Re: for loop 'bad math expression'

[Ray Andrews <rayandrews@eastlink.ca>]

[-- Attachment #1: Type: text/plain, Size: 1578 bytes --]


On 2024-02-03 15:52, Bart Schaefer wrote:
> As Lawrence also suggested, I don't believe that happens.  If a
> parameter is created inside a math expression it will be assigned an
> appropriate numeric type, but the type of an existing scalar is not
> changed.

0 /usr/share/info 0 % var=abc; let var+=2; echo $var

2

... it looks like the shell is simply throwing away 'abc' and starting 
afresh with an integer and then incrementing it. And in the manual:

Note that assignment may implicitly change the attributes of a 
parameter. For example, assigning a number to a variable in arithmetic 
evaluation may change its type to integer or float, and with GLOB_ASSIGN 
assigning a pattern to a variable may change its type to an array.

> Context-awareness doesn't extend that far.  Globbing is already done
> and gone by the time "for" assigns its loop variable, nothing tells
> "for" where the loop values came from, and shell words on a command
> line carry no type information.

Sure.  I'm hardly surprised it wouldn't be practical, it was the most 
speculative sort of question.  And there really is no foul since my 
variable shouldn't have been an integer.  Actually, philosophically I'm 
opposed to most hand-holding anyway.  With experience I'd probably 
instantly detect what was going on there. But when you first bump into 
it, it seems inexplicable.

>
> You might try setopt warn_create_global to detect cases of names "leaking".
>
Never played with that.  Sounds useful.  As always my 'C-brain' tells me 
that indiscipline with variables is intolerable.



[-- Attachment #2: Type: text/html, Size: 2599 bytes --]