[libvirt] [PATCH] [TCK] Convert scripts to also run with dash

[Stefan Berger]

On 11/15/2010 02:24 PM, Eric Blake wrote:
> On 11/15/2010 12:08 PM, Stefan Berger wrote:
>> On 11/15/2010 01:50 PM, Eric Blake wrote:
>>> On 11/15/2010 11:24 AM, Stefan Berger wrote:
>>>> I tried this now and converted all \\ to \. I still get the same problem
>>>> here with dash using 'read -r line' now. The same problem exists with
>>>>
>>>> echo "\1"
>>>>
>>>> or
>>>>
>>>> echo '\1'
>>> Ah - the plot thickens, and the light bulb goes on for me.  It's not
>>> just a problem with read, but also with your use of 'echo' to try and
>>> replay a just-read string.  'echo' and '\' don't mix.  You have to use
>>> printf for any chance of portability.
>>>
>>> printf %s\\n "\1"
>>> printf %s\\n '\1'
>> I am surprised that dash doesn't take the opportunity to already extend
>> "\1" or '\1' to char(1) in these cases.  A mystery... :-)
> As a shell argument in isolation, "\1" is undefined in POSIX, but "\\1"
> and '\1' are both the two-character strings for \ and 1.
>
> Then, add printf or echo into the mix.  echo is required to do further
> interpolation of some \ sequences (although not all shells enforce this
> by default), but not all sequences.  For echo, dash does some
> non-required interpolations that bash in xpg_echo mode does not do; but
> for printf, both bash and dash provide non-required interpolations.
> Printf is only required to do \ interpolation of its first argument, and
> of any subsequent arguments that line up with %b in the first argument
> (and what's worse, the interpolations required of the two positions of
> printf arguments are different).
>
> Therefore:
>
> echo '\1' =>  undefined by POSIX (bash with xpg_echo outputs \1, bash in
> normal mode outputs \1, dash outputs char(1))
> echo '\\1' =>  defined by POSIX, but not portable (bash with xpg_echo
> outputs \1, bash in normal mode outputs \\1, dash outputs \1)
> echo "\1" =>  doubly undefined by POSIX
> echo "\\1" =>  same problem as echo '\1'
> echo '\01' =>  defined by POSIX, but not portable (bash with xpg_echo
> outputs char(1), bash in normal mode outputs \01, dash outputs char(1))
> printf %s\\n '\1' =>  well-defined as \1 everywhere
> printf %s\\n "\1" =>  undefined by POSIX, although it tends to portably
> output \1
> printf %s\\n "\\1" =>  well-defined as \1 everywhere
> printf '\1' =>  well-defined as char(1) everywhere
> printf %b '\1' =>  undefined by POSIX, although it tends to portably
> output char(1)
> printf %b '\01' =>  well-defined as char(1) everywhere
> printf %b "\1" =>  undefined by POSIX, although it tends to portably
> output char(1)
>
I knew I was operating right on the edge of the POSIX standard when I 
started this script cleanup...  :-)

    Stefan