Get connected Wi-Fi network signal strength with nmcli

To get the SIGNAL of the AP on which you are connected use:

nmcli dev wifi list | awk '/\*/{if (NR!=1) {print $7}}'

The second * mark in nmcli dev wifi list is set to identify the SSID on which your are connected.

nmcli --version
nmcli tool, version 1.6.2

If you know the name of the network you're connected to, you could modify your approach like this: (for nmcli 1.14.6, other versions may vary)

nmcli -t -f SSID,SIGNAL dev wifi list | grep "^<network name>:" | cut -d : -f 2

The trick here is to use the -f parameter of nmcli to specify what fields you want in your script. If you care about the SSID, use the SSID field; if you care about which one you're connected to, use the IN-USE field:

$ nmcli -f IN-USE,SIGNAL device wifi
*  SIGNAL 
   90
*  73     
   40
$ nmcli -f IN-USE,SIGNAL,SSID device wifi
*  SIGNAL  SSID               
   90      wifiWithoutSpaces
*  73      Some Wifi With Spaces
   40      Wifi With a * in its SSID

The advantage of ordering the fields in this way is that selecting the signal is a fixed number of column-delimiting characters from the start of the row; we can now use GAD3R's answer without running into column count or nmcli versioning issues:

$ nmcli -f IN-USE,SIGNAL,SSID device wifi | awk '/^\*/{if (NR!=1) {print $2}}'
73