Homework & Coursework Questions

1. The problem statement, all variables and given/known data:
So I have to write a Bourne script that will add two numbers, taking only two arguments and informs the user when it is used incorrectly.

2. Relevant commands, code, scripts, algorithms:

It has to be done in sh. I think overall, it is a pretty basic script.

3. The attempts at a solution (include all code and scripts):

#!/bin/sh

addnumbers()
{ if [$3 = ""]; then
sum = 'expr $1 + $2'
echo $sum
else
echo "Please only enter two arguments."
fi
}

done

4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):
University of Notre Dame, IN, US, Freeland, CSE30189 Basic Unix for Engineers


What I am having trouble with is testing it out. From what I understand, I should have the file in my directory, chmod to like 755 or something, then just type in the name of the file. However, I was wondering how I could pass arguments into it to actually run it through the function. Also, I was unsure as to how I could make sure it was only two values, so I just made it so that if $3 was anything other than blank, it would just exit it.

Thanks for any advice you guys can give!

Code:

#!/bin/sh

addnumbers()
{ if [ $# -eq 2 ]; then          
#in this line space after "[" and before "]" are important! $# stand for the number of arguments
sum=`expr $1 + $2`            
#in this line Do not use space befor and after "=" and use back quote instead of single quote
#not that inside the function, $1 and $2 stand for the parameter of your function !!!
echo $sum
else
echo "Please only enter two arguments."
fi
}

# if you define a function and then never call it, then your script will never give you an output so in the following line, we are calling the function
addnumbers $1 $2           
#in this line, $1 and $2 stand for the parameter of your script !!! 

Code:

$ cat myfile
#!/bin/sh

addnumbers()
{ if [ $# -eq 2 ]; then
sum=`expr $1 + $2`
echo $sum
else
echo "Please only enter two arguments."
fi
}
addnumbers $1 $2
$ sh myfile 4 5
9
$

if you run it $ ./myfile 3 4, you will need it to have the execution right

but if you run it $ sh myfile 3 4 , then the read permission are sufficient since sh has the execute permissions to run it.

Thanks, that really helped. I had to modify it to add $3 to make it have the "else" part, but then it worked! Also, didn't know that you shouldn't have 'done' at the end too, but I just took that out.

Thanks for your help, I really appreciate it.

Quick question though: what does the -eq in the

{ if [ $# -eq 2 ]; then

mean? I know that we want to see if there are any more than 2 arguments. What does -eq do for that?

done is used to end a loop :

Code:

while [ condition ... ]
do
cmd1
cmd2
...
done

Code:

for i in $LIST
do
cmd1
cmd2
...
done