missing backslash escaping in AC_TRY_EVAL yields binary data in config.log with dash

[Vincent Lefevre]

I originally reported this bug in libtool:

  https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21309

but this actually seems to be a bug in AC_TRY_EVAL (or another macro
it uses).

Under Debian/unstable, with autoconf 2.69, I get binary data in the
config.log for MPFR due to \1 and \2 in echo strings (POSIX says
"if any of the operands contain a <backslash> character, the results
are implementation-defined.", thus dash is not broken here).

When doing "sh -x ./configure" (-x to get a trace), I get:

[...]
+ nlist=conftest.nm
+ eval echo "$as_me":7267: "/usr/bin/nm -B conftest.o \| sed -n -e 's/^.*[ 
]\([ABCDGIRSTW][ABCDGIRSTW]*\)[ ][ ]*\([_A-Za-z][_A-Za-z0-9]*\)$/\1 \2 \2/p' | 
sed '/ __gnu_lto/d' \> conftest.nm"
+ echo configure:7267: /usr/bin/nm -B conftest.o \| sed -n -e 's/^.*[ 
]\([ABCDGIRSTW][ABCDGIRSTW]*\)[ ][ ]*\([_A-Za-z][_A-Za-z0-9]*\)$/\1 \2 \2/p' | 
sed '/ __gnu_lto/d' \> conftest.nm
[...]

In libtool.m4, this comes from:

    nlist=conftest.nm
    if AC_TRY_EVAL(NM conftest.$ac_objext \| "$lt_cv_sys_global_symbol_pipe" \> 
$nlist) && test -s "$nlist"; then

the buggy output being done by AC_TRY_EVAL.

-- 
Vincent Lefèvre <address@hidden> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)