[ -e $VAR ]
True if variable holds and existing file (file or directory)
[ -f $VAR ]
True is variable holds an existing regular file
[ -d $VAR ]
True is variable holds an existing directory
[ -x $VAR ]
True if variable is an executable file
[ -L $VAR ]
True variable holds path of a symlink
[ -r $VAR ]
True if variable holds file that is readable
[ -w $VAR ]
True if variable holds file that is writable