Re: [Help-bash] How to understand "set --"?

[Eric Blake]

On 02/18/2014 09:12 PM, Peng Yu wrote:
> Hi,
> 
> "help set" says
> 
>       --  Assign any remaining arguments to the positional parameters.
>           If there are no remaining arguments, the positional parameters
>           are unset.

Let's say you want to have $1 contain a literal "-x".  You do this by
either:

set dummy -x; shift         # portable to really old pre-POSIX sh

or by:

set -- -x                   # portable to all POSIX shells

The -- said to treat the next argument as the thing to place in $1, even
if that argument would normally be treated specially by set if the --
were not present.

> 
> But it seems that the above definition is not clear enough to explain
> the following output. Can anybody provide a better definitive
> explanation of "set --"? Should it be better to interpret the single
> quote in $x when "set --" is called?
> 
> ~/linux/test/bash/man/builtin/set/--$ x="'abc def'"
> ~/linux/test/bash/man/builtin/set/--$ set -- $x

Underquoted.  You called:

set -- "'abc" "def'"

because you forgot to quote $x.  The rules about -- do not change the
rules about quoting, only about whether a leading - is interpreted by
set as an option instead of crammed into $1.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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