Provided you are connected to a wireless network, then the following one-liner gets you the current signal strength:
PS> @(netsh wlan show interfaces) -match '^\s+Signal' -replace '^\s+Signal\s+:\s+','' 80%
The signal strength is taken from the text output provided by netsh.exe. Embracing it in @() makes sure it always returns an array. The -match operator then uses a regular expression to identify the line that contains the word “Signal” at a line beginning. A following -replace operator uses a regular expression to remove the text that prepends the signal strength.
If you hate regular expressions, you can achieve the same with other strategies, such as this:
PS> (@(netsh wlan show interfaces).Trim() -like 'Signal*').Split(':')[-1].Trim() 80%
Here, each line returned by netsh.exe is first trimmed (removing white space from either end). Next, a classic -like operator selects the line that starts with “Signal”. This line then is splitted by “:”, and the last part (index -1) is used. The signal rating is trimmed again to remove whitespace around it.
Should both commands not return anything, then please check whether your machine is connected to a wireless network at all. You may also want to run the netsh.exe command just with its arguments and without any text operators to view the commands raw output.