Re: for loop 'bad math expression'

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Sun, Feb 4, 2024 at 12:49 PM Lawrence Velázquez <larryv@xxxxxxx> wrote:
>
> I'm not sure if the zsh manual spells this behavior out explicitly,
> but bash and ksh share it.

"Arithmetic Evaluation" says (pretty far down after the discussion of
operators):
===
Named parameters and subscripted arrays can be referenced by name within
an arithmetic expression without using the parameter expansion syntax.
For example,
     ((val2 = val1 * 2))
assigns twice the value of $val1 to the parameter named val2.

=(and later)=

Scalar variables can hold integer or floating point values at different
times; there is no memory of the numeric type in this case.

If a variable is first assigned in a numeric context without previously
being declared, it will be implicitly typed as integer or float and
retain that type either until the type is explicitly changed or until
the end of the scope.  This can have unforeseen consequences.
===

It doesn't explicitly say how "the value of $val1" is determined, but
if it were expanded with $val1 you'd get the whole text string which
would then be interpreted as arithmetic, so expanding without the $
works the same.