Hi Martijn, > On Jan 29, 2017, at 4:13 PM, Martijn Dekker <mart...@inlv.org> wrote: > > Op 19-01-17 om 21:06 schreef Michael Greenberg: >> unset x ; echo $((x+=2)) >> >> Running bash on this program echoes the number 2 to standard out and sets x >> to 2. Running dash (git HEAD/release 0.5.9.1) yields an error: >> >> src/dash: 1: Illegal number: > > Yes, looks like a dash-specific bug. The related shells Busybox ash and > FreeBSD /bin/sh act like POSIX says they should.
Great! Please pardon my naivete, but is there anything else I can or should do to see that this bug patch gets accepted and applied? >> The standard is a little bit unclear about what to do for variables that are >> set to null (or non-numeric values). I’d interpret the standard as >> defaulting for unset variables, having null and other non-numeric strings >> cause some kind of error. bash, as usual, goes well beyond what the standard >> indicates: any non-numerical value is defaulted to 0. So: >> >> x="" ; echo $((x+=2)) >> >> x=“yo” ; echo $((x+=2)) >> >> both yield 2! If you ask me, that’s a bridge too far—and asking for bugs. > > That's recursive arithmetic expression parsing in bash, ksh and zsh; if > the value of a variable is an arithmetic expression (including simply > another variable name, such as "yo") this is evaluated, which in this > case means the value of "x" is taken as the value of "yo" which is taken > as zero. That behaviour is not specified by POSIX, of course. Right. I only mentioned it because I—as I think we both agree—this behavior is underspecified and probably good as-is. :) Cheers, Michael
