PHP: 
[code=php]substr("abcdef", start, length);[/code]
Golang: 
[code=golang]string[start:start+length][/code]

Example: 
PHP:
[code=php]substr("abcdef", 2, 3);[/code]
Golang:
[code=golang]fmt.Print("abcdef"[2:5])[/code]