ENH: Added ReleaseNotes, ChangeLog and INSTALL

[freefoam.git] / INSTALL

FreeFOAM Installation Instructions for Version 0.1.0
====================================================
Michael Wild <themiwi@users.sourceforge.net>
v0.1.0, 15 May 2009
:Author Initials: MW
:linkcss!:
:numbered:
http://freefoam.sourceforge.net

Building FreeFOAM
-----------------
- Install the prerequisites documented in the link:README.html[README] file. If
  your distribution does not have 'METIS', 'ParMetis', 'MGRIDGEN' or 'libccmio'
  be not worried, FreeFOAM can handle those for you.
- Download the FreeFOAM source and unpack it somewhere convenient. For the
  further instructions we will use +$HOME/Source/+.
+
---------------------------------------------------------------------------
$ mkdir -p $HOME/Source
$ cd $HOME/Source
$ wget http://switch.dl.sourceforge.net/sourceforge/freefoam/freefoam-0.1.0rc1.tar.bz2
$ tar xjf freefoam-0.1.0.tar.bz2
---------------------------------------------------------------------------
- Create a build tree and _cd_ into it:
+
---------------
$ mkdir $HOME/Source/freefoam-0.1.0-build
$ cd $HOME/Source/freefoam-0.1.0-build
---------------
- Start CMake-configuration:
+
---------------
$ ccmake $HOME/Source/freefoam-0.1.0
---------------
- Press the +c+ key. Use the arrow keys to navigate up and down and press
  +enter+ to edit a field. To commit the change, press +enter+ again, or +ESC+
  to abandon the change.  ON/OFF fields are toggled by pressing +enter+.
  Advanced options can be displayed by hitting the +t+ key.
  * Set +CMAKE_BUILD_TYPE+ to 'Release' for an optimized build.
  * If CMake complains that it can't find MPI, and you don't want to install it, disable
    +FF_USE_MPI+. If, instead, you want to use GAMMA or PVM, enable +FF_USE_GAMMA+ or
    +FF_USE_PVM+, respectively. You can also enable more than one of the options.
+
[NOTE]
Currently only MPI implementation is available.
+
  * Select the default Pstream implementation by setting +FF_DEFAULT_PSTREAM+
    to one of 'dummy', 'mpi', 'pvm' or 'gamma'. This setting will only influence
    the contents of the <<globalconfig,global 'controlDict' file>>.
  * If CMake told you it couldn't find ParaView:
    . Set +ParaView_DIR+ to the path of the directory containing
    'ParaViewConfig.cmake', which is most likely the ParaView build directory.
    . If you do not want to build the ParaView plug-ins, disable
    +FF_BUILD_PARAVIEW_PLUGINS+
  * If you do not have 'METIS' or 'ParMetis', enable
    +FF_BUILD_PRIVATE_METIS+ or +FF_BUILD_PRIVATE_PARMETIS+, respectively.
    CMake will then try to download and build the selected libraries for you.
    Conversely, if one of the libraries is provided by your system, you can turn
    the respective setting to 'OFF'. Please note that if your system provides
    only 'ParMetis', you do not have to install 'METIS', as the former also
    contains 'METIS' in an older version.
  * If you want to use the 'MGridGen' agglomeration method for the GAMG solver,
    you need to enable +FF_ENABLE_PARMGRIDGEN+ and if the library is not
    installed on your system ensure that +FF_BUILD_PRIVATE_PARMGRIDGEN+ is
    enabled. See <<parmgridgen,above>> regarding the unknown license status of
    this package.
  * In order to build 'ccm26ToFoam', a conversion utility for grids generated
    with 'ProStar/ccm' (C) version 2.6, enable the setting +FF_ENABLE_CCMIO+
    and if 'libccmio' is not installed on your system, also
    +FF_BUILD_PRIVATE_CCMIO+.  Refer to the <<libccmio,above>> description of
    the 'libccmio' package for the license restrictions which apply to this
    package.
  * If you plan on installing FreeFOAM, set +CMAKE_INSTALL_PREFIX+ to the base directory
    under which FreeFOAM should reside.
  * For more fine-grained control over what gets installed where, adjust
    +FF_INSTALL_CONFIG_PATH+, +FF_INSTALL_HEADER_PATH+, +FF_INSTALL_LIB_PATH+,
    +FF_INSTALL_FRAMEWORK_PATH+, +FF_INSTALL_PV3FOAMREADER_PATH+,
    +FF_INSTALL_PVFOAMREADER_PATH+ and +FF_INSTALL_USERDFOAM_PATH+. Paths not
    starting with a slash ('/') will be relative to 'CMAKE_INSTALL_PREFIX'. If
    you include a leading slash, the paths are absolute.
