Confusion about FOR LOOP syntax between Bourne and BASH shell. Please see.

Shell Programming and Scripting
1 
for (( i=1; i<=3; i++ )); do
for (( j=1; j<=3; j++ )); do
for (( k=1; k<=3; k++ )); do
echo $i$j$k
done
done
done

Will the above code work on a BOURNE shell?

As far as my understanding is, if I am writing the above code in a file..say lol.sh and then running it through the terminal using the command

sh lol.sh

then I am using the Bourne Shell. Am I right with this concept?

If yes, then the above code won't run (as I tried to run it) BUT it runs when i run it as...

bash lol.sh

So my question is that :

  1. Am I correct that sh lol.sh will run it using bourne shell ?

  2. And can for loop be written in the way it's written in the code above in the bourne shell or

for i in 1 2 3

is the only possible syntax of for loop in the bourne shell?

2

No, that will not work in a generic Bourne shell. Generic Bourne shells don't even have math, you have to use the expr external.

The latter is what should be used for a generic bourne shell, yes. Or something like

I=1
while [ $I -le 3 ]
do
        I=`expr $I + 1`
done
3

If bourne shells doesn't have math then how am I able to execute statements like

 var=$(($1-1))

And is it possible to find x to the power of y using expr function (or in any possible way in bourne shell except "for" loop) where x and y are two numbers read from the terminal?

4

By using the expr external, like I said.

VAR=`expr $VAR - 1`

Certainly, by running a loop which multiplies x against itself y times.

Is this homework?

5

Thank you for your time but if you would read my last post carefully and not skim over it... you'd see that I said "except for loop" which implies that I already know how to do it with a for loop but I was asking you for some other method "if it exits".

Second thing, I KNOW that it can be done by the expr command but I asked you that WHY I am getting away with using a command like $((...mathematical expression...)) if I am working in the bourne shell WHICH implies that I ALREADY understood that expr can be used.
I do understand if "...am i able to..." couldn't really pass my message along clearly but I think "....except for loop...." was mentioned pretty neatly.

Again, thank you for your time and effort but kindly re read the post before tagging my genuine problem as "homework".

6

On some systems Bourne shell (sh) is actually Bash (bash).
Compare the sizes/links of /usr/bin/sh and /usr/bin/bash

As far as power is concerned:

$ nawk 'BEGIN{ print 2^3}'
8
7

A simple "no" would have sufficed. I didn't "tag" your post as homework, I asked.

Most of the time I ask, the answer is "yes". Your question looked contrived, as homework frequently is, because calculating X^Y isn't something that makes much sense to do in a shell. If it was homework, I'd have been breaking the rules by giving you an answer. I've been burned several times by blatant cheaters, too.

If I ask someone what their shell is, and they tell me "Bourne", I ask "which Bourne" because "bourne" means it supports at least the Bourne shell features, not that it's the One and Only True Original Bourne Shell. Some systems -- particularly Linux ones -- use Bash as their Bourne shell, many others use KSH, and a few poor Solaris folks are stuck using an actual ancient pre-POSIX Bourne shell which hasn't been improved since the dawn of UNIX.

If $(( )) works, you're either in bash or ksh.

I don't know a simple syntax for taking a number to a power in either. If I had to do so in basic Bourne, I'd probably pipe "$x^$y" into bc. If you try and do that in $(( )), it's a bitwise exclusive-or, not x to a power, since $(( )) mostly emulates the C expression syntax, and C has no operator for power.

1 Like
8

Okay.

Thanks again.