Changing macro definitions in a command

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When macros in the shell commands are defined in the description file, you can change the values that the make command assigns to the macro.

To change the assignment of the macro, put a : (colon) after the macro name, followed by a replacement string. The form is as follows:

$(macro:string1=string2)

where string1 is either a suffix or a word to be replaced in the macro definition and string2 is the replacement suffix or word.

When the make command reads the macro and begins to assign the values to the macro based on the macro definition, the command replaces each string1 in the macro definition with a value of string2. For example, if the description file contains the macro definition:

FILES=test.o sample.o form.o defs

You can replace the form.o file with a new file, input.o, by using the macro in the description-file commands, as follows:

cc -o $(FILES:form.o=input.o)

You can all replace all the suffixes .o in the macro with .c as follows:

cc -c $(FILES:.o=.c)

The macro values can also be changed using pattern matching replacements of the following form:

$(macro: op%os= np%ns)

Where op is the existing (old) prefix, os is the existing (old) suffix, np is the new prefix, and ns is the new suffix.

op, os, np and ns can be a string of zero or more characters. The pattern matched by the percent sign (%) on the left-hand side of the equal-sign, which is a string of zero or more characters, is used with np and ns to replace the macro value. The percent sign (%) operator can appear any number of times on the right-hand side of the equal sign (=).

For example:

FOO=abc def 
BAR=$(FOO:%=dir1/%.o dir1/%_cltn.o)

sets the value of BAR to dir1/abc.o dir1/abc_cltn.o dir1/def.o dir1/def_cltn.o

Changing the value of a macro in this manner is useful when maintaining archive libraries. For more information, see the ar command.