Re: while clause with two conditions does not execute when continue is used

[Freek de Kruijf]

Op donderdag 22 oktober 2020 04:11:10 CEST schreef Dale R. Worley:
> rrd@beelaertsict.nl writes:
> > #!/bin/bash
> > # test error in while clause
> > #
> > set -x
> > up () {
> > 
> >     i=$(($i+1))
> >     [ $i -eq 5 ] && j=$(($j+1)) && i=0
> > 
> > }
> > i=0
> > j=0
> > # while loop should end when i=4 and j=2
> > while [ $i -ne 4 -o $j -ne 2 ]
> > do
> > 
> >     if [ $i -eq 3 ]
> >     then
> >     
> >     up && continue
> >     
> >     fi
> >     echo i=$i j=$j
> >     up
> > 
> > done
> 
> It would have helped if your example wasn't so very complicated.  I
> suspect that you are expecting some of the "&&" to act like ";" that is,
> the command following will always be executed.  If you expect that, you
> should write the code to make that explicit.  In addition, you didn't
> place echo's in places that would be quite informative, especially
> around the "continue" and at the bottom of the loop.
> 
> If I add some echo's like this:
> 
>     #!/bin/bash
>     # test error in while clause
>     #
>     set -x
>     up () {
>         i=$(($i+1))
>         [ $i -eq 5 ] && j=$(($j+1)) && i=0
>     }
>     i=0
>     j=0
>     # while loop should end when i=4 and j=2
>     while [ $i -ne 4 -o $j -ne 2 ]
>     do
>         echo Testing i == 3
>         if [ $i -eq 3 ]
>         then
>             echo Continuing
>             up && continue
>             echo continue not executed
>         fi
>         echo i=$i j=$j
>         up
>         echo At bottom i=$i j=$j
>     done
> 
> and then run it, the relevant segment of the output is
> 
>     + echo At bottom i=3 j=2
>     At bottom i=3 j=2
>     + '[' 3 -ne 4 -o 2 -ne 2 ']'
>     + echo Testing i == 3
>     Testing i == 3
>     + '[' 3 -eq 3 ']'
>     + echo Continuing
>     Continuing
>     + up
>     + i=4
>     + '[' 4 -eq 5 ']'
>     + echo continue not executed
>     continue not executed
>     + echo i=4 j=2
>     i=4 j=2
>     + up
>     + i=5
>     + '[' 5 -eq 5 ']'
>     + j=3
>     + i=0
>     + echo At bottom i=0 j=3
>     At bottom i=0 j=3
> 
> This makes it clear what is happening:  when i == 3, the "if" is entered
> and the "up" is executed.  But the "up" returns status 1, and so the
> "continue" is not executed.  Execution continues in the block to the
> second "up", which increments i and then rolls over to increment j.  The
> exit condition is never met.
> 
> Dale

Indeed the && before continue should have acted as ; I did not realize up 
could return a status 1 and not execute continue. Inserting "return 0" at the 
end of up solves the problem.

Many thanks for the lesson.

-- 
fr.gr.

Freek de Kruijf