optimize if block : shell script


 
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# 1  
MySQL optimize if block : shell script

Hi,

I need a shell script to determine if a no. is either even, greater than 4, less than 8
SHELL : ksh
OS : RHEL 6
this is the if block of the script

Code:
 
mod=`expr $num % 2`
if [ "$mod" -eq 0 ] || [ "$num" -gt 4 ] || [ "$num" -le 8 ]
then
      echo "No. is either even or greater than 4 or less than 8"
fi

this code works fine,
however i want to find out which test block(s) of the conditions in if is having true value and take action on according to the result

for this the if block i have designed is quite cumbersome and not at all optimized pair of if-elif-else blocks,

Code:
 
mod=`expr $num % 2`
flag1=0
flag2=0
if [ "$mod" -eq 0 ] 
then
      echo "No. is even"
      flag1=0
fi
 
if [ "$num" -gt 4 ] && [ "$flag1" -eq 1 ]
then
      echo "No. is even and greater than 4"
      flag2=0
elif [ "$num" -gt 4 ]
then
      echo "No. is greater than 4"
      flag2=0
fi
 
if [ "$num" -lt 8 ] && [ "$flag2" -eq 0 ]
then
      echo "No. is even greater than 4 and less than 8"
elif [ "$num" -lt 8 ] && [ "$flag1" -eq 0 ]
then
      echo "No. is even and less than 8"
else
      echo "No. is less than 8"
fi

can anyone suggest any way to optimize this ?

Thanks
# 2  
Your logic has problems. I preserved the bad logic in this code
Code:
#!/bin/ksh
num=$1
mod=`expr $num % 2` 
result=0                                            
[ $mod -eq 0 ] && result=1 
[[ $result -eq 0 &&  $num -gt 4  ]] && result=2 
[[ $result -eq 0 &&  $num -lt 8  ]] && result=3     
if [ $result -gt 0 ] 
then                                     
      echo "No. is either even or greater than 4 or less than 8"
      echo "result is $result"
fi

If you test for > 4 and set result to 2 you never get a result for less than 8.
Did you mean > 4 and <= 8? rather than just > 4?

You can change the code to fit your requirements.
# 3  
You could also use the binary numbers to represent the results of your tests. Think permissions on UNIX:
Code:
7 == rwx = 100 + 010 +001

Just keep prepending 0 or 1 to the flag:
Code:
#!/bin/ksh

num=$1

cat <<EOF

111
││└── is even
│└─── is > 4 
└──── is <= 8

EOF

[[ $(($num % 2)) -eq 0 ]] && a=1 || a=0
[[ $num -gt 4 ]] && a=1$a || a=0$a
[[ $num -le 8 ]] && a=1$a || a=0$a

echo $a

Code:
$ ./test.ksh 7
111
││└── is even
│└─── is > 4 
└──── is <= 8

110

 

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