'git rev-parse --parseopt' input format is fully text based. It has two parts,
separated by a line that contains only `--`. The lines before the separator
-(should be more than one) are used for the usage.
+(should be one or more) are used for the usage.
The lines after the separator describe the options.
Each line of options has this format:
------------
-<opt_spec><flags>* SP+ help LF
+<opt_spec><flags>*<arg_hint>? SP+ help LF
------------
`<opt_spec>`::
* Use `!` to not make the corresponding negated long option available.
+`<arg_hint>`::
+ `<arg_hint>`, if specified, is used as a name of the argument in the
+ help output, for options that take arguments. `<arg_hint>` is
+ terminated by the first whitespace. When you need to use space in the
+ argument hint use dash instead.
+
The remainder of the line, after stripping the spaces, is used
as the help associated to the option.
foo some nifty option --foo
bar= some cool option --bar with an argument
+baz=arg another cool option --baz with a named argument
+qux?path qux may take a path argument but has meaning by itself
An option group Header
C? option C with an optional argument"
eval "$(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)"
------------
+
+Usage text
+~~~~~~~~~~
+
+When `"$@"` is `-h` or `--help` in the above example, the following
+usage text would be shown:
+
+------------
+usage: some-command [options] <args>...
+
+ some-command does foo and bar!
+
+ -h, --help show the help
+ --foo some nifty option --foo
+ --bar ... some cool option --bar with an argument
+ --bar <arg> another cool option --baz with a named argument
+ --qux[=<path>] qux may take a path argument but has meaning by itself
+
+An option group Header
+ -C[...] option C with an optional argument
+------------
+
SQ-QUOTE
--------