ash bug ?

[Juergen Hennerich]

walter harms schrieb:
> hi list,
> riaz and i are working on documenting ash. so i tried to run the bash test scripts on ash.
> and one place ash breaks where sh works. bug or feature ?
The (( )) (ARITHMETIC EVALUATION) is a ksh (Korn SHELL) feature which is 
  supported by bash but not by ash. In contrast to the arithmetic 
expansion ("$(( ))") which is supported by ash the arithmetic evaluation 
gives back either 0 or 1 as result of the evaluation. Also the 
arithmetic expansion works different with ash which requires that 
variables inside the expansion are prefixed with $ in contrast to bash. 
(I just saw, that it is supported (arithmetic expansion without $) in 
the busybox ash, The normal ash which is installed on most Linux systems 
has a different behavior)

> ash is running endless because it does not find 'x'
> 
That is completely logical.
> x=3
> until (( x == 4 )) ; do
>         x=4
> done
> 
> note:
> 
> removing the spaces solves the problem.
> 
No it does not!
Try: x=1 ; until (( x==4 )) ; do echo bla $x ; x=$(($x+1)) ; done
You'll see, that it does not, what you want it to do.

Instead you should either use:
x=1 ; until [ $x -eq 4 ] ; do echo bla $x ; x=$(($x+1)) ; done
or
x=1 ; until ( expr $x == 4 >/dev/null ) ; do echo bla $x ; x=$(($x+1)) ; 
done
or
x=1 ; until let x==4  ; do echo bla $x ; x=$(($x+1)) ;

Or course the functionality could easily implemented in busybox ash, 
since the functionality is already there: ((x)) <-> let x .


Juergen

> re,
>  wh
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