PowerShell: Comparing Version Numbers

Comparing applciation version number in PowerShell would come in handy when Selenium is used to automate Chrome. The version of Selenium which allows Chrome to be automated is dependent on the version of Chrome installed on a give host (see PowerShell: Geting Chrome's Version Number). By using Chrome's version number, it would be possible for PowerShell to load at runtime the correct version of Selenium to allow the particular version of Chrome to be automated.

Comparing Versions

When thought of as version numbers 1.0.100 is a newer version than 1.0.99 but below the are compared as strings:

[string] $versionPrevious = '1.0.99'
[string] $versionCurrent = '1.0.100'

if ($versionCurrent -gt $versionPrevious) {

    Write-Host 

      "Correct: `$versionCurrent ($versionCurrent) -gt" + 

      "`$versionPrevious ($versionPrevious)"

}

else {

    Write-Host 

      "Incorrect: `$versionPrevious ($versionPrevious) -gt" +

      " `$versionCurrent ($versionCurrent)"

}

The output from the previous code is as expected the result of a string compare using the -gt operator which is not the same a comparison between version numbers:

Incorrect: $versionPrevious (1.0.99) -gt $versionCurrent (1.0.100)
.NET provides a class System.Version for representing version numbers. In PowerShell this calls is presented by the type [version]. The System.NET version type is described by Microsoft in https://docs.microsoft.com/ as follows:

Changing the variable type from [string] to [version] results in the version numbers be compared correctly:

[version] $versionPrevious = '1.0.99'
[version] $versionCurrent = '1.0.100'

if ($versionCurrent -gt $versionPrevious) {

    Write-Host 

      "Correct: `$versionCurrent ($versionCurrent) -gt" + 

      "`$versionPrevious ($versionPrevious)"

}

else {

    Write-Host 

      "Incorrect: `$versionPrevious ($versionPrevious) -gt" +

      " `$versionCurrent ($versionCurrent)"

}

The output from the previous code is as expected the result of a version using the -gt operator:

Correct: $versionCurrent (1.0.100) -gt $versionPrevious (1.0.99)

A final note, the Escape Character

The previous code snippet contained two instance of the back quote character being used to suppress the $ character's use in a double quoted string `$versionCurrent and `$versionCurrent. A PowerShell variable inside of a double quoted string is results in the value of the variable being replaced inside the string. The back quote before $ suppresses this substitution