In PowerShell how do I test whether or not a specific variable exists in global scope

Question

I m using PowerShell scripts for some UI automation of a WPF application   Normally  the scripts are run as a group  based on the value of a global variable   It s a little inconvenient to set this variable manually for the times when I want to run just one script  so I m looking for a way to modify them to check for this variable and set it if not found   test-path variable  foo doesn t seem to work  since I still get the following error      The variable   global foo  cannot be retrieved because it has not been set

User · Answer

Test the existence of variavle MyVariable  Returns boolean true or false  Test-Path variable  MyVariable

User · Answer

EDIT  Use stej s answer below  My own  partially incorrect  one is still reproduced here for reference     You can use  Get-Variable foo -Scope Global   and trap the error that is raised when the variable doesn t exist

User · Answer

Personal preference is to use Ignore over SilentlyContinue here because it s not an error at all  Since we re expecting it to potentially be  false let s prevent it  with Ignore  from being put  albeit silently  in the  Error stack   You can use   if  Get-Variable  foo  -Scope  Global  -ErrorAction  Ignore          true   else        false     More tersely    bool  gv foo -s global -ea ig    Output of either   False   Alternatively  You can trap the error that is raised when the variable doesn t exist   try       Get-Variable foo -Scope Global -ErrorAction  Stop    catch  System Management Automation ItemNotFoundException        Write-Warning        Outputs   WARNING  Cannot find a variable with the name  foo

User · Answer

So far  it looks like the answer that works is this one   To break it out further  what worked for me was this   Get-Variable -Name foo -Scope Global -ea SilentlyContinue   out-null     returns either true or false

User · Answer

You can assign a variable to the return value of Get-Variable then check to see if it is null    variable   Get-Variable -Name foo -Scope Global -ErrorAction SilentlyContinue  if   variable -eq  null        Write-Host  foo does not exist       else      Just be aware that the variable has to be assigned to something for it to  exist   For example    global foo    null   variable   Get-Variable -Name foo -Scope Global -ErrorAction SilentlyContinue  if   variable -eq  null        Write-Host  foo does not exist    else       Write-Host  foo exists      global bar   variable   Get-Variable -Name bar -Scope Global -ErrorAction SilentlyContinue  if   variable -eq  null        Write-Host  bar does not exist    else       Write-Host  bar exists      Output   foo exists bar does not exist

User · Answer

There s an even easier way   if   variable        Write-Host  bar exist    else       Write-Host  bar does not exists

User · Answer

Simple   boolean  get-variable  Varname  -ErrorAction SilentlyContinue

User · Answer

myvar   if   env variable     env variable   else    default value

User · Answer

Test-Path can be used with a special syntax   Test-Path variable global foo   This also works for environment variables   env foo    Test-Path env foo   And for non-global variables  just  foo inline    Test-Path variable foo

[powershell] In PowerShell, how do I test whether or not a specific variable exists in global scope?

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