Re: FYI: fix dollar handling in func_quote_for_expand [libtool--devo--1.0--patch-265]

[Gary V. Vaughan]

Hi Noah,

Noah Misch wrote:
> On Wed, Oct 20, 2004 at 09:45:46PM +0100, Gary V. Vaughan wrote:
> 
> 
>>      (func_quote_for_eval): Four space indent margin for functions!
> 
> 
> Does this deserve mention in HACKING?

Yes, good point.  I'll do that presently.

>>  +# Save mangling of backslash escaped dollars by the above.  Running this
>>  +# substitution after double_quote_subst notices and corrects expansion
>>  +# of already escaped meta-chars.  \$x -> double_quote_subst -> \\$x,
>>  +# which doesn't protect $x from expansion.  To correct this we do:
>>  +# \\$x -> sed_double_backslash -> \\\$x, properly protecting $x.
>>  +sed_double_backslash='s/\([[^\\]]\)\\\\$/\1\\\\\\$/g'
> 
> 
> I am glad you caught that.  The first $ does need a \,

Oops.  Thanks.

> and I believe the \ in
> the character class does not need one.

Although GNU sed may manage without (I haven't checked), BSD sed does need it
(otherwise \] becomes an atom, and the character class is then unterminated).

> That said, this substitution handles
> 'x\$y', but it does not seem to handle '\$y' (no non-backslash preceding
> character) or 'x\\\$y'.  I believe this variant does so:
> 
> # Re-`\' parameter expansions in output of double_quote_subst that were
> # `\'-ed in input to the same.  If an odd number of `\' preceded a '$'
> # in input to double_quote_subst, that '$' was protected from expansion.
> # Since each input `\' is now two `\'s, look for any number of runs of
> # four `\'s followed by two `\'s and then a '$'.  `\' that '$'.  Note
> # that the embedded single quotes serve only to enhance readability.
> sed_double_backslash='s/\(\(^\|[^\]\)\(\\\\''\\\\''\)*\)''\\\\''\$/\1\\\\''\\''\$/g'

Indeed.  Excellent idea.  I hadn't thought of nesting capture groups like
that, and decided that multiple expressions to catch increasingly rare odd-
numbered backslash counts into $double_quote_subst wasn't worth the effort.
And I forgot about the left anchored \$x case altogether :-/

Unfortunately, alternation is not very portable (Apple's sed doesn't support
it at all), so we need two expressions.  The following works for me.  I'll
patch HEAD and branch-2-0 shortly if noone complains that it fails for them...

sed_double_backslash='
              s/^\(''\\\\''\\\\''\)*''\\\\''\$/\1''\\\\''\\$/;
    s/\([[^\\]]\(''\\\\''\\\\''\)*\)''\\\\''\$/\1''\\\\''\\$/g'

Cheers,
        Gary.
-- 
Gary V. Vaughan      ())_.  address@hidden,gnu.org}
Research Scientist   ( '/   http://tkd.kicks-ass.net
GNU Hacker           / )=   http://www.gnu.org/software/libtool
Technical Author   `(_~)_   http://sources.redhat.com/autobook

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