Splitting a String into a Slice in Golang

I can’t begin to tell you how often I split strings in Go. More often than not I’m just parsing a comma-separated list from an environment variable, and Go’s standard library gives us some great tools for that kind of manipulation.

Before we get too far, let me mention that I recently launched Go Mastery, a hands-on Golang course. Give it a shot if you want to learn more about Go, now let’s get back to string splitting.

Table of Contents

Split by commas or other delimiters

strings.Split()

Go’s rich standard library makes it easy to split a string into a slice. 99% of the time you need to split strings in Go, you’ll want the strings package’s strings.Split() function.

package main

import (
    "fmt"
    "strings"
)

func main() {
    fruitsString := "apple,banana,orange,pear"
    fruits := strings.Split(fruitsString, ",")
    fmt.Println(fruits)
    // prints ["apple", "banana", "orange", "pear"]
}

The Split function takes a string and a delimiter as parameters and returns a slice of strings where each substring was formally separated by the given delimiter.

strings.SplitN()

The strings.SplitN() function takes three arguments: the string to be split, a separator, and the number of resulting strings in the slice.

To be honest, I don’t use this function very often, but it could be useful under niche circumstances, For example, maybe you’re working on a large document and only care about the first part of the text.

package main

import (
    "fmt"
    "strings"
)

func main() {
    fruitsString := "apple.banana.orange.pear"
    fruits := strings.SplitN(fruitsString, ".", 3)
    fmt.Println(fruits)
    // prints ["apple", "banana", "orange.pear"]
}

Split by delimiters and retain the delimiters

strings.SplitAfter()

Similar to Split(), the SplitAfter() function splits the original string but leaves the delimiters at the end of each substring.

package main

import (
    "fmt"
    "strings"
)

func main() {
    fruitsString := "apple.banana.orange.pear"
    fruits := strings.SplitAfter(fruitsString, ".")
    fmt.Println(fruits)
    // prints ["apple.", "banana.", "orange.", "pear"]
}

strings.SplitAfterN()

SplitAfterN does the same thing as SplitAfter except it only splits the first N substrings. Everything else is retained in the final substring.

package main

import (
    "fmt"
    "strings"
)

func main() {
    fruitsString := "apple.banana.orange.pear"
    fruits := strings.SplitAfterN(fruitsString, ".", 2)
    fmt.Println(fruits)
    // prints ["apple.", "banana.orange.pear"]
}

Split by whitespace and newlines

The strings package can do more than just separate a string based on a provided delimiter. The strings.Fields() function will split on all whitespace, and exclude it from the final result. This is useful if you don’t care about the kind of whitespace, for example, tabs, spaces, and newlines all count as whitespace.

package main

import (
    "fmt"
    "strings"
)

func main() {
    fmt.Printf("Fields are: %q", strings.Fields(`apple
     banana orange
     pear
     `))
    // prints ["apple", "banana", "orange", "pear"]
}

Split using a regex

Regular expressions are a popular way to manipulate strings, and Go’s built-in regex engine can help us out. We don’t even need to use the strings package here, instead we’ll use the regexp package.

package main

import (
    "fmt"
    "regexp"
)

func main() {
    s := regexp.MustCompile("[0-9]").Split("apple1banana2orange3pear", -1)
    fmt.Println(s)
    // prints ["apple", "banana", "orange", "pear"]
}

Gotcha – Strings in Go are special

Be aware when you’re working with a lot of strings that Go treats strings differently than other languages like Java, C, and Python. Strings in Go are read-only slices of bytes, and those bytes are arbitrary – they can be anything. Strings in Go are not required to hold Unicode text, UTF-8 text, or any other encoding format.

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Questions?

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