pathos script

[Alan Watson <alan@oldp.astro.wisc.edu>]

About a year ago John Mackin posted a pathos script.  The idea was that
you could use it in a front-end version of a standard command to invoke
the a command further down the path.  

John noted that there was a problem if if a script got exec-ed with a
relative pathname.  I think I've come up with a way to get around
this.  All of those pwds can take a little while, but the additional
bullet-proofing seems worthwhile to me as it doesn't cause much of a
burden in the normal case.

I prefer to use:

	exec `{ pathos $0 } $*

as it alleviates the need to protect variables.  On failure, pathos
prints an error message on stderr and false on stdout, which I think is
quite a nice way to deal with that situation.

BTW, John, why did you choose the name `pathos'?

Alan.

#! /tmp/alan/bin/rc --

if ( ! ~ $#* 1 ) {
   echo >[2=1] usage: pathos path
   echo false
   exit 1
}

thisdir  = `{ dirname  $1 } 
thisbase = `{ basename $1 }

# shift $path past $thisdir
* = $path
if ( ~ $thisdir $* ) {
   while ( ! ~ $thisdir $1 ) {
      shift
   }
} else {
   thisdir = `{ builtin cd $thisdir ; builtin pwd }
   while ( ! ~ $#* 0 && ! ~ $thisdir `{ builtin cd $1 ; builtin pwd } ) {
      shift
   }
   if ( ~ $#* 0 ) {
      echo >[1=2] pathos: unable to find $thisdir in path
      echo false
      exit 1
   }
}
shift

# look for executable $thisbase in remainder of $path
# if whatis succeeds, it prints the path on stdout for us
while ( ! ~ $#* 0 ) {
   if ( whatis $1/$thisbase >[2=] ) {
      exit 0
   }
   shift
}

echo >[1=2] pathos: unable to find $thisbase
echo false
exit 1

# end-of-file