TeX/LaTeX looks at the TEXINPUTS environment variable to look for additional locations to search for included/referenced files. Therefore, new classes/styles can be easily added as follows:

1. Create a directory for the files:
   

   $ mkdir -p $HOME/tex/latex

2. Place the new class files into that folder (each class can be in its own directory and contain subdirectories):
   

   $ cp -a fancy-class $HOME/tex/latex/

3. Export the TEXINPUTS variable and also add it to your $HOME/.bash_profile:
   

   $ export TEXINPUTS=.:$HOME/tex/latex//:$TEXINPUTS

The ‘.’ ensures that the working directory is included in the search path. The double-‘//’ tells bash to also include files in subdirectories of ‘$HOME/tex’ recursively.

New BibTeX files can also be added locally in a similar fashion. The variables to set are then BSTINPUTS and BIBINPUTS.

The environment variable to set for MakeIndex styles is: INDEXSTYLE.

Source: AstroNat – Installation at The Smithsonian/NASA Astrophysics Data System

UPDATE [16 July 2009] The Kpathsea manual provides a wealth of information about usable environment variables.

$ rpm -ivh --relocate OLDPATH1=NEWPATH1 [--relocate OLDPATH2=NEWPATH2 ...] \
      --badreloc package.rpm

where OLDPATH is the path in the package; and NEWPATH is something like /home/user/userroot/usr, etc.

It’s best to run

$ rpm -qpl package.rpm

to see exactly which paths are going to be used by the package. For example, if the package foo.rpm produces:

$ rpm -qpl foo.rpm
/usr/bin/foo
/usr/lib/foo.so.0.0
/usr/lib/foo.so.0
/usr/share/doc/foo/README

then the steps needed are:

$ mkdir -p ~/myroot/usr/bin ~/myroot/usr/lib ~/myroot/usr/share/doc
$ rpm -ivh --relocate /usr=/home/$USER/myroot/usr --badreloc foo.rpm

That’ll install the package under the hierarchy ~/myroot. There will some errors from rpmdb but this is fine since the rpmdb is in a filesystem that we do not have write access to. The only repercussion is that rpm will have no record of the package foo being installed (so packages will have to be removed by hand); but that’s okay since we cannot possibly mess up the system while installing stuff under our own home dirs.

The only steps remaining are to add the new paths to the binary and library search paths. To so this, add the following lines to ~/.bash_profile

        PATH=$PATH:$HOME/myroot/usr/bin
        LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$HOME/myroot/usr/lib

        export PATH LD_LIBRARY_PATH

This is only efficient as long as the package does not have too many unmet dependencies — since you will need to grab and install all missing dependencies along with the package itself. And even if you had installed some of the dependencies earlier using this method, rpm will not know about it since there will be no entry in the system rpmdb.