Bourne Shell Programming help!

radmofopunk · 04-22-2006, 07:03 PM

Quote:

Originally Posted by /bin/bash

You seem to be mainly focusing on expr command so I think you should stick with that. Now to get the values into the script from file1-file3 you should use a command you have already gone over in lab like maybe cat or read. Here is an example using cat with pipe and also file redirection using <.

Code:

#!/bin/bash
while read NAME SCORE;do
echo "NAME = $NAME"
echo "SCORE = $SCORE"
done <file1

#Another way to do it would be
echo "______________"
cat file1|
while read NAME SCORE;do
echo "NAME = $NAME"
echo "SCORE = $SCORE"
done

Now using what you aready know you should be able to add the $SCORE increment $COUNT and finally divide $TOTAL by $COUNT if $COUNT != 0.

This is much more like what we are doing in class, thank you. Here is what I typed in, I still can't figure it out, but I am so much closer:

Code:

#!/bin/sh
sum=0
total=0
count=0
while read NAME SCORE;do
sum=`expr $sum + $SCORE`
count=`expr $count + 1`
done <$1
echo "sum = $sum"
echo "count = $count"
if $count != 0
        then
                echo "average = $sum/$count"
fi

But here is what shows up:

Code:

bash-2.05$ new quiz1
sum = 0
count = 0
./new: 0: not found

So, it isn't adding up the scores or count at all, anyone know why?

paulsm4 · 04-22-2006, 08:13 PM

The "read" doesn't necessarily like end-of-file; "expr" doesn't like null variables - and one or the other could be messing up your other variables.

Please try something like this:

Code:

#set -x
  while read NAME SCORE;do
    if [ ! -z "$NAME" ] && [ ! -z "$SCORE" ]; then
      SUM=`expr $SUM + $SCORE`
      COUNT=`expr $COUNT + 1`
    fi
  done < $1

This "protects" your expr against null values for NAME or SCORE.

PS:
If you uncommented "set -x", you get very useful debug statements.

PPS:
The purpose of quoting "$NAME" and "$STRING" like that was to insure that the "[ ! -z ]" test command gets an empty string ("") instead of nothing at all ( ).

PPS:
A long time and many posts ago, Dive gave you a useful link to a good shell scripting site:
http://www.tldp.org/LDP/abs/html/

Definitely good stuff - and, based on your experience with this assignment, I think you'll get a lot more out of it the next time you look at it. IMHO...

radmofopunk · 04-22-2006, 08:38 PM

Same results, still sum=0 and count=0

It is adding it up correctly, according to the debugging thing, but it resets itself back to 0 for some reason

paulsm4 · 04-22-2006, 10:05 PM

Here's the data set I tested:

Quote:

cat quiz1.txt
Ann 24
James 20
Joseph 22
Melanie 20
Timothy 24

Here's the complete script:

Code:

#!/bin/bash

  # Chk cmd-line args
  if  [ $# -ne 1 ]; then
    echo "USAGE: chk_grades <filename>"
    exit 1
  fi

  SUM=0
  TOTAL=0
  COUNT=0
  SCORE=0

  #set -x
  while read NAME SCORE;do
    if [ ! -z "$NAME" ] && [ ! -z $SCORE ]; then
      SUM=`expr $SUM + $SCORE`
      COUNT=`expr $COUNT + 1`
    fi
  done < $1

  echo "SUM = $SUM"
  echo "COUNT = $COUNT"
  if [ $COUNT -gt 0 ]; then
    AVG=`expr $SUM / $COUNT`
    echo "average = $AVG"
  else
    echo "AVERAGE UNDEFINED!"
  fi

And here's sample output:

Quote:

./grade_quiz.sh quiz1.txt
SUM = 110
COUNT = 5
average = 22

/bin/bash · 04-23-2006, 01:25 AM

Make sure you don't have any extra lines in your quiz file. The extra lines could be causing problems. Here is a way to test it. The output should look like the first example.

$ cat quiz1;echo "end"
Ann 24
James 20
Joseph 22
Melanie 20
Timothy 24
end

$ cat quiz1;echo "end"
Ann 24
James 20
Joseph 22
Melanie 20
Timothy 24

end

If the output looks like the second example then you have extra lines in the quiz1 file and you need to delete them.

paulsm4 · 04-23-2006, 02:18 AM

Hi, /bin/bash -

The "[ ! -z ... ]" check will protect against blank lines (and/or missing data fields). I think the problem radmofopunk ran into was probably at the end of the file - which could occur even if the quiz file didn't appear to have any blank lines.

In any case: the best policy is always to assume that your input data *will* have errors, and protect against it in your code.

IMHO .. pSM

radmofopunk · 04-23-2006, 06:24 PM

Well, I figured it out. It wasn't a problem with the quiz1 having blank lines, here is the final code that works:

Code:

bash-2.05$ cat average
#!/bin/sh
sum=0
count=0
exec <$1
while read line
do
        set $line
        sum=`expr $sum + $2`
        count=`expr $count + 1`
done
echo "sum = $sum"
echo "count = $count"
if [ $count != 0 ]
        then
                echo "average = `expr $sum / $count`"
        else
                echo "average = undefined"
fi

exit 0

paulsm4 · 04-23-2006, 06:45 PM

Cool - excellent work, radmofopunk!

radmofopunk · 04-23-2006, 07:58 PM

Thanks again to everyone, couldn't have done it without you.

cramer · 04-23-2006, 08:53 PM

Nice. that != in the if statement means if $count isn't 0 then divide the sum by the count, and if it is 0 then say undefined right? I am unfamiliar with using !=

radmofopunk · 04-23-2006, 10:09 PM

Yes, != means not equal, so if it isn't 0, then it will divide it, otherwise (or it is 0), it will display undefined.

JrLz · 04-23-2006, 10:53 PM

this is a great lesson

we should take care of blank files, and zero division
sorry radmofopunk, i put the wrong filename in my script
it should be quiz1, not jawab
and when you say (in my script)

Code:

 for x in $(cat quiz1)

you're reading each word (separated by whitespaces)in the file
and when you do math calculation, it abandons the string words

it wasn't a good script, just forget it

/bin/bash · 04-24-2006, 03:13 AM

Quote:

this is a great lesson

we should take care of blank files, and zero division

That script doesn't take care of blank lines or even lines with extra whitespace. And blank files... don't even go there. Try putting an extra space in the data or an extra line at the end or give it a blank file and watch it crash.