Get current versions for activated features (not feature definitions) in a web or site collection

Recently I wrote a PowerShell-Script which writes the current version-numbers of web-features specified by a name-filter into a file. These versions are not from the feature-definition but from the feature activated in a web.

An example for this could be the following:
On a SharePoint-server a feature named custom_feature_1 was installed which has a version of 3.0.0.0 because it's been updated a few times during the lifecycle of the appication.
Because the rootweb was created first, the feature's version is 1.0.0.0 there. A newer subweb below has been created after the feature was updated and there the feature's version is 2.0.0.0. Now, after the third update, another web will be created where the feature now has a version of 3.0.0.0.

So how can you easily get the version of the feature activated in one of these webs?

You can use this PowerShell-script to get all information about your features:

get-spweb http://customsitecollection/customweb |% {$_.Features} | where-object {$_.Definition -ne $null} | where-object {$_.Definition.DisplayName.StartsWith("custom")} |% {new-object psobject -Property @{Id = $_.DefinitionId; Version = $_.Version; DisplayName = ($_ | select -ExpandProperty Definition).DisplayName; Scope = ($_ | select -ExpandProperty Definition).Scope; }} | format-table -Property * -Autosize | Out-String -Width 120 | out-file custom_web_features.txt


Just copy these lines and replace the bold-marked parts by your own needs:
http://customsite/customweb - The full path to the web you want the feature-versions from
custom - The name that the features starts with in SharePoint-Root features-folder
custom_web_features.txt - The name of the file that's created with information

The content of the file should look like this:

You can reuse the script for site-scoped features too. Just replace get-spweb by get-spsite and a valid URL to a sitecollection.