Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!nuzba.szn.dk!pnx.dk!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: Rainer Weikusat <rweikusat@mssgmbh.com>
Newsgroups: comp.unix.shell,comp.unix.programmer,comp.programming.contests
Subject: Re: The First Pure Shell Contest (PUSH): relativepath
Date: Mon, 22 Aug 2011 21:15:03 +0100
Lines: 167
Message-ID: <87ty99kxtk.fsf@sapphire.mobileactivedefense.com>
References: <9b7kg7F3njU1@mid.individual.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: individual.net P5IxWrtYP5EYpbEZS/SZcwycLfBfQs12olE39ngSWWm78w8MM=
Cancel-Lock: sha1:a3z7GzOzlEqdR8ZxsqQcWej/J8o= sha1:be20yRa3cNZfvE6DsQw2HQxMsc0=
User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux)
Xref: x330-a1.tempe.blueboxinc.net comp.unix.shell:1792 comp.unix.programmer:1178 comp.programming.contests:25

Jens Schweikhardt <schweikh@schweikhardt.net> writes:
>     The First Pure Shell Contest (PUSH)
>
>               == Motivation ==
>
> The shell is not known for powerful string processing.

For sake of completeness.

NB: I do not claim that this would be good for anything except that
it survives the unit_test() function. Also, it is not supposed to be
'competitive'.

-----------------------------
# Name

split()
{
    eval "case \"\$$1\" in
	?*/*)
	    $3=\${$1#/}
	    $2=\${$3%%/*}
	    $3=\${$3#*/}

	    return 0
	    ;;
	    
	/*)
	    $3=\${$1#/}
	    ;;
	    
         *)
	    $3=\"\$$1\"
    esac
	    
    $2=''"
}

error()
{
    echo "<$1> not absolute or canonical"
}    

valid()
{
    rc=1
    test "${1#/}" != "$1" && {
	rc=''
	case "$1" in
	    *//*)
		rc=1
		;;

	    *?/)
		rc=1
		;;

	    */./*)
		rc=1
		;;
		
	    */../*)
		rc=1
		;;
		
	    */..)
		rc=1
		;;

	    */.)
		rc=1
		;;
	esac
    }

    test -z "$rc" && return 0

    result=`error "$1"`
    return 1
}

one_up()
{
    result="../$result"
}

one_down()
{
    eval "result=\"\$result\$$1/\""
}

walk()
{
    w="$1"
    split w fw rw
    while test -n "$fw";
    do
	$2 fw

	w="$rw"
	split w fw rw
    done

    $2 rw
    return 0
}

relativepath()
{		
    d0="$1"
    valid "$d0" || return 1
    
    d1="$2"
    valid "$d1" || return 1

    split d0 fa ra
    split d1 fb rb
    
    while test -n "$fa" -a "$fa" = "$fb";
    do
	a="$ra"
	split a fa ra

	b="$rb"
	split b fb rb
    done

    result=''
    if test -n "$fa";
    then
	a="$ra"
	
	if test -n "$fb" -o "$fa" != "$rb"
	then
	    a="/$fa/$a"
	    
	    test -n "$rb" && {
		b="$rb"
		test -n "$fb" && b="/$fb/$b"
		walk "$b" one_down
	    }
	fi

	walk "$a" one_up
    elif test -n "$fb";
    then
	b="$rb"
	if test "$ra" != "$fb";
	then
	    b="/$fb/$b"
	    test -n "$ra" && one_up
	fi
	
	walk "$b" one_down
    else
	test "$ra" = "$rb" && {
	    result=.
	    return 0
	}

	result="$rb"
	test "$d0" != / && result="../$result"
   fi

   result="${result%/}" 
   return 0
}