Multiple conditionals in a while loop

Shell Programming and Scripting
1

Hi was wonderring about the syntax for the following peice of code:

while [[ $life != 0 || $mask != $word ]] ; do

This is apparently incorrect. I want the loop to continue WHILE $life is not equal to zero or $mask is not equal to $word. Should ONE of these conditions fail to be met, loop should break out. Any ideas?
thanks in advance: Sant

2

Your logic is at fault. You want the loop to continue WHILE $life is not equal to zero AND $mask is not equal to $word.

De Morgan's laws - Wikipedia, the free encyclopedia

3

@OP, in my opinion, this construct is better. You don't have to "clutter" the while loop conditions.

while [True];
do
     if condition1 is true { break }
     if condition2 is true {break } 
     do_something...
done
4

Using "break" violates good programming standards because it breaks the "single-entry single-exit" rule for control structures.

5

looking at a bigger picture, if the programming language one is using doesn't "enforce" that, it doesn't really matter if one follows the "good" programming practice or not.

6

Goto - Wikipedia, the free encyclopedia

7

Structured Programming with Goto Statements

8

Hi.

I'm not so sure about this claim. There is still a single exit at the bottom of the while, and how you get there seems to be the issue here. I would take the meaning of multiple-exit to be that there would be a place to which control is transferred without explicitly traveling through the end of the while, just as multiple-entry would mean entering the body of the while without going through the top of the while. (For precision I suppose we could say the statement immediately after the end of the while instead of the end of the while itself.)

In any case, I tend to lean toward making understanding and maintenance easy, so readability counts for a lot:

I enjoy these Dharma-duels (as long as they don't get out of hand, and I think I will be a grasshopper for long time) ... cheers, drl

9

I figure your right on... fix what you were doing wrong in the loop and learn something rather than jump ship... I was stuck in the same loop problem and your post helped me. its been years since I wrote anything and forgot how the || was evaluated.. as soon as I read your post it all came back .. Thanks... :slight_smile: