Overrides for makefile rules

Rule coverage is often used in makefiles. Similarly, a target may have multiple prerequisites. This dependency can be put together or specified separately.

Example 1:

test1:
    @echo "test111"

test2:
    @echo "test222"

test3:
    @echo "test333"

hehe: test1 test2 test3
    @echo "get hehe"

test: hehe

In the above example, for the target hehe , there are multiple prerequisites: test1 test2 and test3 , and the dependent targets will be parsed in turn during make.

The result after running is:

Here are the rules:

hehe: test1 test2 test3

It can also be formulated separately.

Example 2:

test1:
    @echo "test111"

test2:
    @echo "test222"

test3:
    @echo "test333"

hehe: test1
hehe: test2
hehe: test3
    @echo "get hehe"

test: hehe

The result of such an operation:

It can be seen that the results in Example 1 and Example 2 are the same.

From the above two examples, we can see that for the target hehe , the command is only used once. What will happen if it is replaced with two commands?

Example 3:

test1:
    @echo "test111"

test2:
    @echo "test222"

test3:
    @echo "test333"

hehe: test1
    @echo "11111"
hehe: test2
    @echo "22222"
hehe: test3

test: hehe

Take a look at the results of the operation:

From the results we conclude that:

Different dependencies of the same target in makefile rules can be specified separately;
Dependencies in makefile rules can be superimposed, but commands can only be covered;
The first dependency target of makefile is determined according to the final command, and other dependencies are in order;

Through example 3 , it is determined that the final command is echo 22222 , and the dependent target is test2 at this moment, so test2 will be the first dependent target of hehe, and the others follow the order of definition.

Example 4:

test1:
    @echo "test111"

test2:
    @echo "test222"

test3:
    @echo "test333"

hehe: test1
hehe: test2
hehe: test3
    @echo "3333"

test: hehe

Take a look at the results of the operation:

From the example, although test3 is the last dependency, because of the command, test3 will be the first dependency, and other dependencies are in the order of definition.