argv0 - run a program with a specified 0th argument
argv0 realname zero [ arg ... ]
argv0 runs the program stored as realname on disk, with the given arguments. It sets the 0th argument of the program to zero.
argv0 /bin/csh -bin/csh
runs /bin/csh with a 0th argument of -bin/csh. csh will think it is a login shell and behave accordingly.
argv0 can be used to run some inetd wrappers under tcpserver.