  * If you want FreeFOAM to use 'float' as the floating point type instead of
    'double', change +FF_DOUBLE_PRECISION+ to 'OFF'.
- Hit the +c+ key again. If you enabled +FF_BUILD_PRIVATE_CCMIO+, CMake will fail
  to download https://wci.llnl.gov/codes/visit/3rd_party/libccmio-2.6.1.tar.gz.
  Please follow the instructions in the error message on how to work around this
  problem, or download the file manually and place it in +ThirdParty/ccmio/+
  (relative to the build directory). Then hit +c+ again.
- You shouldn't get any errors anymore now. Keep pressing +c+ until ccmake
  displays "++Press [g] to generate and exit++" in the legend at the bottom of
  the interface.
- Press +g+ to generate the Makefiles and exit the ccmake interface.
- Start the native build tool. If you used the 'Makefile' generator
  (which is the default for Unix-platforms), type
+
----------------
$ make
----------------
- If you have a multi-core/processor machine, you can speed things up
  significantly by telling Make to run independent jobs in parallel.
  A good choice for the number of parallel jobs to run is the
  number of CPU's/cores you have in your machine plus 1 (to compensate
  for disk-latency). For a typical dual-core machine, run
+
----------------
$ make -j3
----------------

Installing FreeFOAM
-------------------
If you want to, you can now install FreeFOAM. Depending on the
+CMAKE_INSTALL_PREFIX+ and the individual +FF_INSTALL_*_PATH+ it is possible
that you have to do this as root, i.e. use +su+ or +sudo+.
---------------
$ make install
---------------

Using FreeFOAM
--------------
If you didn't change +CMAKE_INSTALL_PREFIX+ and +FF_INSTALL_BIN_PATH+ chances
are that you can start using FreeFOAM right after you installed it without any
further steps being necessary.

[[globalconfig]]
Global Configuration Files
~~~~~~~~~~~~~~~~~~~~~~~~~~
Unfortunately the OpenFOAM library (on which FreeFOAM builds) and some
applications require some files to be present for start-up. It finds those
in the following places (in the specified order, picking the first hit):

1. Under the directory specified in the +$FREEFOAM_CONFIG_DIR+ environment
   variable
2. In '$HOME/.FreeFOAM/0.1'
3. In '$HOME/.FreeFOAM'
4. In the installation directory of the configuration files. There are
   two possible places for this:
+
   '<CMAKE_INSTALL_PREFIX>/<FF_INSTALL_CONFIG_PATH>':: if you specified
     +<FF_INSTALL_CONFIG_PATH>+ as a relative path.
    '<FF_INSTALL_CONFIG_PATH>':: if you specified +<FF_INSTALL_CONFIG_PATH>+ as
    an absolute path.
+
The default location is '/usr/local/etc/FreeFOAM/1.0'.

Selecting the Parallel Communications Library
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Both, FreeFOAM and OpenFOAM abstract the parallel operations into the 'Pstream'
library, making it rather simple to firstly switch between parallel
implementations and secondly port the software to a new communications library.
However, FreeFOAM uses a much more flexible mechanism of determining which
'Pstream' implementation library to use than OpenFOAM. The latter does this by
adjusting the +LD_LIBRARY_PATH+ environment variable.  As FreeFOAM wants to be a
well behaved Linux citizen, this is not an option. Instead, FreeFOAM dynamically
loads the desired 'Pstream' library at startup (i.e. as a plug-in).  The
following list details how FreeFOAM determines what library to load (if at all):

1. If the environment variable +FREEFOAM_PSTREAM_LIBRARY+ is set,
   FreeFOAM will try to load the library specified by it.
2. If the sub-dictionary +PstreamImplementation+ exists in the global
   'controlDict' file (see <<globalconfig,'Global Configuration Files'>>), it
   reads the value of the entry +configName+ therein. It then expects that a
   sub-dictionary of +PstreamImplementation+ with the name specified in
   +configName+ exists. If that sub-dictionary contains the entry +library+, it
   will try to load a library specified by the value of that entry.

