What is the double dash in this bash script excerpt doing

Question

I\'m looking at an excerpt of bash and I\'m trying to understand what exactly is happening here, particularly in the COMPREPLY assignment:

 case         


        

Answer 1

compgen is a bash builtin command, and the man pages say:

Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options.

Since $cur is a variable that contains options (starting with -), the -- is required (as mentioned in the man pages) to make a distinction between compgen options and input to be processed.

The following command is turning the option --d in --debug:

compgen -W '-a -d -f -l -t -h --aoption --debug --file --log --test --help --' -- --d
--debug

If you remove the separator --, the command throws an error, because compgen doesn't have any option starting with --d:

compgen -W '-a -d -f -l -t -h --aoption --debug --file --log --test --help --' --d
-bash: compgen: --: invalid option
compgen: usage: compgen [-abcdefgjksuv] [-o option]  [-A action] [-G globpat] [-W wordlist]  [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] [word]

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The ;; is a separator used in the case, esac statement to terminate in your example the section started with -*). Look at bash man pages for Compound Commands to get more info.