On Thu, 18 Feb 1999, Martin Buchholz wrote: [ I didn't realize there would be a quiz. ] argv[0] is not required to contain anything meaningful. Your shell may pass more or less useful information in $0. Nice shells pass more. From execv man page (Linux 2.0.35), typos and all: The execv and execvp functions provide an array of point- ers to null-terminated strings that represent the argument list available to the new program. The first argument, by convention, should point to the file name associated with the file begin executed. The array of pointers must be terminated by a NULL pointer. You can execl("/bin/ls", "ha-ha", "-l", 0), though it might give ls a headache if it doesn't know its name. Mostly, $0 will be either a relative or absolute path to yourself, but it depends on the shell/execer. A perl module (FindBin) does some further sanity checks: Check if $0 exists. Make it absolute if relative. If $0 is only a basename "cat", search for $0 in $PATH to get the fullpath of $0 (this last check would be pointless if trying to get the dir of $0, of course). Fail if all of these attempts fail. -Justin vallon(a)mindspring.com

On Thu, 18 Feb 1999 02:00:19 EST, Justin Vallon said: And the shell itself is often on the receiving end of argv[0] games. By convention, /bin/login sets argv[0] to be '-' followed by the shell name, and this is how your login shell knows that it's a login shell. Don't forget that argv[0] may be the name of a symlink in some directory other than the one we're in - I've seen more than one Unixoid where /usr/ucb/newaliases is a symlink to /usr/lib/sendmail. /Valdis