GNU `make'

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#### Directory Search and Implicit Rules

The search through the directories specified in `VPATH` or with `vpath` also happens during consideration of implicit rules (see Using Implicit Rules).

For example, when a file `foo.o` has no explicit rule, `make` considers implicit rules, such as the built-in rule to compile `foo.c` if that file exists. If such a file is lacking in the current directory, the appropriate directories are searched for it. If `foo.c` exists (or is mentioned in the makefile) in any of the directories, the implicit rule for C compilation is applied.

The commands of implicit rules normally use automatic variables as a matter of necessity; consequently they will use the file names found by directory search with no extra effort.