Assign Default Values to PowerShell Variables: Both Literals and Expressions.

The aim of this playbook🏁 is to demonstrate the assignment of a default value to a variable of a powershell function. For comparison in Python you do the assignment within parameter declaration:

def foo(bar="xxx"):
    print(bar)
foo()
>>> xxx

1. answer

• for shorthanded style, identical to python’s syntax
• just assign the default value to the parameter: function foo($t = "bar") {write-host $t}

foo
> "bar"

• for long-handed style, use param keyword
• put the the $paramName = defaultValue into parenthesis right after the code block begins
• use function <funcName> {param($foo = <defaultValue>) <code>}
• see example2 for an expression as a default value

2. default value as literal

• the example function opens The Most Dangerous Writing App with the duration of 1 minute

function start-writing {
    param($len = 1)
    $url = "https://www.squibler.io/dangerous-writing-prompt-app/write?limit=$len&type=minutes"
    start chrome $url
}

3. default value as an expression

Function rdbl {
    param (
        [string]$timestamp = ((Get-Date) - (New-TimeSpan -Days 1)).ToString("yyyy-MM-dd")
    )
    Write-Host $timestamp
}
▶ rdbl
2021-09-10
▶ rdbl -timestamp 2021-09-01
2021-09-01

4. sources

• Designing Professional Parameters — powershell.one
• The Most Dangerous Writing App