Check assignment of SAGE_ROOT in $SAGE_ROOT/sage

[jdemeyer]

The top-level Sage script doesn't check the value of SAGE_ROOT if it was set from the outside. Example:

$ SAGE_ROOT=does_not_exist ./sage
./sage: line 118: cd: does_not_exist: No such file or directory
./sage: line 122: /spkg/bin/sage: No such file or directory

After:

$ SAGE_ROOT=does_not_exist ./sage
./sage: line 118: cd: does_not_exist: No such file or directory
./sage: cannot determine SAGE_ROOT directory

The new top-level script can now also be used together with sage-4.x:

$ SAGE_ROOT=/usr/local/src/sage-4.8.alpha6 /usr/local/src/sage-5.0.beta1/sage
----------------------------------------------------------------------
| Sage Version 4.8.alpha6, Release Date: 2012-01-01                  |
| Type notebook() for the GUI, and license() for information.        |
----------------------------------------------------------------------
**********************************************************************
*                                                                    *
* Warning: this is a prerelease version, and it may be unstable.     *
*                                                                    *
**********************************************************************
sage:

apply attachment: 12522_check_sage_root.patch to SAGE_ROOT.

Component: scripts

Author: Jeroen Demeyer

Reviewer: Volker Braun

Merged: sage-5.0.beta5

Issue created by migration from https://trac.sagemath.org/ticket/12522

[jdemeyer]

comment:2

Attachment: 12522_check_sage_root.patch.gz

[vbraun]

comment:3

More error checking can't hurt ;-)

[vbraun]

Reviewer: Volker Braun

[jdemeyer]

Merged: sage-5.0.beta5