From https://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html,
-(A hyphen.) Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell
itself (such as the -i option).
I am not sure what it says. Can you give some examples for the meaning of a hyphen parameter?
Answers:
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Method 1
You can echo $- to see the currently-enabled shell options:
$ echo $- himBH
Those are options you can provide with a - on shell invocation — bash -h -B — or later on using set.
The flags are defined in the documentation for set. My options above are:
-h
Locate and remember (hash) commands as they are looked up
for execution. This option is enabled by default.-m
Job control is enabled (see Job Control). All processes
run in a separate process group. When a background job
completes, the shell prints a line containing its exit status.-B
The shell will perform brace expansion (see Brace Expansion).
This option is on by default.-H
Enable ‘!’ style history substitution (see History
Interaction). This option is on by default for interactive shells.
and i for an interactive shell.
If I change the active options, say with set -x, I’ll get a new value of $-:
$ set -x +h $ echo $- imxBH
Method 2
It depends – as a dollar-sign expansion, $- expands to a list of the current shell’s settable single-letter options – such as -x and -f and -C. For an example, an interactive shell will expand it at least like:
echo "$-"
i
The longer, set -o option versions can be had with set +o.
But there is another kind of hyphen-special-parameter which is a sort of analog to this. You can use two consecutive hyphens to signal the end of options in a typical command’s argument list, but you can also use a single-hypen to do the same for a POSIX-shell. Historically, shells accepted a single hyphen to mean much the same.
A bash shell interprets a single-hyphen specially in argument list-contexts. With set, for example it marks the end of options and disables -verbose and -xtrace. Additionally, set - does not clear a parameter list if it is the first and only argument to set as set -- would.
A login shell will often append a - to its argv[0].
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