I have seen -- used in the compgen command.
For example:
compgen -W "foo bar baz" -- b
What is the meaning of the -- in there?
More precisely, a double dash (--) is used in bash built-in commands and many other commands to signify the end of command options, after which only positional parameters are accepted.
Example use: lets say you want to grep a file for the string -v - normally -v will be considered the option to reverse the matching meaning (only show lines that do not match), but with -- you can grep for string -v like this:
grep -- -v file
-
2
-
7
--works to separate options from regular expressions ingrep, but the canonical way is to use-e/--regexp. – l0b0 Oct 18 '12 at 9:05 -
4@l0b0: the pattern to search is normally one of the positional parameters, so it can fit after the
--, though you are correct in noting that my example above could also be written asgrep -e -v file(although that is very confusing). – Guss Jan 21 '15 at 16:12 -
2Not all
bashbuiltin commands accept--as the end of option marker.[andechodon't for instance (one of the reasonsechocan't be used reliably). – Stéphane Chazelas Mar 21 '16 at 10:06
This marks end of parameter (option) list.
In man bash we can read in Shell Builtin Commands section:
Unless otherwise noted, each builtin command documented in this section as accepting options preceded by
-accepts--to signify the end of the options.The
:,true,false, andtestbuiltins do not accept options and do not treat--specially. Theexit,logout,break,continue,let, andshiftbuiltins accept and process arguments beginning with-without requiring--. Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with-as invalid options and require--to prevent this interpretation.Note that
echodoes not interpret--to mean the end of options.
POSIX.1-2017
12.2 Utility Syntax Guidelines
Guideline 10:
The first -- argument that is not an option-argument should be accepted as a delimiter indicating the end of options. Any following arguments should be treated as operands, even if they begin with the '-' character.
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_02
