link-a-scalar-to-an-array.md

Link A Scalar To An Array

Zsh has a builtin command typeset that does a variety of things. When given the -T flag and the names of a scalar and an array, it will link them together so that a change to one is reflected in the other.

The scalar is a string of values delimited by a colon (:). The array is an array that can be interacted with using array operations like append (+=).

$ typeset -T FOO foo

$ echo $FOO


$ export FOO="one:two"

$ echo $foo
one two

$ foo+=three

$ echo $FOO
one:two:three

Notice FOO is initially empty. I then export it to overwrite it with two values delimited by a colon. Since foo is automatically kept in sync, I can echo $foo and see those values displayed as an array. I can then append a third value using an array operation on foo. The update will be automatically reflected in FOO.

Zsh does this under the hood for PATH and path which is why you can add to the path via the path array.

See man zshbuiltins for more details.

source