How to expand variable in powershell?

Question

Get-WmiObject -Class win32_logicaldisk -Filter 'DeviceID="C:"'

does what I want,

$var="C:"
Get-WmiObject -Class win32_logicaldisk -Filter 'DeviceID="{$var}"'

does nothing. I tried to change the quotes, to concatenate strings, and other 1000 things, but they didn't work. Why the above example doesn't work, and what would work?

Answer 1

When you start a string literal with ' (single-quotes), you're creating a verbatim string - that is, every character inside the string is interpreted literally and variable references and expressions won't expand!

Use " if you want the variable to be expanded:

$var = 'C:'
Get-WmiObject -Class win32_logicaldisk -Filter "DeviceID='$var'"

If your variable name has weird characters, or is followed by a word character, you can qualify the variable name with curly brackets {} immediately after the $:

$var = 'C:'
Get-WmiObject -Class win32_logicaldisk -Filter "DeviceID='${var}'"