After FreeFOAM (possibly) loaded the library, it will try to instantiate
concrete implementations of the abstract base classes +PstreamImpl+,
+IPstreamImpl+ and +OPstreamImpl+. Which classes are to be instantiated
is determined as follows:

1. FreeFOAM queries the environment variables +FREEFOAM_PSTREAM_CLASS+,
   +FREEFOAM_IPSTREAM_CLASS+ and +FREEFOAM_OPSTREAM_CLASS+ for the class
   names to be instantiated.
2. For any of the variables not set,  it requires the sub-dictionary
   +PstreamImplementation+ to be present in the global 'controlDict', reads the
   value of +configName+ and similarly to the library loading, loads the
   sub-dictionary specified by that value. It then expects to find the entries
   +Pstream+, +IPstream+ and +OPstream+ which specify the names of the classes
   to load.

This means that one can create a global 'controlDict' file containing
(among other things) something like the following:
=========
---------
PstreamImplementation
{
    //configName dummy;
    configName mpi;

    dummy
    {
        library libdummyPstream.so;
        Pstream dummyPstreamImpl;
        OPstream dummyOPstreamImpl;
        IPstream dummyIPstreamImpl;
    }

    mpi
    {
        library libmpiPstream.so;
        Pstream mpiPstreamImpl;
        OPstream mpiOPstreamImpl;
        IPstream mpiIPstreamImpl;
    }
}
---------
=========

This way the administrator can provide a global 'controlDict' in the FreeFOAM
installation. Every user can then override that 'controlDict' by supplying her
own file in her home directory as detailed in <<globalconfig,'Global
Configuration Files'>>. In order to select a particular 'Pstream' implementation
for a specific communications library, the user can then either adjust the
+PstreamImplementation::configName+ entry in the global 'controlDict' file, set
the +FREEFOAM_PSTREAM_CONFIG+ variable or for full control, set the variables
+FREEFOAM_PSTREAM_LIBRARY+, +FREEFOAM_PSTREAM_CLASS+, +FREEFOAM_IPSTREAM_CLASS+
and +FREEFOAM_OPSTREAM_CLASS+.

Running FreeFOAM From the Build Tree
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You can use FreeFOAM without installing it first, directly from the build tree.
However, this might take a little bit more effort to set up because most likely
you will have to adjust the following environment variables:

PATH:: Must contain '$HOME/Source/freefoam-0.1.0-build/bin'
LD_LIBRARY_PATH:: Must contain '$HOME/Source/freefoam-0.1.0-build/lib/FreeFOAM/0.1'
FREEFOAM_CONFIG_DIR:: Should point to '$HOME/Source/freefoam-0.1.0-build/etc'

Where it is assumed that you followed the <<installation,installation instructions>>. If
you used different paths for downloading and compiling FreeFOAM, you will have
to adjust these names. Refer to <<environment,'Extending Search Paths And
Setting Environment Variables Permanently'>> if you need help setting these
variables.

Running the tutorials
---------------------
Now you should be able to run the tutorial cases. For this copy the +tutorials+
directory to some convenient place:
---------------
$ mkdir -p $HOME/FreeFOAM/$LOGNAME-0.1/run
$ cp -r $HOME/Source/freefoam-0.1.0-build/tutorials $HOME/FreeFOAM/$LOGNAME-0.1/run/
$ cd $HOME/FreeFOAM/$LOGNAME-0.1/run
---------------
And try to run e.g. the 'cavity' tutorial case:
---------------
$ cd icoFoam
$ blockMesh -case cavity
$ checkMesh -case cavity
$ icoFoam -case cavity
---------------
Things should run smoothly and finish without an error.

Obtaining the Source Code from the GIT repository
-------------------------------------------------
- Clone the FreeFOAM repository (here the clone is placed in
  +$HOME/Source/FreeFOAM+):
+
---------------------------------------------------------------------------
$ mkdir -p $HOME/Source
$ git clone git://repo.or.cz/freefoam.git $HOME/Source/FreeFOAM
---------------------------------------------------------------------------
- Proceed in the same way (replacing the path names apropriately) as in the
  above build instructions.

Build Configuration Reference
-----------------------------
[glossary]
+CMAKE_BUILD_TYPE+::
  One of '<empty>', 'Debug', 'Release', 'RelWithDebInfo' and 'MinSizeRel'.
  Refer to the CMake documentation for more detail.
+FF_DOUBLE_PRECISION+::
  If set to 'ON' FreeFOAM will be compiled using 'double' as the
  floating point type. If set to 'OFF' it will use 'float'.
+FF_BUILD_FRAMEWORK+::
  If this is enabled, the libraries are built as frameworks. Only available on Mac OS X.
