Go string handling overview [cheat sheet]

yourbasic.org/golang

String literals (escape characters)
Concatenate
Equal and compare (ignore case)
Length in bytes or runes
Index, substring, iterate
Search (contains, prefix/suffix, index)
Replace (uppercase/lowercase, trim)
Split by space or comma
Join strings with separator
Format and convert
Regular expressions

String literals (escape characters)

Expression	Result	Note
`""`		Default zero value for type `string`
`"Japan 日本"`	Japan 日本	Go code is Unicode text encoded in UTF‑8
`"\xe6\x97\xa5"`	日	`\xNN` specifies a byte
`"\u65E5"`	日	`\uNNNN` specifies a Unicode value
`"\\"`	\	Backslash
`"\""`	"	Double quote
`"\n"`		Newline
`"\t"`		Tab
`\xe6`	\xe6	Raw string literal*
`html.EscapeString("<>")`	<>	HTML escape for <, >, &, ' and "
`url.PathEscape("A B")`	A%20B	URL percent-encoding net/url

* In `` string literals, text is interpreted literally and backslashes have no special meaning. See Escapes and multiline strings for more on raw strings, escape characters and string encodings.

Concatenate

Expression	Result	Note
`"Ja" + "pan"`	Japan	Concatenation

Performance tips
See 3 tips for efficient string concatenation for how to best use a string builder to concatenate strings without redundant copying.

Equal and compare (ignore case)

Expression	Result	Note
`"Japan" == "Japan"`	true	Equality
`strings.EqualFold("Japan", "JAPAN")`	true	Unicode case folding
`"Japan" < "japan"`	true	Lexicographic order

Length in bytes or runes

Expression	Result	Note
`len("日")`	3	Length in bytes
`utf8.RuneCountInString("日")`	1	in runes unicode/utf8
`utf8.ValidString("日")`	true	UTF-8? unicode/utf8

Index, substring, iterate

Expression	Result	Note
`"Japan"[2]`	'p'	Byte at position 2
`"Japan"[1:3]`	ap	Byte indexing
`"Japan"[:2]`	Ja
`"Japan"[2:]`	pan

A Go range loop iterates over UTF-8 encoded characters (runes):

for i, ch := range "Japan 日本" {
	fmt.Printf("%d:%q ", i, ch)
}
// Output: 0:'J' 1:'a' 2:'p' 3:'a' 4:'n' 5:' ' 6:'日' 9:'本'

Iterating over bytes produces nonsense characters for non-ASCII text:

s := "Japan 日本"
for i := 0; i < len(s); i++ {
	fmt.Printf("%q ", s[i])
}
// Output: 'J' 'a' 'p' 'a' 'n' ' ' 'æ' '\u0097' '¥' 'æ' '\u009c' '¬'

Search (contains, prefix/suffix, index)

Expression	Result	Note
`strings.Contains("Japan", "abc")`	false	Is abc in Japan?
`strings.ContainsAny("Japan", "abc")`	true	Is a, b or c in Japan?
`strings.Count("Banana", "ana")`	1	Non-overlapping instances of ana
`strings.HasPrefix("Japan", "Ja")`	true	Does Japan start with Ja?
`strings.HasSuffix("Japan", "pan")`	true	Does Japan end with pan?
`strings.Index("Japan", "abc")`	-1	Index of first abc
`strings.IndexAny("Japan", "abc")`	1	a, b or c
`strings.LastIndex("Japan", "abc")`	-1	Index of last abc
`strings.LastIndexAny("Japan", "abc")`	3	a, b or c

Replace (uppercase/lowercase, trim)

Expression	Result	Note
`strings.Replace("foo", "o", ".", 2)`	f..	Replace first two “o” with “.” Use -1 to replace all
`f := func(r rune) rune { return r + 1 } strings.Map(f, "ab")`	bc	Apply function to each character
`strings.ToUpper("Japan")`	JAPAN	Uppercase
`strings.ToLower("Japan")`	japan	Lowercase
`strings.Title("ja pan")`	Ja Pan	Initial letters to uppercase
`strings.TrimSpace(" foo\n")`	foo	Strip leading and trailing white space
`strings.Trim("foo", "fo")`		Strip leading and trailing f:s and o:s
`strings.TrimLeft("foo", "f")`	oo	only leading
`strings.TrimRight("foo", "o")`	f	only trailing
`strings.TrimPrefix("foo", "fo")`	o
`strings.TrimSuffix("foo", "o")`	fo

Split by space or comma

Expression	Result	Note
`strings.Fields(" a\t b\n")`	`["a" "b"]`	Remove white space
`strings.Split("a,b", ",")`	`["a" "b"]`	Remove separator
`strings.SplitAfter("a,b", ",")`	`["a," "b"]`	Keep separator

Join strings with separator

Expression	Result	Note
`strings.Join([]string{"a", "b"}, ":")`	a:b	Add separator
`strings.Repeat("da", 2)`	dada	2 copies of “da”

Format and convert

Expression	Result	Note
`strconv.Itoa(-42)`	`"-42"`	Int to string
`strconv.FormatInt(255, 16)`	`"ff"`	Base 16

Sprintf

The fmt.Sprintf function is often your best friend when formatting data:

s := fmt.Sprintf("%.4f", math.Pi) // s == "3.1416"

This fmt cheat sheet covers the most common formatting flags.

Regular expressions

For more advanced string handling, see this Regular expressions tutorial, a gentle introduction to the regexp package with cheat sheet and plenty of examples.

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