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I have seen -- used in the compgen command.

For example:

compgen -W "foo bar baz" -- b

What is the meaning of the --.

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3 Answers 3

up vote 132 down vote accepted

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 "-v" like this:

grep -- -v file
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1  
Most notably in the Bash set built-in, where it's absolutely necessary. –  l0b0 Oct 18 '12 at 9:03
3  
-- works to separate options from regular expressions in grep, but the canonical way is to use -e/--regexp. –  l0b0 Oct 18 '12 at 9:05
    
@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 as grep -e -v file (although that is very confusing). –  Guss Jan 21 at 16:12

This marks end of parameter (option) list.

http://linux.about.com/library/cmd/blcmdl1_compgen.htm

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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, and test builtins do not accept options and do not treat -- specially. The exit, logout, break, continue, let, and shift builtins 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 echo does not interpret -- to mean the end of options.

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