Shell Programming and Scripting

hour=$1 
echo "hour:$hour" 
if [ $hour -ge 3 ]  &&  ! [[ $hour -ge 12] && [$hour -le 15 ]]; then 
echo "exit" 
else 
echo "enter" 
fi

$ ./test.sh 13 hour:13 ./test.sh: 
line 3: [[: 12]: syntax error: invalid arithmetic operator (error token is "]") exit

if [ $hour -ge 3 ]  && ! [ $hour -ge 12 -a $hour -le 15 ]; then

$ cat ts1
hour=$1
echo "hour:$hour"
if [ $hour -ge 3 ] && ( ! [[ $hour -ge 12 && $hour -le 15 ]] ); then
echo "exit"
else
echo "enter"
fi

$ for i in {0..23}; do ksh ts1 $i; done
hour:0
enter
hour:1
enter
hour:2
enter
hour:3
exit
hour:4
exit
hour:5
exit
hour:6
exit
hour:7
exit
hour:8
exit
hour:9
exit
hour:10
exit
hour:11
exit
hour:12
enter
hour:13
enter
hour:14
enter
hour:15
enter
hour:16
exit
hour:17
exit
hour:18
exit
hour:19
exit
hour:20
exit
hour:21
exit
hour:22
exit
hour:23
exit
$

if [ $hour -ge 3 ] && ! ( [ $hour -ge 12 ] && [ $hour -le 15 ] ); then

hour=$1 
echo "hour:$hour" 
case $hour in
1|2|12|13|14|15)    # Not allowed
        exit
        ;;
esac

1|2|1[2-5])
...
;;