+CMAKE_INSTALL_PREFIX+::
  Installation prefix under which to install FreeFOAM.
+FF_INSTALL_BIN_PATH+::
  Installation path of the binaries. If not absolute, it is relative to
  'CMAKE_INSTALL_PREFIX'.
+FF_INSTALL_CONFIG_PATH+::
  Installation path of the configuration files. If not absolute, it is
  relative to 'CMAKE_INSTALL_PREFIX'.
+FF_INSTALL_HEADER_PATH+::
  Installation path of the header files. If not absolute, it is
  relative to 'CMAKE_INSTALL_PREFIX'. On Mac OS X, and if
  'FF_BUILD_FRAMEWORK' is enabled, this setting is ignored.
+FF_INSTALL_LIB_PATH+::
  Installation path of the libraries. If not absolute, it is
  relative to 'CMAKE_INSTALL_PREFIX'.
+FF_INSTALL_FRAMEWORK_PATH+::
  Installation path of the Mac OS X frameworks. If not absolute, it is
  relative to 'CMAKE_INSTALL_PREFIX'. This is only available and takes
  effect if FreeFOAM is compiled on Mac OS X, and if
  'FF_BUILD_FRAMEWORK' is enabled.
+FF_INSTALL_PV3FOAMREADER_PATH+::
  Installation path of the ParaView3 plug-ins. If not absolute, it is
  relative to 'CMAKE_INSTALL_PREFIX'.
+FF_INSTALL_PVFOAMREADER_PATH+::
  Installation path of the ParaView2 plug-ins. If not absolute, it is
  relative to 'CMAKE_INSTALL_PREFIX'.
+FF_INSTALL_USERDFOAM_PATH+::
  Installation path of the Ensight plug-in. If not absolute, it is
  relative to 'CMAKE_INSTALL_PREFIX'.
+EXECUTABLE_PREFIX+::
  Prefix which get prepended to the name of the executables. This defaults to
  'ff_' and serves the disambiguation of names.
+FF_USE_GAMMA+::
  If enabled, FreeFOAM will use the GAMMA parallel communications library.
+FF_USE_MPI+::
  If enabled, FreeFOAM will use the MPI parallel communications library.
  This is required in order to build some of the libraries and utilities.
+FF_USE_PVM+::
  If enabled, FreeFOAM will use the PVM parallel communications library.
+FF_DEFAULT_PSTREAM+::
  The default Pstream selection in the global 'controlDict' file.
+FF_BUILD_PARAVIEW_PLUGINS+::
  Whether to build the ParaView plug-ins. If enabled, FreeFOAM requires a
  ParaView build tree and the 'ParaView_DIR' variable set to the path of it.
[[enable-ccmio]]
+FF_ENABLE_CCMIO+::
  Enable the use of 'libccmio'. This is required to build the grid conversion
  utility 'ccm26ToFoam'.
+
[WARNING]
The license of 'libccmio' (C) is proprietary and requires the consent of the
copyright holders (http://www.cd-adapco.com[CD-adapco]) to download and use the
library. Further it is not allowed to redistribute it in any form. The request
for permission of inclusion with http://debian.org[Debian] was answered as
follows by mailto:geoffrey.prewett@us.cd-adapco.com[Geoffrey Prewett]:
+
--------------------------------------------------------------------------------
Gerber,

Sorry for the delay in response.  I checked back with our development director,
and he felt that it would be best to not include libccmio with Debian.
Instead, we would prefer to continue our current policy and keep it on our
web/FTP and have people ask for it.  There are three reasons for this:

1) We don't support STAR on Debian, and don't want to give the impression that we do.
2) We would like to keep a list of people that we give the library to.
3) This is not a general purpose library;  its sole purpose is to communicate
between our products.  Accepting outside changes risks committing a change that
would break our own software in possibly subtle ways.

So I regret to tell you that my company has declined to permit libccmio to be
distributed as part of Debian.

Regards,
Geoff Prewett
--------------------------------------------------------------------------------
+
+FF_BUILD_PRIVATE_CCMIO+::
  Automatically download and build libccmio. Unfortunately this process will
  fail in the download step, since CMake currently does not support 'https'
  URLs. But you will get specific instructions from the build system on how to
  get around this problem.
+FF_BUILD_PRIVATE_METIS+::
  Automatically download and build 'METIS'.
+FF_BUILD_PRIVATE_PARMETIS+::
  Automatically download and build 'ParMetis'.
