Is Value Null (is-null)
About 1 min
is-null
)
Is Value 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.