Re: Trees and forests problem found but on how to solve it.

[Ted Stern]

On 10 Apr 2006 10:24:18 -0700, BILLY PATTON wrote:
>
> I have this :
> define refresh_proj_bb_sub
> $(1)+$(2)+$(3)+$(4) :
>         cdir='$(CURDIR)' ; \
>         $(CD) $(SRC_TREE)/$(2)/$(3)/$(4) ;\
>         for X in $($(call merge,+,$(call uc,$(1)) $(2) $(3) $(4))) ; do
> \
>           if test -f $$$$X ; then \
>                 $(EXEC_LOG) -proj $(2) -bb $(3) $(PVCS_GET)
> -v$(3)$(PVCS_VER) $$$$X ; \
>           fi ; \
>         done ; \
>         $(CD) $$$$cdir
> endef
>
> When $($(call merge,+,$(call uc,$(1)) $(2) $(3) $(4))) produces the
> names of 
> a variable (a list) and this variable does not exist the result, from
> warning, is:
> CR inserted for readability
> cdir='/home/users/bp1497' ; 
> cd v0506/SOURCE_TREE/ldb/celltools/pub ; 
> for X in  ; 
> do 
>   if test -f $X ; then 
>     /home/users/bp1497/exec_log -log 
>        /home/users/bp1497/v0506/log.2010115843 
>           -proj ldb -bb celltools 
>            /home/pvcs/vm/hpux/bin/get -vcelltools05.06.00.00 $X ; 
>   fi ; 
> done ; 
> cd $cdir
>
>
> Notice at the for X in  is empty.
>
> This list does not exist.
>
> So how can I set this up to see that the list exists?

Modify your /bin/sh syntax slightly:

       for X in $($(....)) /dev/null ; do \
          if test -s $$$$X ; then \
              ... ; \
          endif ; \
       done ; \
       ...

In other words, add a file to your Bourne shell 'for' loop list that
always exists but is always empty.  'test -s file' tests to see if the
file exists and is of size > 0.  Since you have added /dev/null to
your shell file list, the list will never be null, but /dev/null will
never pass the 'if test -s' test and won't perturb the results.

This is a common shell trick, for example when you do something like

     find . -print | egrep '\.(some|filename|regexp)$' | \
          xargs egrep '(some|expression)' /dev/null

I.e., you filter a 'find' list for some filename type, then past the
list to egrep, but add /dev/null so that there are always at least 2
files to grep through.  This ensures that, just in case only one file
matches, grep or egrep will include the filename before the match.

Ted          
-- 
 dodecatheon at gmail dot com
 Frango ut patefaciam -- I break so that I may reveal