Re: [PATCH 4/6] tweak to config.status->libtool quoting (correct?)

[Eric Blake]

Paolo Bonzini <bonzini <at> gnu.org> writes:

> This is a patch I was not sure of when I wrote it, but now I am more
> confident.  config.status was looking for quoting only in the first
> word of variables because of a missing "..." in the arguments of $ECHO.
> $ECHO, depending on how it is set (and always in the final patch) will
> not print arguments after the first.

In Autoconf, AS_ECHO (and thus $as_echo) is documented as printing only a 
single shell word.  You are correct that it is not safe to pass multiple 
arguments to $ECHO, and that "" (or other quoting) is needed to make it one 
shell word.  'printf %s\\n' actually prints multiple arguments, but that is not 
the only plausible definition of as_echo.

> 
> The first hunk is needed for the other patches, but the second does the
> same change, and the current code seems equally wrong.  Note that not
> applying this patch is a showstopper for the final patch in the series,
> which defines variables like
> 
>     printf %s\\n "$1"
> 
> There, the first word does not need extra quoting, but the others do.
> 
> * libltdl/m4libtool.m4 (_LT_OUTPUT_LIBTOOL_COMMANDS_INIT): Double
> quote ECHO-ed variable.
> 
> ---
>  libltdl/m4/libtool.m4 |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libltdl/m4/libtool.m4 b/libltdl/m4/libtool.m4
> index 34fa517..27c8d70 100644
> --- a/libltdl/m4/libtool.m4
> +++ b/libltdl/m4/libtool.m4
> @@ -520,7 +520,7 @@ compiler='$compiler_DEFAULT'
>  # Quote evaled strings.
>  for var in lt_decl_all_varnames([[ \
>  ]], lt_decl_quote_varnames); do
> -    case \`eval \\\\\$ECHO "X\\\\\$\$var"\` in
> +    case \`eval \\\\\$ECHO \\\\""X\\\\\$\$var"\\\\"\` in
>      *[[\\\\\\\`\\"\\\$]]*)

This might be a bit easier to write (and thus review) if we used AS_ESCAPE 
rather than supplying all the \ ourselves (perhaps as an independent patch 
prior to this one).  As in:

pre:
AS_ESCAPE([
  case `eval \\$ECHO "X\\\$$var"` in
...
], [\`$])

post:
AS_ESCAPE([
  case `eval \\$ECHO \""X\\\$$var\""` in
...
], [\`$])

or even nested AS_ESCAPE:

AS_ESCAPE([
  case `eval AS_ESCAPE(['$ECHO "X$'])$var[]AS_ESCAPE(['"'])` in
...
], [\`$])


At any rate, the patch indeed makes sense - $var contains a variable name, 
which may expand with whitespace, so we must supply literal "" as part of the 
string being eval'd in order to protect the expansion of $var as a single shell 
word (all within the context of `` needing one level of escapes, and a here-doc 
needing another).

-- 
Eric Blake