sysl.env

Index

get get_or is_set

Functions

get

get(name: string) -> Option[string]

What a name is set to, or None where it is unset.

A value that is not UTF-8 answers None as well, which folds a third case into the second and is the honest thing for a function whose result is a string: the bytes are somebody’s environment rather than the program’s input, so there is no encoding to negotiate and nothing useful to report. A caller that must tell “unset” from “not text” asks is_set too.

get_or

get_or(name: string, fallback: string) -> string

What a name is set to, or a value of the caller’s where it is not.

This is the shape most callers actually want – a default that is a real value rather than a case to match – and it is the one sysl.posix.time uses to let TZDIR redirect a lookup.

is_set

is_set(name: string) -> bool

Whether a name is present at all, whatever it holds.

Set-to-empty answers true here and Some("") from get, which is what makes the two functions worth having separately: VAR= is a name that is set, and a convention reading presence rather than content is entitled to say so.