Substitution References

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Substitution references

A substitution reference substitutes the value of a variable with alterations that you specify. It has the form $(var: a= b) or {var:a=b}, and its meaning is to take the value of the variable, var, replace every a at the end of a word with b in that value, and substitute the resulting string. When we say at the end of a word, we mean that a must appear either followed by whitespace or at the end of the value in order to be replaced; other occurrences of a in the value are unaltered. Consider the following statement.

foo := a.o b.o c.o
bar := $(foo:.o=.c)

This input sets bar toa.c b.c c.c. See Setting variables. A substitution reference is actually an abbreviation for use of the patsubst expansion function (see Functions for string substitution and analysis). We provide substitution references as well as patsubst for compatibility with other implementations of make.

Another type of substitution reference lets you use the full power of the patsubst function. It has the same form $(var:a=b) described above, except that now a must contain a single % character. This case is equivalent to $(patsubst a, b,$(var)). See Functions for string substitution and analysis for a description of the patsubst function. Consider the following example.

foo := a.o b.o c.o
bar := $(foo:%.o=%.c)

This statement sets bar toa.c b.c c.c.

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