Define Variable (set)
set
)
Define Variable (Define a variable (typically local) and set it's value
Description
Defines, updates or deallocates a variable. By default that variable will be local.
Usage
<stdin> -> set var_name
# Assume value from stdin, define the data type manually
<stdin> -> set datatype var_name
# Define value manually (data type defaults to string; `str`)
set var_name=data
# Define value and data type manually
set datatype var_name=data
# Define a variable but don't set any value
set var_name
set datatype var_name
Examples
As a method
» out "Hello, world!" -> set hw
» out "$hw"
Hello, World!
As a function
» set hw="Hello, world!"
» out "$hw"
Hello, World!
Detail
Deallocation
You can unset variable names with the bang prefix:
!set var_name
Type Annotations
When set
or global
are used as a function, the parameters are passed as a string which means the variables are defined as a str
. If you wish to define them as an alternate data type then you should add type annotations:
» set int age = 30
($age
is an integer, int
)
» global bool dark_theme = true
($dark_theme
is a boolean, bool
)
When using set
or global
as a method, by default they will define the variable as the data type of the pipe:
» open example.json -> set: file
($file
is defined a json
type because open
wrote to set
's pipe with a json
type)
You can also annotate set
and global
when used as a method too:
out 30 -> set: int age
($age
is an integer, int
, despite out
writing a string, `str, to the pipe)
export
does not support type annotations because environmental variables must always be strings. This is a limitation of the current operating systems.
Scoping
Variable scoping is simplified to three layers:
- Local variables (
set
,!set
,let
) - Global variables (
global
,!global
) - Environmental variables (
export
,!export
,unset
)
Variables are looked up in that order of too. For example a the following code where set
overrides both the global and environmental variable:
» set foobar=1
» global foobar=2
» export foobar=3
» out $foobar
1
Local variables
These are defined via set
and let
. They're variables that are persistent across any blocks within a function. Functions will typically be blocks encapsulated like so:
function example {
# variables scoped inside here
}
...or...
private example {
# variables scoped inside here
}
...however dynamic autocompletes, events, unit tests and any blocks defined in config
will also be triggered as functions.
Code running inside any control flow or error handing structures will be treated as part of the same part of the same scope as the parent function:
» function example {
» try {
» # set 'foobar' inside a `try` block
» set foobar=example
» }
» # 'foobar' exists outside of `try` because it is scoped to `function`
» out $foobar
» }
example
Where this behavior might catch you out is with iteration blocks which create variables, eg for
, foreach
and formap
. Any variables created inside them are still shared with any code outside of those structures but still inside the function block.
Any local variables are only available to that function. If a variable is defined in a parent function that goes on to call child functions, then those local variables are not inherited but the child functions:
» function parent {
» # set a local variable
» set foobar=example
» child
» }
»
» function child {
» # returns the `global` value, "not set", because the local `set` isn't inherited
» out $foobar
» }
»
» global $foobar="not set"
» parent
not set
It's also worth remembering that any variable defined using set
in the shells FID (ie in the interactive shell) is localised to structures running in the interactive, REPL, shell and are not inherited by any called functions.
Global variables
Where global
differs from set
is that the variables defined with global
will be scoped at the global shell level (please note this is not the same as environmental variables!) so will cascade down through all scoped code-blocks including those running in other threads.
Environmental variables
Exported variables (defined via export
) are system environmental variables. Inside Murex environmental variables behave much like global
variables however their real purpose is passing data to external processes. For example env
is an external process on Linux (eg /usr/bin/env
on ArchLinux):
» export foo=bar
» env -> grep foo
foo=bar
Function Names
As a security feature function names cannot include variables. This is done to reduce the risk of code executing by mistake due to executables being hidden behind variable names.
Instead Murex will assume you want the output of the variable printed:
» out "Hello, world!" -> set hw
» $hw
Hello, world!
On the rare occasions you want to force variables to be expanded inside a function name, then call that function via exec
:
» set cmd=grep
» ls -> exec $cmd main.go
main.go
This only works for external executables. There is currently no way to call aliases, functions nor builtins from a variable and even the above exec
trick is considered bad form because it reduces the readability of your shell scripts.
Usage Inside Quotation Marks
Like with Bash, Perl and PHP: Murex will expand the variable when it is used inside a double quotes but will escape the variable name when used inside single quotes:
» out "$foo"
bar
» out '$foo'
$foo
» out %($foo)
bar
Synonyms
set
!set
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 - Execute External Command (
exec
): Runs an executable - Expressions (
expr
): Expressions: mathematical, string comparisons, logical operators - Get Item (
[ Index ]
): Outputs an element from an array, map or table - Get Nested Element (
[[ Element ]]
): Outputs an element from a nested structure - Is Value Null (
is-null
): Checks if a variable is null or undefined - Reserved Variables: Special variables reserved by Murex
- Variable and Config Scoping: How scoping works within Murex
%(Brace Quote)
: Initiates or terminates a string (variables expanded)??
Null Coalescing Operator: Returns the right operand if the left operand is empty / undefined (expression)
This document was generated from builtins/core/typemgmt/variables_doc.yaml.