String Functions

The standard library's strings package provides many useful string-related functions. Here are some examples to give you a sense of the package.

package main

import (
	"fmt"
	s "strings"
)

We alias fmt.Println to a shorter name as we'll use it a lot below.

var p = fmt.Println

func main() {

Here's a sample of the functions available in strings. Since these are functions from the package, not methods on the string object itself, we need to pass the string in question as the first argument to the function.

	p("Contains:  ", s.Contains("test", "es"))
	p("Count:     ", s.Count("test", "t"))
	p("HasPrefix: ", s.HasPrefix("test", "te"))
	p("HasSuffix: ", s.HasSuffix("test", "st"))
	p("Index:     ", s.Index("test", "e"))
	p("Join:      ", s.Join([]string{"a", "b"}, "-"))
	p("Repeat:    ", s.Repeat("a", 5))
	p("Replace:   ", s.Replace("foo", "o", "0", -1))
	p("Replace:   ", s.Replace("foo", "o", "0", 1))
	p("Split:     ", s.Split("a-b-c-d-e", "-"))
	p("ToLower:   ", s.ToLower("TEST"))
	p("ToUpper:   ", s.ToUpper("test"))

Trimming and splitting on whitespace.

	p("TrimSpace: ", s.TrimSpace("  padded  "))
	p("Trim:      ", s.Trim("--x--", "-"))
	p("TrimPrefix:", s.TrimPrefix("v1.2", "v"))
	p("Fields:    ", s.Fields("  a  b c "))

Cut splits around the first separator and reports whether it was found.

	key, val, ok := s.Cut("name=gopher", "=")
	p("Cut:       ", key, val, ok)

EqualFold compares case-insensitively.

	p("EqualFold: ", s.EqualFold("Go", "GO"))

strings.Builder builds a string efficiently, without copying on every +.

	var b s.Builder
	for i := range 3 {
		fmt.Fprintf(&b, "%d,", i)
	}
	b.WriteString("done")
	p("Builder:   ", b.String())

A Replacer performs several replacements in one pass.

	r := s.NewReplacer("<", "&lt;", ">", "&gt;")
	p("Replacer:  ", r.Replace("<b>hi</b>"))
}

$ go run ./54_string_functions
Contains:   true
Count:      2
HasPrefix:  true
HasSuffix:  true
Index:      1
Join:       a-b
Repeat:     aaaaa
Replace:    f00
Replace:    f0o
Split:      [a b c d e]
ToLower:    test
ToUpper:    TEST
TrimSpace:  padded
Trim:       x
TrimPrefix: 1.2
Fields:     [a b c]
Cut:        name gopher true
EqualFold:  true
Builder:    0,1,2,done
Replacer:   &lt;b&gt;hi&lt;/b&gt;

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