the same strings that would be returned by Split(s, sep), but without constructing the slice. It returns a single-use iterator. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	s := "a,b,c,d"
	for part := range strings.SplitSeq(s, ",") {
		fmt.Printf("%q\n", part)
	}

}

Output:

"a"
"b"
"c"
"d"

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. 

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("брат"))
}

Output:

Her Royal Highness
Loud Noises
Брат

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

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ToLower("Gopher"))
}

Output:

gopher

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

package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	fmt.Println(strings.ToLowerSpecial(unicode.TurkishCase, "Örnek İş"))
}

Output:

örnek iş

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

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("брат"))
}

Output:

HER ROYAL HIGHNESS
LOUD NOISES
БРАТ

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. 

package main

import (
	"fmt"
	"strings"
	"unicode"
)

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

Output:

DÜNYANIN İLK BORSA YAPISI AİZONAİ KABUL EDİLİR

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

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ToUpper("Gopher"))
}

Output:

GOPHER

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

package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	fmt.Println(strings.ToUpperSpecial(unicode.TurkishCase, "örnek iş"))
}

Output:

ÖRNEK İŞ

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. 

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"))
}

Output:

abc
abc
abc

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

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Print(strings.Trim("¡¡¡Hello, Gophers!!!", "!¡"))
}

Output:

Hello, Gophers

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

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)
	}))
}

Output:

Hello, Gophers

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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Print(strings.TrimLeft("¡¡¡Hello, Gophers!!!", "!¡"))
}

Output:

Hello, Gophers!!!

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

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)
	}))
}

Output:

Hello, Gophers!!!

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

package main

import (
	"fmt"
	"strings"
)

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

Output:

Gophers!!!

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. 

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Print(strings.TrimRight("¡¡¡Hello, Gophers!!!", "!¡"))
}

Output:

¡¡¡Hello, Gophers

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

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)
	}))
}

Output:

¡¡¡Hello, Gophers

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

package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.TrimSpace(" \t\n Hello, Gophers \n\t\r\n"))
}

Output:

Hello, Gophers

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

package main

import (
	"fmt"
	"strings"
)

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

Output:

¡¡¡Hello

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. 

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())

}

Output:

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

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 (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 (b *Builder) Len() int

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

func (b *Builder) Reset()

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.

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.

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

func (r *Reader) Len() int

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

Reset resets the Reader to be reading from s.

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.

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

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. 

package main

import (
	"fmt"
	"strings"
)

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

Output:

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

Replace returns a copy of s with all replacements performed.

WriteString writes s to w with all replacements performed.