On Wed, Nov 25, 2009 at 11:01 PM, Paul Smith <psm...@gnu.org> wrote: > On Wed, 2009-11-25 at 19:59 -0600, Peng Yu wrote: >> Suppose I have 'command.sh' that generate files 'a' and 'b'. >> >> If either of 'a' or 'b' is older than 'command.sh', I need to run >> 'command.sh' again. The following Makefile has two targets, right? I >> want to refer to the second target 'b' in this Makefile. >> >> $ cat Makefile >> all: a b >> >> a b: command.sh >> ./command.sh > > You seem to be under the impression that this rule means that make will > invoke your command.sh one time only, and believe that it generates two > different files. > > That's not what this means. > > The rule you've written above is _identical_ to, just shorthand for, > writing this: > > a: command.sh > ./command.sh > b: command.sh > ./command.sh > > So, in this case, there is only one target file each time command.sh is > invoked, and the name of that target will be stored in $...@. So the first > time command.sh is invoked, $@ will be set to "a" and the second time it > will be set to "b".
I don't understand the following case. If there are two rules, why command.sh is only executed once. $ touch command.sh $ make ./command.sh If there are multiple files that are generated by command.sh, are you suggesting to write a single rule for an arbitrarily chosen single file? But if I only have a rule for 'a' but not for 'b', when the file 'b' is deleted, 'command.sh' will not called by make. But I do want make to updated 'b'. How do you deal with this case? a: command.sh ./command.sh _______________________________________________ Help-make mailing list Help-make@gnu.org http://lists.gnu.org/mailman/listinfo/help-make
