Tilde expansion
---------------
A leading `~' in a path element is replaced by the value of the
environment variable `HOME', or `.' if `HOME' is not set.
A leading `~USER' in a path element is replaced by USER's home
directory from the system `passwd' database.
For example,
setenv TEXINPUTS ~/mymacros:
will prepend a directory `mymacros' in your home directory to the
default path.
As a special case, if a home directory ends in `/', the trailing
slash is dropped, to avoid inadvertently creating a `//' construct in
the path. For example, if the home directory of the user `root' is
`/', the path element `~root/mymacros' expands to just `/mymacros', not
`//mymacros'.
Tilde expansion is implemented in the source file `kpathsea/tilde.c'.