Is there a command for checking alias existence in PowerShell?

Question

Is there a PowerShell command that allows you to check to see if an alias exists or not?

(I have been looking around on the web, and it doesn't look like it.)

Answer 1

You can use Test-Path for this:

PS C:\> test-path alias:l*
True
PS C:\> test-path alias:list*
False

Just use:

if (Test-Path alias:list*) { ... }

or

if(!(Test-Path alias:list*)) { ... }

if you want to do something when the alias doesn't exist.

As others wrote, Get-Alias works as well, but Test-Path will avoid building the list of aliases so might be every so slightly faster if you care about that.

Further explanation:

Powershell uses path names to access a lot more than just files, so while C: prefix lets you access files on drive C, alias: lets you access aliases, and other qualifers let you access things like functions, commands, registry keys, security certificates, and so on. So here, alias:l* is a wildcard pathname which will match all aliases that begin with the letter l in exactly the same way that C:l* would match all files beginning with l in the root of drive C.

Test-Path is a commandlet which tests whether the path refers to an existing object with a True result only if at least one existing object matches that path. So normally you would use it to test whether a file exists but equally you can test for existence of anything that is addressable with a suitable qualifier.

Answer 2

I think Get-Alias is what you are looking for.

MS Documentation: http://technet.microsoft.com/en-gb/library/ee176839.aspx

Example for IF:

$ar = get-alias -name f* 
if($ar.count -lt 1){ do stuff }

Answer 3

Yes, use the Get-Alias command.

Example:

Get-Alias -Name spps;

# If statement example
if (Get-Alias -Name spps) {
    # Do something here
}

To get a list of all commands that deal with aliases, use Get-Command

Get-Command -Name *alias;

Answer 4

There is a provider just for Aliases, and an Alias: location, so you can also use Get-Childitem.

Get-Childitem alias: 

Answer 5

Another option if you are just wanting to set an alias if it does not already exist is to use the -Force parameter in Set-Alias, so you do not get an error saying the alias already exists:

Set-Alias "foo" MyFooFunction -Force

Things like if(!(Get-Alias -Name foo)) error if the alias does not exist.

Answer 6

(tested in version 5)

Here is how I use the above (Big thanks to all!):

If ((Test-Path alias:foo) -eq $false) {New-Alias -name foo -value Get-Foo}

This is at the bottom of every script that is or will become a module. It puts an alias on the user's system without throwing an error or overwriting an existing alias if the alias already exists.

Answer 7

Inspired from answers provided by Duncan and Dana, I have created the following function. i recommend adding it to the file pointed by your PowerShell's $PROFILE variable.

function New-AliasSafe {
    param(
        [Parameter(Mandatory=$true)]
        [string]
        $Name,

        [Parameter(Mandatory=$true)]
        [string]
        $Value
    )

    if (!(Test-Path alias:$Name)) {
        New-Alias -Name $Name -Value $Value -Scope Global
        Write-Verbose "Alias $Name created successfully!"
    } else {
        Write-Verbose "Another alias with $Name already exists!"
    }
}

Now you can just call this function whenever you want to import an alias.

New-AliasSafe -Name wo -Value Write-Output

If you want to know whether the alias was successfully created or not, you can call this function like this instead.

New-AliasSafe -Name wo -Value Write-Output -Verbose

Answer 8

Just wanted to add yet another way to achieve this..

$ErrorActionPreference = 'Stop'
$ee = @() # Exception catcher
$Newalias = 'wv'
try{
New-Alias -Name $Newalias -Value Write-Verbose | Out-Null
}
catch{$ee += $_}

if (($ee -ne $null) -and ($ee.CategoryInfo.Category.ToString() -match 'ResourceExists')){Write-Warning "Alias $Newalias already exists";break}
else{Write-Verbose 'Continue on'}

Catch the exception and check if that matches the condition for the Boolean logic of existence. I've found this works well unless the exception is different than you were expecting.