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Make command

Not only can the macro definition appear after the linux make command, but it can also be followed by other command-line arguments that specify the target file that needs to be compiled. Its standard form is:

Target1 [target2...] [:] [dependent1...] [; commands] [#...]

[(tab) commands] [#...]

The middle part of the square brackets indicates that it is optional. Targets and dependents can contain characters, numbers, periods, and "/" symbols. Except for references, commands cannot contain "#" and line breaks are not allowed.

In general, there is only one ":" in the command line argument, and the command sequence is usually related to the description lines that define the dependencies between files in the makefile file. If the description lines associated with the target specify the relevant command sequence, the relevant command commands are executed, even though the aommand field after the semicolon and (tab) may even be NULL. If the lines associated with the target do not specify command, the system's default target file generation rules are invoked.

If the command line argument contains two colons "::", the command sequence at this time may be related to all the lines in makefile that describe file dependencies. The relevant commands pointed to by the description lines associated with the target are executed. The build-in rules will also be enforced. If a non-"0" error signal is returned during the execution of the command command, such as an incorrect target file name in the makefile file or a command string that begins with a hyphen, the make operation usually terminates, but if the make is followed by a "- I" parameter, make ignores such error signals. The Make life itself can take four parameters: flag, macro definition, description file name, and target file name. Its standard form is:

Make [flags] [macro definitions] [targets]

Under Unix system, the flag bit flags option and its meaning are:

◆-f file specifies the file file as the description file, and if the file parameter is a "-" character, then the description file points to standard input. If there is no "- f" parameter, the system defaults to a file named makefile or Makefile in the current directory as a description file. In linux, the GNUmake tool searches for makefile files in the current working directory in the order of GNUmakefile, makefile, and Makefile.

◆-I ignores the error message returned by the command execution.

◆-s silent mode, does not output the corresponding command line information before execution.

◆-r prohibits the use of build-in rules.

◆-n non-execution mode, outputs all execution commands, but does not execute.

◆-t updates the target file.

The ◆-Q make operation returns "0" or non-"0" status information based on whether the target file has been updated.

◆-p outputs all macro definitions and object file descriptions.

◆-d Debug mode, which outputs detailed information about the file and the test time.

The common options for make flag bits under linux are slightly different from those in Unix systems. We only list the different parts below:

◆-c dir changes to the specified directory dir before reading makefile.

◆-I dir uses this option to specify a search directory when it contains other makefile files.

◆-h help document, showing all make options.

◆-w displays the working directory before and after processing the makefile.

Through the target in the command line argument, you can specify the targets to be compiled by make and allow you to define multiple targets to compile at the same time, compiling the target files specified in the target options in sequence from left to right. If no destination is specified on the command line, the system default target points to * target files in the description file.

Typically, a clean target is also defined in makefile, which can be used to clean up intermediate files during compilation, such as:

Clean:

Rm-f * .o

When you run make clean, the rm-f * .o command is executed, resulting in the deletion of all intermediate files generated during compilation.

Implied rule

The make tool contains built-in or implicit rules that define how to build specific types of targets from different dependent files. Unix systems usually support an implicit rule based on a file extension, that is, a file name suffix. This suffix rule defines how to convert a file with a specific file name suffix (for example, .c file) to a file with another file name suffix (for example, .o file):

.c: .o

$(CC) $(CFLAGS) $(CPPFLAGS)-c-o $@ $

< 系统中默认的常用文件扩展名及其含义为： ◆.o 目标文件 ◆.c C源文件 ◆.f FORTRAN源文件 ◆.s 汇编源文件 ◆.y Yacc-C源语法 ◆.l Lex源语法 在早期的Unix系统系统中还支持Yacc-C源语法和Lex源语法。在编译过程中，系统会首先在makefile文件中寻找与目标文件相关的.C文件，如果还有与之相依赖的.y和.l文件，则首先将其转换为.c文件后再编译生成相应的.o文件；如果没有与目标相关的.c文件而只有相关的.y文件，则系统将直接编译.y文件。 而GNU make 除了支持后缀规则外还支持另一种类型的隐含规则--模式规则。这种规则更加通用，因为可以利用模式规则定义更加复杂的依赖性规则。模式规则看起来非常类似于正则规则，但在目标名称的前面多了一个 % 号，同时可用来定义目标和依赖文件之间的关系，例如下面的模式规则定义了如何将任意一个 file.c 文件转换为 file.o 文件： %.c:%.o $(CC) $(CFLAGS) $(CPPFLAGS) -c -o $@ $< #EXAMPLE# 下面将给出一个较为全面的示例来对makefile文件和make命令的执行进行进一步的说明，其中make命令不仅涉及到了C源文件还包括了Yacc 语法。本例选自"Unix Programmer's Manual 7th Edition, Volume 2A" Page 283-284 下面是描述文件的具体内容： #Description file for the Make command #Send to print P=und -3 | opr -r2 #The source files that are needed by object files FILES= Makefile version.c defs main.c donamc.c misc.c file.c dosys.c gram.y lex.c gcos.c #The definitions of object files OBJECTS= vesion.o main.o donamc.o misc.o file.o dosys.o gram.o LIBES= -LS LINT= lnit -p CFLAGS= -O make: $(OBJECTS) cc $(CFLAGS) $(OBJECTS) $(LIBES) -o make size make $(OBJECTS): defs gram.o: lex.c cleanup: -rm *.o gram.c install: @size make /usr/bin/make cp make /usr/bin/make ; rm make #print recently changed files print: $(FILES) pr $? | $P touch print test: make -dp | grep -v TIME>

1zap

/ usr/bin/make-dp | grep-v TIME > 2zap

Diff 1zap 2zap

Rm 1zap 2zap

Lint: dosys.c donamc.c file.c main.c misc.c version.c gram.c

$(LINT) dosys.c donamc.c file.c main.c misc.c version.c

Gram.c

Rm gram.c

Arch:

Ar uv / sys/source/s2/make.a $(FILES)

Typically, the command that requires the output to be executed should be defined in the description file as above. After executing the linux make command, the output is as follows:

$make

Cc-c version.c

Cc-c main.c

Cc-c donamc.c

Cc-c misc.c

Cc-c file.c

Cc-c dosys.c

Yacc gram.y

Mv y.tab.c gram.c

Cc-c gram.c

Cc version.o main.o donamc.o misc.o file.o dosys.o gram.o

-LS-o make

13188+3348+3044=19580b=046174b

The digital information of * * is the output of the "@ size make" command. The reason why there is only output without a corresponding command line is because the "@ size make" command starts with "@", and this symbol forbids printing out the command line on which it is located.

Several command lines in the description file are useful in maintaining compilation information. The function of the "print" command line is to print out all the file names that have changed since the last "make print" command. The system uses a 0-byte file named print to determine when the print command is executed, and the macro $? Then point to the file names of those files that have been modified after the print file has been changed. If you want to specify that the output is sent to a specified file after the print command is executed, you can modify the macro definition of P:

Make print "P = cat > zap"

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