Re: echo "\\1"?

[Eric Blake <eblake@redhat.com>]

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On 07/27/2017 09:44 AM, Bosco wrote:
> I don't have any problem, I only show you one case where I had to fix
> an script in order to work a compilation in dash.
> 
> I'm using dash because of simplicity, unfortunately I don't understand
> how things work.
> 
> I think the problem is of dash, I only want to report that dash fails
> at parse scape sequence.
> For instance, the command
> 
>   echo \\\\
> 
> prints
> 
>   \

Correct, per POSIX.  Incorrect, for portable code (since not all echo
implementations obey POSIX; many require to type

echo -e \\\\

to get single output, but -e is not POSIX).

> 
> I think it should print
> \\

Wrong per POSIX, but it matches what you get on bash if you don't turn
on 'shopt -s xpg_echo' and 'set -o posix' simultaneously (yes, bash has
two separate knobs that BOTH have to be on to get POSIX behavior).

> 
> I don't have to decided how dash should understand things because it
> isn't my project. I only advise of a bad behavior, of course from my
> point of view.

The bad behavior is not in dash, but in your non-portable use of echo
with a \ in the argument.  Use printf instead, if you want your script
to work in more than one shell.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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