lix/lix/libexpr/builtins/substring.md

name, args

name	args
substring	start len s

Return the substring of s from character position start (zero-based) up to but not including start + len. If start is greater than the length of the string, an empty string is returned, and if start + len lies beyond the end of the string or len is negative, only the substring up to the end of the string is returned. start must be non-negative. For example,

builtins.substring 0 3 "nixos"

evaluates to "nix", and

builtins.substring 3 (-1) "nixos"

evaluates to "os".