[[enable-parmgridgen]]
+FF_ENABLE_PARMGRIDGEN+::
  Enable the use of 'PARMGRIDGEN' and 'MGRIDGEN' which is required to build
  'MGridGenGamgAgglomeration' providing the 'MGridGen' agglomeration method for
  the GAMG solver.
+
[WARNING]
The license of 'MGRIDGEN' and 'PARMGRIDGEN' is unknown and the upstream authors
so far have not answered any inquiries to resolve the issue. If you enable the
use of 'MGRIDGEN' and 'PARMGRIDGEN' you alone are responsible for ensuring that
you don't violate any license conditions applying to these libraries. The
authors of FreeFOAM will and cannot take any responsibility for your
actions.
+
+FF_BUILD_PRIVATE_PARMGRIDGEN+::
  Automatically download and build 'PARMGRIDGEN' and 'MGRIDGEN'.
+FF_BUILD_DOXYGEN_DOCS+::
  Enable building of the 'Doxygen API documentation'. The documentation will
  only be built once and is not updated automatically. This is because it
  depends on a huge number of files and would make dependency tracking very
  slow and difficult to maintain. To force the re-generation of the API
  documentation execute +make apidoc+.

Troubleshooting
---------------

The FreeFOAM Executables Are Not Found By The Shell
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are three possible reasons for this:

1. Your shell (notably 'csh', 'tcsh' and 'zsh') requires you to refresh the
   cache of available executables. You can do so by entering the command:
+
--------------
$ rehash
--------------
+
2. If 'rehashing' didn't solve the problem, the problem most likely is that you
   installed FreeFOAM into a non-standard location by changing the configuration
   variables +CMAKE_INSTALL_PREFIX+ or +FF_INSTALL_BIN_PATH+ in which case the
   executables where installed into a directory not searched by the shell. In
   this case you have to add the installation directory of the executables to
   the +PATH+ variable. There are two possible locations:
+
--
'<CMAKE_INSTALL_PREFIX>/<FF_INSTALL_BIN_PATH>':: if you specified
  +FF_INSTALL_BIN_PATH+ as a relative path
'<FF_INSTALL_BIN_PATH>':: if you specified +FF_INSTALL_BIN_PATH+ as an absolute
  path
--
+
After extending the +PATH+ variable with the installation directory of the
executables, you should be able to run all FreeFOAM applications as any other
binary available on the system. See <<environment,'Extending Search Paths And
Setting Environment Variables Permanently'>> for
instructions on how to extend the search path.

3. This option is similar to the previous solution and applies if you want to
   run FreeFOAM from the build tree (i.e. without running +make install+). In
   this case you again have to make sure that your shell finds the executables
   built by CMake by extending the +PATH+ variable. Further, you have to tell
   FreeFOAM where to find the global configuration files (see
   <<globalconfig,'Global Configuration Files'>>). Here, you have the option to
   place the files under your home directory or set an environment variable. The
   former can be achieved by:
+
--------------
$ mkdir -p $HOME/.FreeFOAM/0.1
$ cp $HOME/Source/freefoam-0.1.0-build/etc/controlDict $HOME/.FreeFOAM/0.1
$ cp $HOME/Source/freefoam-0.1.0-build/etc/cellModels $HOME/.FreeFOAM/0.1
$ cp -r $HOME/Source/freefoam-0.1.0-build/etc/thermoData $HOME/.FreeFOAM/0.1
--------------
+
The latter (and recommended) method is to set the environment variable
+FREEFOAM_CONFIG_DIR+ to '$HOME/Source/freefoam-0.1.0-build/etc'. Adjust paths to the
build tree to your actual setup.

Starting Any FreeFOAM Application Fails Because Some Libraries Cannot Be Found
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Although CMake should have taken care of this by using +RPATH+ on Linux and
+install_name+ on Mac OS X, it might be necessary on some systems to adjust the
library search paths:

+LD_LIBRARY_PATH+:: This variable is used by all Unix like systems (e.g. Linux,
  Mac OS X, etc.)
+DYLD_LIBRARY_PATH+:: This variable is used by Mac OS X.

If you installed FreeFOAM, there are (as with the executables), two possible
installation directories:

'<CMAKE_INSTALL_PREFIX>/<FF_INSTALL_LIB_PATH>':: if you specified
  +FF_INSTALL_LIB_PATH+ as a relative path.
'<FF_INSTALL_LIB_PATH>':: if you specified +FF_INSTALL_LIB_PATH+ as an absolute
  path.

