40+ practical string tips [cheat sheet]

yourbasic.org/golang

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" \xNN specifies a byte
"\u65E5" \uNNNN specifies a Unicode value
"\\" \ Backslash
"\"" " Double quote
"\n" Newline
"\t" Tab
`\xe6` \xe6 Raw string literal*
html.EscapeString("<>") &lt;&gt; 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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