On Thu, Aug 18, 2011 at 9:02 PM, Jeroen Demeyer <jdeme...@cage.ugent.be>wrote:
> Hello sage-devel,
>
> Can somebody explain the rationale for the following lines in
> $SAGE_ROOT/sage:
> if [ "$SAGE_ROOT" = "....." ]; then
> SAGE_ROOT=`readlink -n "$0" 2> /dev/null` || \
> SAGE_ROOT=`realpath "$0" 2> /dev/null` || \
> SAGE_ROOT="$0"
>
> I think the following would work equally well:
> if [ "$SAGE_ROOT" = "....." ]; then
> SAGE_ROOT="$0"
>
>
>
I assume those lines are supposed to try to determine the location of the
sage install when sage is not run from the directory where is it install. I
think that they work when the sage executable is called directly, and your
proposal would probably work equally well in that case, but they seem broken
in other cases. I generally link sage-(release number) to ~/sage, and then I
link ~/bin/sage to ~/sage/sage, and I've always had to set SAGE_ROOT
explicitly. Are those lines supposed to be there so that I don't have to set
the path explicitly?
I think that in my case something like the following would work:
cd "${0%/*}"
SAGE_RELATIVE_PATH=`readlink -n "$0"`
cd "${SAGE_RELATIVE_PATH%/}"
SAGE_ROOT=`pwd`
> Note that this is not needed to get an absolute (rather than relative)
> path, since below there is
> # Make root absolute:
> cd "$SAGE_ROOT"
> SAGE_ROOT=`pwd`
>
> If we really want to resolve symbolic links, we could replace `pwd` by
> `pwd -P` (physical path).
>
>
> In any case, "readlink -n" certainly does NOT do what is intended and
> should be removed (#11707):
> - It only works when `$0` (the sage executable itself) is a symbolic
> link, it does not work when some other component in the path is a
> symbolic link.
> - If the sage executable is a symbolic link, then `readlink -n` returns
> the link itself, not the canonicalized name. Example: if
> `/usr/local/sage-4.7.1/sage` is a symbolic link to `sagefoo`, then
> `SAGE_ROOT` would become `sagefoo` when `'/usr/local/sage-4.7.1/sagefoo`
> is intended.
>
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