Provided by: grass-doc_6.4.3-3_all 
NAME
g.extension - Tool to maintain GRASS extensions in local GRASS installation.
Downloads, installs extensions from GRASS Addons SVN repository into local GRASS
installation or removes installed extensions.
KEYWORDS
general, extensions
SYNOPSIS
g.extension
g.extension help
g.extension [-lsu] [extension=name] [operation=name] svnurl=url [prefix=path]
[--verbose] [--quiet]
Flags:
-l
List available modules in the GRASS Addons SVN repository
-s
Install system-wide (may need system administrator rights)
-u
Install system-wide using sudo
--verbose
Verbose module output
--quiet
Quiet module output
Parameters:
extension=name
Name of extension to install/remove
operation=name
Operation to be performed
Options: add,remove
Default: add
svnurl=url
SVN Addons repository URL
Default: http://svn.osgeo.org/grass/grass-addons/grass6
prefix=path
Prefix where to install extension
Default: $GRASS_ADDON_PATH
DESCRIPTION
g.extension downloads community contributed addon modules from the GRASS-addons Subversion
repository (SVN) and installs them on the local system. These include modules providing
specialist functionality, modules in development and beta testing, newly proposed modules,
experimental modules, and simple helper scripts. There are additional code contributions
in the SVN repository which are either incomplete or complex to install and so not
available through g.extension. The addons repository acts in part as an incubation area,
so the code there may not be as polished and well reviewed as the core GRASS modules, or
it may not even work at all. All code is license-compatible with GRASS and can be used,
shared, and modified under the same Free-software terms. You are both welcome and
encouraged to contribute your own scripts there, and so make them available via
g.extension, if you feel they would be useful to others.
Re-running the script for an installed GRASS addon module re-installs the requested
extension. This is a handy way to apply updates or rebuild compiled modules after
installing a new version of GRASS.
The default action is to install the files into the first directory listed in the
GRASS_ADDON_PATH environment variable. If that has not been set it will default to
~/.grass6/addons/ on UNIX or %APPDATA%\GRASS6\addons on MS Windows. With suitable
administrative permissions you can optionally install directly into the main GRASS program
directory ($GISBASE).
NOTES
The wxGUI contains a graphical extension manager separate to this version of g.extension.
The wxGUI Extension Manager can be found in the Settings menu. While they are generally
interchangable, this help page describes the version of g.extension run from the GRASS
command line. If one method of installing the addon fails you might try again with the
other.
Help and man pages installed with the module will be available through the g.manual
module.
If your GRASS_ADDON_PATH environment variable contains more than one path, the default
action is to use the first directory in the list. Custom user scripts and installed
addons can share the same addons directory.
Note: Bourne shell and Python scripts run within GRASS that use the g.parser module must
be in the system's search PATH, or else g.parser will not be able to find them and
complain about a failure to obtain the module's interface description. As long as the
GRASS_ADDON_PATH environment variable is set before you start GRASS this will be taken
care of automatically at startup.
For users building all of GRASS from source code who have also checked out the GRASS-
addons Subversion repository, an alternate approach is to cd into the addon module's
source directory, then run:
make MODULE_TOPDIR=/path/to/grass/source
UNIX users can set up an alias in their ~/.bash_aliases file:
alias gmake643='make MODULE_TOPDIR=/path/to/grass643/source'
Users with GRASS installed from a GNU/Linux package can build without the full GRASS
source code installed, but they will need the associated grass-dev and grass-doc packages
installed.
Upgrading the GRASS version and users with multiple versions of GRASS installed on the
same system require special care when dealing with compiled addon modules (those written
in C and C++ and linking to the GRASS C libraries). If you try to run a compiled C addon
module which was built using a different version of GRASS, you will get an error that the
module can not find the shared GIS libraries of the other version, or if it can find them
it will still check the internal versions and exit with an error if they do not match. In
these cases you can simply re-run g.extension to rebuild the module and solve the problem.
You can typically share a single GRASS_ADDON_PATH directory for Bourne shell scripts and
Python addon modules written for any version of GRASS 6. Since your Addon modules and
scripts will typically be in your user's home directory and thus persist even when GRASS
is upgraded or reinstalled, some notes on compatibility:
Forward compatibility: Any script written for GRASS 6.0 or newer should
work without changes with any newer version of GRASS 6. Module names,
options, and flag behavior will be respected for the life of the stable
release series.
Backwards compatibility: Scripts written for newer versions of GRASS 6.4
may not work with earlier versions of GRASS 6 if they use commands which
were introduced later in the series. Other than that, they should be fine.
API compatibility: While GRASS 6's core C library API is reasonably stable
(at time of writing it has not changed in 16 months) it is not guaranteed.
ABI compatibility is typically not maintained and compiled C and C++ modules
will need to be recompiled after an upgrade in GRASS version. Changes to the
source code should not be needed however, most changes are simply the
addition of new functionality and care has been taken to avoid the
repurposing or removal of old functions or libraries.
The GRASS Python library: It is still in development, and Python 3 is just
around the corner, so you can expect a few changes but starting with GRASS
6.4.3 the core scripting library API is expected to remain mostly stable.
SWIG access to the GRASS C libraries has now been removed and replaced by
the ctypes library.
Compatibility with GRASS 7: Not guaranteed. It is suggested to use a
separate directory for your GRASS 7 addons, or name your custom scripts with
the version number in the name. If you wish to write dual-compatible
scripts, the g.version module and GRASS_VERSION environment variable are
available for parsing at run-time.
EXAMPLES
Download and install i.landsat.toar into the current GRASS addons directory:
g.extension r.out.kml
BUGS
This is a relatively new module and obtaining successful behavior on all platforms is
rather tricky. Please report any problems to the GRASS bug tracker. If this automatic
build fails, instructions for compiling both the GRASS source code and GRASS addons by
hand can be found in the GRASS wiki.
Note that Bourne shell and Python scripts can simply be downloaded from the online
Subversion repository browser and moved into your GRASS_ADDON_PATH directory by hand. On
UNIX you will likely need to set the executable bit using chmod before the script will
run. In this case the associated usage section of the help page will not be created.
Installing addon Python scripts on MS Windows is still experimental and is not guaranteed
to work properly at run-time due to association of ".py" file extensions with python.exe.
It is possible to run them, but be aware that you will typically need to call them with
".py" as part of the module name.
SEE ALSO
The GRASS Addons module listing in the GRASS Wiki
The wxGUI extension manager (found in the Settings menu)
Details on contributing modules you have written to the GRASS addons
repository can be found in the GRASS Development Wiki
AUTHORS
Markus Neteler
Martin Landa
Hamish Bowman
Last changed: $Date: 2013-07-03 11:25:54 +0200 (Wed, 03 Jul 2013) $
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