Revision history
    2020-12-26 : Version 1.15: Change behaviour when a command exists in a previous version but not in the selected one. A warning is displayed to advise the user about the risk.

    2020-01-01 : Version 1.14: Support of osversion containing system/version

    2019-12-25 : Version 1.13b: update web site and email reference

    2019-12-23 : Version 1.13: update to be compatible with recent compiler

    2005-10-03 : Version 1.12b: bug #868448 is reworked. apv command is now really compatible with strict mode of perl 5.8 + help page of apv-lib corrected. It is now possible to execute a command after loading an environmnent with the apv -s option.

    2004-01-02 : Version 1.12a: bug #868448 is now solved. apv command is now compatible with strict mode of perl 5.8

    2003-09-22 : Version 1.12: A feature is added. There is now the possibility
    to prefix commands by setting the APVSYS_PREFIXCMD variable. This variable
    can only be set *IN an ap-environment file*.

    2003-08-11 : Version 1.11: circular reference detected. If, for any rason, 
    a command is not available anymore, ApVSys will stop immediately instead 
    of looping infinitely. 

    2003-06-10 : Version 1.10: uname -m can be optionaly taken into account in the 
    toolpath. in this case uname -r is joined to uname -m with an underscore.

    2003-06-10 : Version 1.01: bug #752152 fixed

    2003-06-09 : Version 1.00: feature request (bug #750493) implemented. It is now possible
    to manually specified the O.S. version name (to use instead of the output of uname -r)
    in the /etc/apvsys.conf/osversion file.
    (by the way the variable APVSYS_OSVERSION can also be used, see the manpage)
    
    2003-06-07 : Version 0.99i: bug #750492 fixed, the operating system where /dev
    does not exist are now supported in csh debug mode.

    2003-02-23 : Version 0.99h: Clean up of apv.pl, some improvements in apvsys-config.pm 
    to be CYGWIN compliant, option -L added in apv-linktool.pl for logging
    purpose, option -W is added to apv.pl to print the list of versions in
    a table.

    2003-01-19 : Version 0.99g: warn msg redirected to stdout. An example is added 
    in the apv manpage for the new feature of apv -l (this filtering feature 
    is optimized for flexlm to increase its flexibility).

    2003-01-15 : Version 0.99f: a debug print is removed in apvsys-lmstat
    and the bug #666175 is re-fixed :-( correctly...I hope!

    2003-01-12 : Version 0.99e: 'bug' #663702 fixed by a new option
    'apv -L | apv --full-lmstat'. New feature for lmstat is implemented 
    to filter the feature(s) to display.
    
    2003-01-11 : Version 0.99d: bug #666175 fixed, the APVSYS_TARGET
    variable is now set when "apv -d" is called.
  
    2003-01-06 : Version 0.99c: apv-regtool was modified for CYGWIN:
    the extension ".exe" are removed from the commands db during the
    registration process(under CYGWIN only) to be CYGWIN compliant.
    bug #666255 fixed
    
    2002-12-13 : Version 0.99b: apv-osmirror bug fixed for the option
    -t all, option -L added in apv-osmirror

    2002-10-17 : Version 0.99 : First version that supports Cygwin. The
    examples in the manpage and the help of apv-osmirror are corrected.

    2002-09-13 : Version 0.98 : bug #609110 fixed, the toolspec interpre-
    tation is not stopped after an empty line anymore.

    2002-09-01 : Version 0.97 : shell option (apv -s) bug fixed when default
    command version is different of default tool version.

    2002-08-26 : Version 0.96 : shell option (apv -s) bug fixed when
    multi-environment must be loaded, apv -X improved. ApVSys "how to
    update" documented.

    2002-08-10 : Version 0.95 : space/tab are now accepted at the end of a
    toolspec line; modification in apv-xcheck documentation.

    2002-08-08 : Version 0.94 : -R option in apv bug fixed, apv -a now list
    the versions even if the toolspec has a bad version specified, new
    script apv-lib.

    2002-08-05 : Version 0.93 : more documentation, all the manpages are
    written.

    2002-06-28 : Version 0.92 : some new scripts (apv-setdefault,
    apv-dbcheck, apv-osmirror), options "--shell" and "--lmstat" are added
    in the apv interface.

    2002-05-24 : Version 0.91 : Comments in toolspec are supported. Some
    compatibility problems Solaris/Linux are solved in the new exec
    functions.

    2002-05-23 : Version 0.90 : Small bug fix in the apv interface and in
    the version-picker (when ApVSys command was started by a daemon).
    Documentation about ap-environment.

    2002-05-15 : Version 0.88 : Bug fix, there was an inconsistency when
    several toolspecs were defined.

    2002-05-14 : Version 0.87 : Some improvements in the installation
    script, minor bug fix in loadenv interface, minor modification to be
    HP-UX compatible.

    2002-05-13 : Version 0.86 : The first open-source beta-version. The
    documentation is not fully written

    Start point:

    The original idea was from Alex Farrell who developed a similar system
    fully written in perl. Because it was written for a big company, it was
    not open-source. I've taken the idea and I've fully re-thought and
    re-written the system in C.