rehash regenerates the system's cached info about what's contained in the system PATH. Commonly needed after installing new applications from the ports tree. Example:
ph34r# cd /usr/ports/net/rsync ph34r# make install ph34r# rsync --version rsync: Command not found. ph34r# rehash ph34r# rsync --version rsync version 2.6.2 protocol version 28 Copyright (C) 1996-2004 by Andrew Tridgell and others <http://rsync.samba.org/> Capabilities: 64-bit files, socketpairs, hard links, symlinks, batchfiles, IPv6, 32-bit system inums, 64-bit internal inums rsync comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to redistribute it under certain conditions. See the GNU General Public Licence for details.