Last week a question came across my email about how to find out where a variable came from. I thought this was a great question because I've run into this scenario as well. I see a variable but don't recall what command I typed to create it. What I need is an easy way to find the command so I made a tool.<\/p>\n
Every command you enter in a PowerShell session is stored in an internal history buffer. The number of items is controlled by the automatic variable $MaximumHistoryCount which has a default value of 64. When you run the Get-History command, you can see the list of all your recently run commands. Get-History has an alias of h<\/em>. See a command you want to run again, use Invoke-History, or its alias r<\/em> and specify the item number. With this information, all I need to do is search my history looking for the command that defined the variable in question.<\/p>\n [cc lang=\"PowerShell\"] This would find the command that defined $MyVar. I'm selecting the last history item in case I defined $MyVar earlier. All I care about is the last definition. I'm also using a regular expression so that the command I'm after must start with $MyVar=. Because I'm all about ease of use, I wrapped this core command into a function called Get-VariableDefinition.<\/p>\n [cc lang=\"PowerShell\"] [cmdletBinding()]<\/p>\n Param( Try Catch if ($verify) if ($item) The script file also contains an alias definition. If the variable command can't be found then you get a message. In order to get the most out of this, you should increase your $MaximumHistoryCount variable in your PowerShell profile.<\/p>\n [cc lang=\"PowerShell\"]
\n $item=Get-History -Count $MaximumHistoryCount | where {$_.commandline -match \"^\\`$MyVar=\"} | Select -Last 1
\n[\/cc]<\/p>\n
\nFunction Get-VariableDefinition {<\/p>\n
\n [Parameter(Position=0,Mandatory=$True,HelpMessage=\"Enter a variable name, without the `$\")]
\n [ValidateNotNullOrEmpty()]
\n [string]$Name
\n)<\/p>\n
\n{
\n #make sure a valid variable name was passed
\n $verify=Get-Variable $name -ErrorAction Stop
\n}<\/p>\n
\n{
\n Write-Warning \"The variable $Name was not found.\"
\n}<\/p>\n
\n{
\n #search history and get the last assignment
\n $item=Get-History -Count $MaximumHistoryCount | where {$_.commandline -match \"^\\`$$Name=\"} | Select -Last 1<\/p>\n
\n {
\n #write the Commandline property to the pipeline if something was found
\n $item.CommandLine
\n }
\n else
\n {
\n #the variable definition has expired
\n Write-Host \"Failed to find a definition for `$$Name in your existing history.\" -ForegroundColor Yellow
\n }
\n } #close if $verify
\n} #end Function
\n[\/cc]<\/p>\n
\n[cc lang=\"PowerShell\"]
\nPS S:\\> gvd myvar
\n$myvar=gwmi win32_bios
\nPS S:\\> gvd running
\n$running=gsv | where {$_.status -eq \"running\"}
\nPS S:\\> gvd j
\nFailed to find a definition for $j in your existing history.
\nPS S:\\>
\n[\/cc]<\/p>\n
\n$MaximumHistoryCount=2048
\n[\/cc]<\/p>\n