Is Value Null (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"
}

See Also

• Define Environmental Variable (export): Define an environmental variable and set it's value
• Define Global (global): Define a global variable and set it's value
• Define Variable (set): Define a variable (typically local) and set it's value
• Reserved Variables: Special variables reserved by Murex
• Variable And Config Scoping: How scoping works within Murex
• ?? Null Coalescing Operator: Returns the right operand if the left operand is empty / undefined (expression)

---

This document was generated from builtins/core/typemgmt/isnull_doc.yaml.