Sometime duplicate executable files or alias creates tons of confusion. To find out duplicated executables files you can use chkdupexe command.
It will scan the union of $PATH and a hardcoded list of common locations for binaries. It will report dangling symlinks and duplicately-named binaries.
Dangling symlink: /usr/bin/rmic Dangling symlink: /usr/bin/jar -rwxr-xr-x 1 root root 38936 Sep 23 2004 /usr/bin/nsupdate -rwxr-xr-x 1 root root 203960 Jan 26 2005 /usr/sbin/nsupdate -rwxr-xr-x 1 root root 15139 Apr 6 01:48 /sbin/grub-install -rwxr-xr-x 1 root root 6453 Apr 1 18:38 /usr/sbin/grub-install
As you see, it is quite easy to identify all those duplicates executables files. There is also some good discussion going on about PATH and aliases.
Updated for accuracy.