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`is-null`

Checks if a variable is null or undefined

Description

is-null checks if a variable is null or undefined. If multiple variables are passed in is-null’s parameters, the exit number will be a count of the number of non-null variables checked.

is-null is intended to be run non-interactively, where it doesn’t write to stdout but instead communicates its results via exit number. However if stdout is a TTY is-null will additionally write to the terminal.

The following conditions are considered “null” by is-null:

a variable not being defined
a property not existed, eg an object key or array index
any other error reading from a variable
or the value of the variable or property being the data-type null or a value of null.

Zero length strings, strings containing the word “null” and numeric data types (eg num, int, float with the value of 0) are all not null.

Usage

is-null variable_name... -> <stdout>

Examples

Interactive output

» $baz = ""
» is-null foo bar baz
foo: undefined or null
bar: undefined or null
baz: defined and not null

None interactive output

if { is-null foobar } then {
    out "baz is undefined"
}

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