Brief Introduction to wildcard notdir patsubst in makefile

1. wildcard: Extended wildcard
2. notdir: remove the path
3. patsubst: Replace the wildcard character

Example:
Create a test directory and create a subdirectory named sub under the test directory.
$ Mkdir Test
$ CD Test
$ Mkdir sub

Create a. C and B. C2 files under test, and create SA. C and SB. C2 files under sub directory.

Create a simple makefile
Src = $ (wildcard *. C./SUB/*. c)
Dir = $ (notdir $ (SRC ))
OBJ = $ (patsubst %. C, %. O, $ (DIR ))

ALL:
@ Echo $ (SRC)
@ Echo $ (DIR)
@ Echo $ (OBJ)
@ Echo "end"
 
Result Analysis:
First line output:
A. c B. C./SUB/SA. C./SUB/SB. c

Wildcard expands all files with the suffix C under the specified directory./And./SUB.

Output in the second row:
A. c B. C SA. c sb. c
Notdir removes the path information from the expanded File

Output in the third row:
A. o B. O SA. O Sb. o

In $ (patsubst %. C, %. O, $ (DIR), patsubst replaces all variables in $ (DIR) with. O whose suffix is. C,
Any output.
Or you can use
OBJ = $ (DIR: %. c = %. O)
The same is true.

Here, the replacement reference rule in makefile is used to replace another variable with the variable you specified.
Its standard format is
$ (VaR: A = B) or $ {var: a = B}
It means to replace a with B at the end of each value in the VaR variable.