gawk substr() problem

[Stepan Kasal]

Hello,
        I've discovered a bug in GNU awk (tried with 3.1.1 and 3.0.4):

substr(str, start, len)

  - POSIX doesn't say what to do if `start' is less or equal to 0.
        I'd say it should be an error.  GNU awk manual says that the null
        string is returned.

when you call substr() in gawk with start <= 0, it behaves as if start
was 0, which differs from the above specification.

$ gawk-3.1.1/gawk 'BEGIN{print substr("abc",-5,2)}'
ab
$

Wouldn't it be best to fix both docs and code and issue an error message
if `start' is <= 0.
It would be particularily helpful for  start == 0  as this indicates that
the programmer has forgotten that awk strings are indexed from 1.

(Willing to make a patch, when the king's ruling is known.  :-)

  - POSIX doesn't say what to do if `len' is negative.
        GNU awk returns the null string.

This is not a bug but a feature request: wouldn't it be better to issue
an error message instead?

Have a nice day,
        Stepan