Re: xargs prompts with the same string, but executes differently

[Eric Blake]

On 7/24/19 4:20 PM, Bernhard Voelker wrote:

> I agree that another new option is way too much.  That question to the user
> is meant for interactive use only anyway, so what about simply:
> 
> diff --git a/xargs/xargs.c b/xargs/xargs.c
> index 913328b8..85084123 100644
> --- a/xargs/xargs.c
> +++ b/xargs/xargs.c
> @@ -1093,7 +1093,7 @@ print_args (bool ask)
> 
>    for (i = 0; i < bc_state.cmd_argc - 1; i++)
>      {
> -      if (fprintf (stderr, "%s ", bc_state.cmd_argv[i]) < 0)
> +      if (fprintf (stderr, "%s ", quotearg_n_style (0, 
> shell_escape_quoting_style, bc_state.cmd_argv[i])) < 0)
>         die (EXIT_FAILURE, errno, _("Failed to write to stderr"));

Looks reasonable to me (other than line wrapping).

>      }
> 
> Example:
> 
>   $ printf '%s\0' 000 '0 0' '0"0' "0'0" \
>       | xargs/xargs -0p '-I{}' echo hello '{}' world
>   echo hello 000 world ?...y
>   hello 000 world
>   echo hello '0 0' world ?...y
>   hello 0 0 world
>   echo hello '0"0' world ?...y
>   hello 0"0 world
>   echo hello "0'0" world ?...y
>   hello 0'0 world
> 
> Well, this also changes plain -t output (i.e., without -p), but it's not
> that bad actually: it doesn't seem to be specified anywhere how -t output
> should look like.  Just in case, we could still guard quotearg_n_style
> by "if (ask)".

POSIX merely says that -p implies -t, so I argue that consistency
between the two is better than only doing it for -p. I also agree that
POSIX doesn't seem to have any hard rules about what the format should
be, so doing the quoting unconditionally looks compliant.

> 
> Do you see any drawback / corner case?

Not so far.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

signature.asc
Description: OpenPGP digital signature