Re: printf \045 (or whatever the character code for % is)

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Jan 5,  5:39pm, Peter Stephenson wrote:
}
} > POSIX's description assumes that the backslash escapes and format
} > specifications are processed in one pass and simply says that an
} > octal escape sequence shall write the corresponding byte. If they
} > are separate passes the backslash escape removal step needs to know
} > about percent signs.
} 
} That's a reasonable assumption, but the function handling print is an
} appalling mess so it's not easy to fix without a major rewrite.

The octal escapes are all handled by getkeystring().  There's already
a special macro GETKEYS_PRINTF_FMT which (unfortunately?) is used for
both "printf" and "print -f".

} The code for printf doesn't really have any business being associated
} with the code for print, they're there for different purposes entirely
} based on completely different specifications. At the moment printf
} does the same as 'print -f', so it has all the same oddities as print
} whether it should or not.

I'm not entirely sure that's true.  The printf builtin doesn't accept
any options, which means that except for the initial getkeystring(),
nearly everything in bin_print() is ignored until you get down to the
part that handles the format spec ... and that can't be replaced by
e.g. sprintf() because of misc. special formats like %b and %q.

} (In my opinion, anyone deliberately asking for combined print and
} printf behaviour deserves everything they get so I'm perfectly happy
} to let 'print -f' fester while standardising printf.)

Although we could rip the format handling out of bin_print() and
create a new bin_printf() [which would be called by "print -f"?] we'd
still need something akin to getkeystring() for the octal escapes.

} However, I never get volunteers for tidying the shell up, so we're
} probably stuck until someone gets fed up enough to look into it.

GETKEYS_PRINTF_FMT expands to GETKEY_OCTAL_ESC|GETKEY_BACKSLASH_C ...
seems as though an additional flag to getkeystring() could be used to
cause \045 to expand to %% as a special case, something like this in
utils.c:

@@ -5517,6 +5522,8 @@
 		    }
 		    *t++ = zstrtol(s + (*s == 'x'), &s,
 				   (*s == 'x') ? 16 : 8);
+		    if ((how & GETKEY_PRINTF) && t[-1] == '%')
+		        *t++ = '%';
 		    if (svchar) {
 			u[3] = svchar;
 			svchar = '\0';

The flag bits for "how" are an enum in zsh.h and I'm undecided whether
to renumber them or just add another to the end, so I have't included
a complete patch.  Also I don't know whether the intent is that \045
(and \x25) should become %% only for "printf" or also for "print -f",
so no patch for builtin.c yet either.

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