To get current dispay resolution on Linux using shell (bash) you can use default application xrandr.
user@host ~ $ xrandr -d :0 xrandr: Failed to get size of gamma for output default Screen 0: minimum 1824 x 984, current 1824 x 984, maximum 1824 x 984 default connected 1824x984+0+0 0mm x 0mm 1824x984 0.0*