Re: [PATCH] Supplant the "while case ... break ;; esac" idiom

From: David Kastrup <dak@gnu.org>
Date: Sep 24, 2007, 08:29 UTC
Message-ID: <867imgwjne.fsf@lola.quinscape.zz>
In-Reply-To: <20070924080134.GA9112@artemis.corp>

Pierre Habouzit <madcoder@debian.org> writes:

Show 22 quoted lines

> On Mon, Sep 24, 2007 at 07:57:31AM +0000, David Kastrup wrote:
>> "David Symonds" <dsymonds@gmail.com> writes:
>> 
>> > On 24/09/2007, David Kastrup <dak@gnu.org> wrote:
>> >> Mike Hommey <mh@glandium.org> writes:
>> >>
>> >> > On Sun, Sep 23, 2007 at 10:42:08PM +0200, David Kastrup wrote:
>> >> >> -while case $# in 0) break ;; esac
>> >> >> +while test $# != 0
>> >> >
>> >> > Wouldn't -ne be better ?
>> >>
>> >> Why?
>> >
>> > Because -ne does a numeric comparison, != does a string comparison,
>> > and it's a numeric comparison happening, semantically speaking.
>> 
>> I don't see the point in converting $# and 0 into numbers before
>> comparing them.  "!=" is quite more readable, and the old code also
>> compared the strings.
>
>   Fwiw $# already is a number.

It isn't.

> Hence test $# -ne 0 is definitely a better test.

/* TEST/[ builtin. */
int
test_builtin (list)
     WORD_LIST *list;
{
  char **argv;
  int argc, result;

  /* We let Matthew Bradburn and Kevin Braunsdorf's code do the
     actual test command.  So turn the list of args into an array
     of strings, since that is what their code wants. */
  if (list == 0)
    {
      if (this_command_name[0] == '[' && !this_command_name[1])
	{
	  builtin_error ("missing `]'");
	  return (EX_BADUSAGE);
	}

      return (EXECUTION_FAILURE);
    }

  argv = make_builtin_argv  (list, &argc);
  result = test_command (argc, argv);
  free ((char *)argv);

  return (result);
}

>   $# != 0 would yield sth like (strcmp(sprintf("%d", argc), "0"))
>   $# -ne 0 would yield sth like (argc != atoi("0")).
>
>   Not that it matters much, but the latter looks better to me.

Not to me. The code does not support your argument, and all $x expansions certainly are strings, according to manual and usage. I will rework the patch this evening in order to get a commit message more placable to Junio, and I will at his request remove all of the (redundant) quoting. But removing quoting from $# does not turn it into a number: it remains the same string '0'. If someone else feels he should replace all "=" and "!=" tests for "numeric" comparisons with the unreadable numeric tests, he can go ahead proposing a separate patch that should not just cover $#.

You can have bash declare numeric variables, but even they are strings (they just auto-evaluate on assignment):

declare -i nonsense nonsense="3+$(echo 4)" echo "$nonsense"

gives 7, even though everything has been "strings" here.

-- 
David Kastrup