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

[Bernhard Voelker]

On 7/24/19 4:30 PM, Eric Blake wrote:
> On 7/24/19 6:28 AM, James Youngman wrote:
>> On Tue, Jul 23, 2019 at 7:51 PM 積丹尼 Dan Jacobson <address@hidden> wrote:
>>>
>>> OK.
>>> But I now "demand" that xargs add a --show-quoting or whatever argument,
>>
>> Your demand must be presented in the form of a patch.
> 
> Is a new option necessary, or can we just use gnulib's quotearg() module
> unconditionally?  I guess the only reason to make it a new command-line
> option would be to allow the user to specify which of the quotearg
> styles they prefer to see (for reference, 'ls --quoting-style=WORD' is a
> good example of producing various representations of the output to avoid
> ambiguities).  If we do use gnulib's quotearg module, we also benefit
> from QUOTING_STYLE in the environment regardless of whether we add a
> command-line option.

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"));
     }

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)".

Do you see any drawback / corner case?

Have a nice day,
Berny