GNU Info

(make.info)Empty Targets

---

Next: Special Targets Prev: Force Targets Up: Rules

---

Enter node , (file) or (file)node

Empty Target Files to Record Events
===================================

   The "empty target" is a variant of the phony target; it is used to
hold commands for an action that you request explicitly from time to
time.  Unlike a phony target, this target file can really exist; but
the file's contents do not matter, and usually are empty.

   The purpose of the empty target file is to record, with its
last-modification time, when the rule's commands were last executed.  It
does so because one of the commands is a `touch' command to update the
target file.

   The empty target file should have some prerequisites (otherwise it
doesn't make sense).  When you ask to remake the empty target, the
commands are executed if any prerequisite is more recent than the
target; in other words, if a prerequisite has changed since the last
time you remade the target.  Here is an example:

     print: foo.c bar.c
             lpr -p $?
             touch print

With this rule, `make print' will execute the `lpr' command if either
source file has changed since the last `make print'.  The automatic
variable `$?' is used to print only those files that have changed
(Note: Automatic Variables.).