How does a program get its path name?

[Roberto Shironoshita]

In article <2933 at sdsu.UUCP> turtle at sdsu.UCSD.EDU (Andrew Scherpbier) writes:
> [Leisner.Henr at xerox.com's original article, <11923 at brl-adm.ARPA>,]
> [asking how cc knows to look at /lib for the passes              ]
>
> When a program executes, the full path to the executable file is
> kept in the zero-th argument.

I'm sorry, but this is plain and simply an overstatement.  It may be
right if the command was the full path, but not necessarily otherwise.

> If you have a declaration of main which looks like this:
>	main(argc,argv)
>	int	argc;
>	char	*argv[];
>
> then argv[0] is a pointer to the full path.

argv[0] contains whatever was passed as argv[0] to the exec family of
system calls.  According to AT&T's manual for SVR2 (of 04/84), the
convention is that it be either the full pathname or its last
component.  The behavior I've seen on both /bin/csh and /bin/sh under
Ultrix 2.0 and HCX/UX 3.0 (with universe both bsd and att) is that it
is whatever came as the command.  If you specify "cc" as your command,
strcmp (argv[0], "cc") == 0.

Thus, you can't say that argv[0] IS a pointer to the full path.  You
can't even say that it isn't (sigh!).

                                   Roberto Shironoshita

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