If you are trying to run from the build tree, you have to include
'$HOME/Source/freefoam-0.1.0-build/lib/FreeFOAM/0.1' in the above mentioned search
paths (where you have to adjust the location of the build tree to your actual
setup).

A Running FreeFOAM Application Aborts Because It Can't 'dlopen' A Library
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
FreeFOAM (and OpenFOAM) often dynamically load libraries at run-time (a.k.a
plug-ins) to add features the user requested without requiring that the whole
application be recompiled. This makes it very simple to add new boundary
conditions, turbulence and combustion models etc. However, it also requires that
FreeFOAM must be able to find these libraries at run-time. The operating system
function which does the loading of the libraries ('dlopen') usually tries to
find the library with the given name in several places; namely a default search
path and a search path configured by one or multiple environment variables such
as +LD_LIBRARY_PATH+ or +DYLD_LIBRARY_PATH+ (on Mac OS X). The details vary from
platform to platform, so you best consult the documentation of 'dlopen' for the
details.

Additionally FreeFOAM allows you to configure a custom search path for plug-ins
in the <<globalconfig,global 'controlDict'>> file by listing the directories to
be searched in the list +LibrarySearchPaths+. By default FreeFOAM is configured
to search for plug-ins in the location where CMake installed them.

If you want to add your own plug-in libraries (e.g. you want to add your own
boundary conditions class), you most probably will want to extend this search
path.

[[environment]]
Extending Search Paths And Setting Environment Variables Permanently
--------------------------------------------------------------------
The way one sets environment variables and extends the executable and library
search paths permanently strongly depends on the shell used. Usually one has to
create or change an initialization file in the users home directory. In the
following this will be discussed very briefly for the popular shells 'BASH' and
'tcsh'.  However, if you need more help or want information on using the shell,
there is an excellent tutorial available at http://linuxcommand.org.

BASH
~~~~
The BASH shell is the default shell for most Linux/Unix distributions. Most
systems configure the BASH shell such that it reads the text file
'$HOME/.bashrc' when starting up, so this is the place where one appends
customizations of the environment variables. On some systems this file is not
processed by default (notably Mac OS X). In this case you can use
'$HOME/.bash_profile'.

Referencing A Variable
^^^^^^^^^^^^^^^^^^^^^^
To retrieve the value stored in a shell variable or environment variable, one
prefixes its name with the dollar (+$+) character.

Setting A Variable
^^^^^^^^^^^^^^^^^^
The syntax for setting a variable and making it available to child-processes of
the shell is the following:
-------
$ export variable_name=variable_value
-------
Note that no white-space characters are allowed surrounding the +=+ sign.

Extending A Search Path
^^^^^^^^^^^^^^^^^^^^^^^
The shell and other Unix system facilities use environment variables to locate
executables and dynamically linked libraries. These search paths consist of
strings naming directories in which the executables and libraries should be
searched for. The individual paths are separated by a colon (+:+) character. To
add the e.g. the directory '$HOME/bin' to the search path for executables, one
would do the following:
-------
$ export PATH=$PATH:$HOME/bin
-------
which appends '$HOME/bin' to the end of the +PATH+ variable.

TCSH
~~~~
Some users and administrators prefer to use a 'C-Shell', such as the TCSH. Here
you can use e.g. the file '$HOME/.tcshrc' to customize the environment.

Referencing A Variable
^^^^^^^^^^^^^^^^^^^^^^
As with the BASH, one retrieves the value stored in a shell variable or
environment variable by prefixing its name with the dollar (+$+) character.
Sometimes it is also necessary to protect the variable name by surrounding it
with curly braces (+{+ and +}+).

Setting A Variable
^^^^^^^^^^^^^^^^^^
The syntax for setting a variable and making it available to child-processes of
the shell is the following:
-------
$ setenv variable_name variable_value
-------

Extending A Search Path
^^^^^^^^^^^^^^^^^^^^^^^
The shell and other Unix system facilities use environment variables to locate
executables and dynamically linked libraries. These search paths consist of
strings naming directories in which the executables and libraries should be
searched for. The individual paths are separated by a colon (+:+) character. To
add the e.g. the directory '$HOME/bin' to the search path for executables, one
would do the following:
-------
$ setenv PATH ${PATH}:${HOME}/bin
-------
which appends '$HOME/bin' to the end of the +PATH+ variable.  Note that
'C-shells' usually require the user to type 'rehash' after changing the +PATH+
variable to update the cache of available programs.

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