Скрипт не работает...

---------------BEGIN-------------------- while sleep 10 do if ping -q -c 2 192.168.0.50 >> /dev/null; then if [ $s = 0 ] then echo YES | xmessage -file - -center -buttons Ok:1 -font '-microsoft-tahoma-medium-r-normal-*-*-120-*-*-p-*-koi8-u' -fg yellow -bg navy & fi s = 1 else if [ $s = 1 ] then echo NO | xmessage -file - -center -buttons Ok:1 -font '-microsoft-tahoma-medium-r-normal-*-*-120-*-*-p-*-koi8-u' -fg yellow -bg navy & fi s = 0 fi done -------------END-------------------------------- bash# cd bin bash# ./script ./pwait: line 12: [: =: unary operator expected ./pwait: line 16: s: command not found