Recursively search for a string in all *.txt files:

gci . *.txt -Recurse | select-string -pattern "search-text"

Recursively search for a string in all *.h and *.cpp files:

gci . -Include ( "*.h", "*.cpp" ) -Recurse | select-string -pattern "search-text"

Recursively search for all app.config files and print full path:

gci . -Include ( "app.config" ) -Recurse | % { $_.FullName }

Compute the filesize sum of all of the TXT and XML files in the current directory:

PS:>gci *.txt,*.xml | measure-object -property Length -sum

Look up Powershell Environment Variables:

PS:> ${env:Path}.IndexOf("DoesExist")
26
PS:> ${env:Path}.IndexOf("DoesNotExist")
-1