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From: Stephane CHAZELAS <stephane_chazelas@yahoo.fr>
Newsgroups: comp.unix.shell,comp.unix.programmer,comp.programming.contests
Subject: Re: The First Pure Shell Contest (PUSH): relativepath
Date: Tue, 23 Aug 2011 21:56:52 +0000 (UTC)
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2011-08-23, 19:52(+01), Rainer Weikusat:
[...]
>>>> The shell is not known for powerful string processing.
>>>
>> [...]
>>>     echo "<$1> not absolute or canonical"
>> [...]
>>>     while test -n "$fa" -a "$fa" = "$fb";
>> [...]
>>> 	if test -n "$fb" -o "$fa" != "$rb"
>> [...]
>>
>> We may want to add those test cases:
>>
>> /=/x         /            0 ../..
>> /            \\\\\\\\     1 <\\\\\\\\> not absolute or canonical
>
> No. You 'might' (actually, you should) want to point out the problem
> with the two statements above, namely,
>
> 	In addition, the string comparison binary primaries '=' and
> 	"!=" shall have a higher precedence than any unary primary.
>
>       http://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html
>
> and maybe even write that the obvious fix is
> to rewrite this as
>
> 	test -n "$fa" && test "$fa" = "$fb"
>
> (and similar for the other case).
[...]

Yes, you're right. But it's repeated so often on cus that
- you can't use echo for arbitrary data portably or reliably
  -> use printf
- the -a and -o binary test operators shouldn't be used, or more
  generally, past 4 arguments to "test"/"[", the behavior is
  unreliable (-> use &&/|| as you pointed out)

that it goes almost without saying.

>> What about:
>>
>> relativepath(){ for i do case $i/ in /|[!/]*|*/./*|*/../*|*?//*|//?*)
>> result="<$i> not absolute or canonical";return 1;esac;done
>> p=${1%/} r= b=${2%/}/;while :;do case $b in "$p"/*)r=$r${b#"$p"/}
>> r=${r%/};result=${r:-.};break;esac;p=${p%/*} r=../$r;done;}
>
> What about
>
> dd if=/dev/urandom bs=1 count=1024 | base64 | fold -b -w 26
>
> ?
>
> Granted, it doesn't solve the problem but its as unintelligible as
> the gibberish above.

You're just jealous because yours is bigger ;-)

-- 
Stephane