[patch] Remove superfluous /dev/null on grep line

[Jonathan Wakely]

On 06/04/16 11:01 +0200, Jakub Jelinek wrote:
>On Wed, Apr 06, 2016 at 09:50:48AM +0100, Jonathan Wakely wrote:
>> On 06/04/16 09:39 +0200, Eric Botcazou wrote:
>> >we recently ran into build failures on Windows systems using a somewhat old
>> >grep, coming from a syntax error in the libstdc++-symbols.ver version file:
>> >
>> ># Symbol versioning for shared libraries.
>> >if ENABLE_SYMVERS
>> >libstdc++-symbols.ver:  ${glibcxx_srcdir}/$(SYMVER_FILE) \
>> >		$(port_specific_symbol_files)
>> >	cp ${glibcxx_srcdir}/$(SYMVER_FILE) $@.tmp
>> >	chmod +w $@.tmp
>> >	if test "x$(port_specific_symbol_files)" != x; then \
>> >	  if grep '^# Appended to version file.' \
>> >	       $(port_specific_symbol_files) /dev/null > /dev/null 2>&1; then
>> >\
>> >	    cat $(port_specific_symbol_files) >> $@.tmp; \
>> >	  else \
>> >	    sed -n '1,/DO NOT DELETE/p' $@.tmp > tmp.top; \
>> >	    sed -n '/DO NOT DELETE/,$$p' $@.tmp > tmp.bottom; \
>> >	    cat tmp.top $(port_specific_symbol_files) tmp.bottom > $@.tmp; \
>> >	    rm tmp.top tmp.bottom; \
>> >	  fi; \
>> >	fi
>> >
>> >Note the double /dev/null on the grep command line.  The first one causes the
>> >grep to fail when the command is invoked on these systems.  That's old code,
>> >but it is now invoked for config/abi/pre/float128.ver on the mainline and 5
>> >branch and this breaks the build on these systems (4.9 builds fine).
>> >
>> >This first /dev/null doesn't serve any useful purpose and seems to be a typo,
>>
>> Doesn't it mean that if $port_specific_symbol_files contains only
>> whitespace we don't hang waiting for input from stdin? The 'if' above
>> it will be true when "x$port_specific_symbol_files" = "x " or similar.
>>
>> I don't see any way for that to happen in the FSF tree, so it should
>> be safe. I'm a bit concerned about making that change this late in
>> stage 4 though. There isn't much time to find out if it breaks an
>> obscure target.
>
>As it is a make variable, can't make be used to test this?
>So perhaps
>	chmod +w $@.tmp
>ifneq ($(port_specific_symbol_files),)
>	  if grep '^# Appended to version file.' \
>	       $(port_specific_symbol_files) /dev/null > /dev/null 2>&1; then \
>	    cat $(port_specific_symbol_files) >> $@.tmp; \
>	  else \
>	    sed -n '1,/DO NOT DELETE/p' $@.tmp > tmp.top; \
>	    sed -n '/DO NOT DELETE/,$$p' $@.tmp > tmp.bottom; \
>	    cat tmp.top $(port_specific_symbol_files) tmp.bottom > $@.tmp; \
>	    rm tmp.top tmp.bottom; \
>	  fi;
>endif
>?  Though, I think the initial and trailing whitespace is removed during
>expansion (or already parsing of the vars), so even the
>test "x$(port_specific_symbol_files)" != x
>check should work right.

OK, I have no objection to the original patch then.