> It is the behaviour of GNU GetOpt, which is very widely used and
> understood.
No, it isn't. At least, it's not the default. The GNU libc manual
encourages the use of getopt_long(). It also provides an alternative
called getopt_long_only() for programs that want to be backward
compatible.
Here's the relevant bit from the libc manual:
Since long option names were used before before the `getopt_long'
options was invented there are program interfaces which require
programs to recognize options like `-option value' instead of
`--option value'. To enable these programs to use the GNU getopt
functionality there is one more function available.
-- Function: int getopt_long_only (int ARGC, char *const *ARGV,
const char *SHORTOPTS, const struct option *LONGOPTS, int
*INDEXPTR)
The `getopt_long_only' function is equivalent to the
`getopt_long' function but it allows to specify the user of the
application to pass long options with only `-' instead of `--'.
The `--' prefix is still recognized but instead of looking
through the short options if a `-' is seen it is first tried
whether this parameter names a long option. If not, it is
parsed as a short option.
Assuming `getopt_long_only' is used starting an application
with
app -foo
the `getopt_long_only' will first look for a long option named
`foo'. If this is not found, the short options `f', `o', and
again `o' are recognized.
--
/jaap