Re: suggestion to avoid erroneous lines in findmnt/lslocks/...

["Pádraig Brady" <P@draigBrady.com>]

On 08/07/2012 09:09 AM, Karel Zak wrote:
> On Mon, Aug 06, 2012 at 03:44:21PM +0100, Pádraig Brady wrote:
>> I did a quick test...
> 
>  Thanks, I'll use it in regression tests ;-) (I was busy yesterday to
>  write any reg.tests.)
> 
>> TARGET                 SOURCE     FSTYPE OPTIONS
>> /home/padraig/tst/ascii /dev/loop1 ext2   rw,relatime,seclabel,errors=continue
>> /home/padraig/tst/ascii
>> TARGET                       SOURCE     FSTYPE OPTIONS
>> /home/padraig/tst/co\x0atrol /dev/loop1 ext2   rw,relatime,seclabel,errors=continue
>> /home/padraig/tst/co\x0atrol
>> TARGET                       SOURCE     FSTYPE OPTIONS
>> /home/padraig/tst/back\slash /dev/loop1 ext2   rw,relatime,seclabel,errors=continue
>> /home/padraig/tst/back\slash
>> TARGET                       SOURCE     FSTYPE OPTIONS
>> /home/padraig/tst/es\x63aped /dev/loop1 ext2   rw,relatime,seclabel,errors=continue
>> /home/padraig/tst/es\x5cx63aped
>> TARGET SOURCE     FSTYPE OPTIONS
>>
>>        /dev/loop1 ext2   rw,relatime,seclabel,errors=continue
>> /home/padraig/tst/non\xfffffffatf8
>> TARGET                         SOURCE     FSTYPE OPTIONS
>> /home/padraig/tst/日一二三四五六 /dev/loop1 ext2   rw,relatime,seclabel,errors=continue
>> /home/padraig/tst/\xffffffe6\xffffff97...
>>
>> So two questions.
>>
>> 1. Should the back\slash case be back\x5cslash in both cases?
> 
>  back\slash is not \x<xdigit> sequence, so escape is unnecessary
> 
>  Note that \\server\path is pretty common for cifs and use \x5c
>  for all '\' will make the findmnt output unreadable in many cases.
>  IMHO is better to be "smart" and use escape sequences only when it's
>  really necessary.

Better for humans, but awkward for scripts to parse.
What I was thinking was perhaps --raw or -P would
do unconditional escaping of '\' so unescaping can be
done with just `printf %b`?

With the conditional escaping you'd have to do something like:

unmangle() {
  printf '%b' $(
    sed '
      s/\\\([^x]\)/\\x5c\1/g;
      s/\\\(x[^0-9a-f]\)/\\x5c\1/g;
      s/\\\(x[0-9a-f][^0-9a-f]\)/\\x5c\1/g;
    '
  )
}

> 
>> 2. The nonútf8 one produces an errant new line.
>> Also in this case could you fall back to using \x escapes for the whole string?
> 
>  Yeah, nonútf8 output seems strange, I'll fix it.
> 
> 
>  I'll also update findmnt (and others) man pages to explain when and
>  how we use \x escapes. Is there any elegant way how to convert \x
>  sequences back to the native strings in shell? Maybe we can add some
>  hint to the man pages too.

cheers,
Pádraig.