Bourne shell script need help please ?

dezithug · #1 (**permalink**) 10-18-2001

i have this assignment.. and i mad this script but there is something wrong with it.. if anyone can tell me.. watz going on... i would appreciate it.. tHnX in advance..

Code:

count=1
val=$2
op=$1
ans=0
if [ $op = "-e" -o $op = "-o" ]
then
        if [ $op = "-e" ]
        then
                while [ $count -le $val ]
                do
                        ans=`expr $count % 2`
                        if [ $ans -eq 0 ]
                        then
                        echo "$count \c "
                        count=`expr $count + 1`
                        fi
                done
        elif [ $op = "-o" ]
        then
                while [ $count -le $val ]
                do
                        ans=`expr $count % 2`
                        if [ $ans -ne 0 ]   
                        then
                        echo "$count \c "
                        count=`expr $count + 1`
                        fi
                done
        fi
else
        while [ $count -le $val ]
        do
                echo "$count \c "
                count=`expr $count + 1`
        done
fi

ThnX again

added code tags for readability --oombera

LivinFree · #2 (**permalink**) 10-19-2001

One thing I did notice is that if you are using Linux, you should change the echo statements to "echo -e". That will let the \c operators work.

What exactly are you trying to do here? I'm having a tough time reading the script (look, it's late, and I've been plugging some overtime on top of my normally long days...). It looks like you could use some comments...

Have you leaned how to use "case" yet? If so, you may look into using that - you could cut a lot of the confusing "if" statements out of there...

dezithug · #3 (**permalink**) 10-19-2001

well see.. i 'm using SCO UNIX .. nd.. everything works.. fine.. except in the loop something iz wrong.. when i try to run it.. it will juss keep on going... for some reason... nd its soo confusing..

we haven't learnt CASE yet.. i know it would be easier.. but.. i donno how to use CASE..

if yoiu still can think of something.. dat would be gr8

ThnX

LivinFree · #4 (**permalink**) 10-23-2001

Well, first off, it helped me a lot to look at the code with indents in it:

Code:

#!/bin/ksh
count=1 
val=$2 
op=$1 
ans=0 
if [ $op = "-e" -o $op = "-o" ] 
then 
     if [ $op = "-e" ] 
     then 
     while [ $count -le $val ] 
     do 
     ans=`expr $count % 2` 
          if [ $ans -eq 0 ] 
          then 
          echo "$count \c " 
          count=`expr $count + 1` 
          fi 
     done 
     elif [ $op = "-o" ] 
     then 
     while [ $count -le $val ] 
     do 
     ans=`expr $count % 2` 
          if [ $ans -ne 0 ] 
          then 
          echo "$count \c " 
          count=`expr $count + 1` 
          fi 
     done 
     fi 
else 
while [ $count -le $val ] 
do 
echo "$count \c " 
count=`expr $count + 1` 
done 
fi

Now, the first thing I usually try when trying to figureout what my script is doing is to add a "set -x" line at the top of the script. That will echo out each step the shell is performing, so you can see what's going on...

So, The way I ran the script, (I'll give an example of what I think I saw trying to use the" -e 4 "option) it got stuck in a loop at:
+ ans=1
+ '[' 1 -eq 0 ']'
+ '[' 1 -le 4 ']'
++ expr 1 % 2
Ok, interesting... let's look at this. So, what the script is doing step by step:

Code:

     if [ $op = "-e" ]                       # This is true in our case
     then 
     while [ $count -le $val ]          # while 1 is less than or equal to 4
     do 
     ans=`expr $count % 2`         # ans = 1 % 2, or ans = 1
          if [ $ans -eq 0 ]                  # if ans (1) = 0, then continue... nope - can't continue
          then 
          echo "$count \c " 
          count=`expr $count + 1` 
          fi                                         # We're done, time to loop while waiting for ans to equal 0

Do you see what you problem is? Hint: $ans will always equal 1 in this case

Here's another (messier, but more info) way of doing it:

Code:

if [ "$op" = "-e" -o "$op" = "-o" ]
echo " if [ $op = -e -o $op = -o ]"
        then
echo "     then"
        if [ "$op" = "-e" ]
echo "     if [ $op = -e ] "
        then
echo "     then"
        while [ "$count" -le "$val" ]
echo "     while [ $count -le $val ] "
        do
echo "     do"
        ans=`expr $count % 2`
echo "     ans=`expr $count % 2` "
                if [ "$ans" -eq "0" ]
echo "          if [ $ans -eq 0 ] "
                then
echo "          then"
                echo -e "$count \c "
echo "          echo -e $count \c"
                count=`expr $count + 1`
echo "          count=`expr $count + 1`"

This way, you can watch your script in action... It almost looks as if it doesn't know when to exit, right?

You may need a little re-designing, but I think you're pretty much on the right track

(Ooh, and I appologize, I changed some of the "echo"'s to "echo -e"'s, since I was looking at this on a Linux system...

Does this help any?

dezithug · #5 (**permalink**) 10-24-2001

see.. i still donno watz.. wrong.. but.. wat now i'm trin to do iz.. break da program in to lil programz.. and.. trin only -e option.. only for that.. and forget about other options.. hope that will help lol.. but.. thnX nwyz.. i tried.. your code.. but still didnt get.. wat happend.. i know its.. the modulus.. thing screwed up..
ahh.. lol.. i've been workin on this for like 3 weekz.. now.. lol. and its due on nov. 8th.. i have.. some more time..

thnx.. again though.. i appreciate it

dezithug · #6 (**permalink**) 10-24-2001

i finally got it.. to work whoooooooooooooooohooooooooooooooooooooooooooo.. lol.. damn.. dat took me.. long nuff. ..lol.. such a simple program. nd took me.. bout 3 weekz.. damn..

nwy..z. thNx for your help bro.. i appreciate it... very much..

Pz out!!

ThNx Again !!

LivinFree · #7 (**permalink**) 10-24-2001

Right on! Can you post your solution to it for us to see?

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