How to slice string till particular character in Go?

Question

I want to extract a string till a character is found. For example:

message := "Rob: Hello everyone!"
user := strings.Trim(message,

I want to be able to store "Rob" (read till ':' is found).

Answer 1

You may use strings.IndexByte() or strings.IndexRune() to get the position (byte-index) of the colon ':', then simply slice the string value:

message := "Rob: Hello everyone!"
user := message[:strings.IndexByte(message, ':')]
fmt.Println(user)

Output (try it on the Go Playground):

Rob

If you're not sure the colon is in the string, you have to check the index before proceeding to slice the string, else you get a runtime panic. This is how you can do it:

message := "Rob: Hello everyone!"
if idx := strings.IndexByte(message, ':'); idx >= 0 {
    user := message[:idx]
    fmt.Println(user)
} else {
    fmt.Println("Invalid string")
}

Output is the same.

Changing the message to be invalid:

message := "Rob Hello everyone!"

Output this time is (try it on the Go Playground):

Invalid string

Another handy solution is to use strings.Split():

message := "Rob: Hello everyone!"

parts := strings.Split(message, ":")
fmt.Printf("%q\n", parts)

if len(parts) > 1 {
    fmt.Println("User:", parts[0])
}

Output (try it on the Go Playground):

["Rob" " Hello everyone!"]
User: Rob

Should there be no colon in the input string, strings.Split() returns a slice of strings containing a single string value being the input (the code above does not print anything in that case as length will be 1).