Re: expr length "$val" returns the wrong length for values containing NULL (\\0)

[D Gowers <finticemo@gmail.com>]

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Ah, okay. That (commandline arguments not being able to contain NUL)
seems.. a bit anachronistic. But I guess it's never been enough of a
problem to warrant the considerable bother to fix it. Fair enough.

On Thu, Dec 10, 2015 at 2:26 PM, Nikolay Aleksandrovich Pavlov (ZyX) <
kp-pav@yandex.ru> wrote:

>
> 10.12.2015, 04:52, "D Gowers" <finticemo@gmail.com>:
> > Test case:
> >
> > v=$(printf foo\\0bar);expr length "$v";expr length $v
> >
> > alternatively:
> >
> > v=foo$'\0'bar;expr length "$v";expr length $v
> >
> > In zsh, the values returned are 3 and 3.
> > In dash and zsh, the values returned are 6 and 6.
> >
> > Both of those results are wrong, AFAICS (foo$'0'bar is 7 characters
> long).
> > But the zsh result is more severely wrong. I could understand the
> bash/dash
> > result, at least, as 'NULL characters are not counted towards length'.
>
> Both results are *right*. In both cases you ask the length of the string
> and you get it.
>
> In dash (also posh, bash and busybox ash) zero byte is skipped when
> storing. So length of the $v *is* six. You may question whether it is right
> storing without zero byte, but the fact that all four shells have exactly
> the same behaviour makes me think this is part of the POSIX standard. In
> any case non-C strings are not on the list of features of these shells
> unlike zsh (it also internally uses C NUL-terminated strings, but zero
> bytes and some other characters are “metafied” (i.e. escaped) and
> unmetafied when passed to the outer world e.g. by doing `echo $v` to pass
> string to terminal).
>
> As I said in zsh zero byte is stored. But C strings which are the only
> ones that can be arguments to any program are **NUL-terminated**. So what
> you do is passing string "foo" because NUL terminates the string. You
> cannot possibly get the answer you think is right here thus, unless you
> reimplement `expr` as a zsh function.
>
> >
> > In any case, it is easily demonstrated that the string is not 3
> characters
> > long, by running 'echo "$V"' or 'print "$v"' or 'echo ${#v}'
> >
> > `zsh --version` = 'zsh 5.2 (x86_64-unknown-linux-gnu)'
>