Defining and Redefining Pattern Rules

You define an implicit rule by writing a pattern rule. A pattern rule looks like an ordinary rule, except that its target contains the character ‘%’ (exactly one of them). The target is considered a pattern for matching file names; the ‘%’ can match any nonempty substring, while other characters match only themselves. The prerequisites likewise use ‘%’ to show how their names relate to the target name.

Thus, a pattern rule ‘%.o : %.c’ says how to make any file stem.o from another file stem.c.

Note that expansion using ‘%’ in pattern rules occurs after any variable or function expansions, which take place when the makefile is read. See How to Use Variables, and Functions for Transforming Text.

• Pattern Intro		An introduction to pattern rules.
• Pattern Examples		Examples of pattern rules.
• Automatic Variables		How to use automatic variables in the recipe of implicit rules.
• Pattern Match		How patterns match.
• Match-Anything Rules		Precautions you should take prior to defining rules that can match any target file whatever.
• Canceling Rules		How to override or cancel built-in rules.