arg0

Arg0 is a conventional label for the first entry in an argument vector provided to a program at startup. In most environments it stores the name or path used to invoke the program, and is distinct from subsequent arguments to the program.

In C and C++ programs, the main function commonly has the signature int main(int argc, char *argv[]). The element argv[0] contains the program name or the path used to execute it; argc includes that initial entry along with any additional arguments. In practice, argv[0] may be a full path, a relative path, or only the executable name, and it can differ from the binary’s actual file location if invoked via a symlink or via a shell wrapper.

In Python, sys.argv[0] is the script or module being executed, with subsequent items in sys.argv representing the remaining arguments. In many Unix shells, $0 holds the script or command name and $1, $2, etc. the positional parameters. The exact handling of arg0 varies by language and runtime, and not all environments expose a separate argv[0] in the same way.

Notes: The value of arg0 is implementation-dependent and is not standardized across languages. Some runtimes do not expose a distinct program-name entry or may omit it from the argument list. Arg0 is commonly used to derive resource paths relative to the program’s location or to display usage and error messages that reference the program’s name.

See also: argv, argc, main, command-line interface.