How to set system-wide environment variables

When installing software that is intended to be used by anyone on a paricular system, it is sometimes necessary to set system-wide environment variables. Red hat linux and several other operating systems provide an easy way to do that. You just put files foo.csh and foo.sh in a special directory /etc/profile.d. Using Pacman, one way to do this to bring these files with your installation and place them like so. 

downloadUntar('http://.../foo.tar.gz','TAR') # sets TAR to the untarred top directory
cd('$TAR')
cp('foo.csh','/etc/profile.d')
cp('foo.sh', '/etc/profile.d')
You don't have to worry about cleaning up such files. Pacman automatically takes care of "undo"-ing everything that you have done as long as it isn't a shell command.

Since the above will only work if you are root, it is nicer to do the following 

username('root')
downloadUntar('http://.../foo.tar.gz','TAR') # sets TAR to the untarred top directory
cd('$TAR')
cp('foo.csh','/etc/profile.d')
cp('foo.sh', '/etc/profile.d')
which requires that the installer be root before proceeding. This way, a non-root user get's a nicer message than a failure of the cp action. If you want to give the installer more information about what's going on here, just do 
{   username('root');
    downloadUntar('http://.../foo.tar.gz','TAR');
    cd('$TAR'); cp('foo.csh','/etc/profile.d'); cp('foo.sh', '/etc/profile.d') 
OR 
    fail("You must be root to set the system-wide enviros for the FOO package.") 
}
Now many, but not all operating systems use /etc/profile.d for this purpose. To fix this, you could use the platform atoms to branch depending on the operating system. A slightly sloppier thing to do is to just test if a directory /etc/profile.d exists. Also, since this action affects the whole system, you might want to ask permission first. 
{ exists('/etc/profile.d') OR fail("No /etc/profile.d directory.  Can't install FOO") }
{   username('root');
    downloadUntar('http://.../foo.tar.gz','TAR');
    {   yes('OK to copy files into /etc/profile.d as part of the installation of FOO?'); 
        cd('$TAR'); cp('foo.csh','/etc/profile.d'); cp('foo.sh', '/etc/profile.d')
    OR
        fail("Permission to copy files to /etc/profile.d has been declined.")
    }
OR 
    fail("You must be root to set the system-wide enviros for the FOO package.") 
}
Note that this code is safe in the sense that Pacman will never remove files or directories unless it has created them and undoing everything on uninstallation is automatic. Also, the argument to yes above is only asked of the user once. If the installer installs your package then, removes it and re-installs it or if the package is updated, Pacman remembers the answer to such questions.

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