Книга: Fedora™ Unleashed, 2008 edition

Building Programs with make

Building Programs with make

You use the make command to automatically build and install a C program, and for that use it is an easy tool. If you want to create your own automated builds, however, you need to learn the special syntax that make uses; the following sections walk you through a basic make setup.

The make command automatically builds and updates applications by using a makefile. A makefile is a text file that contains instructions about which options to pass on to the compiler preprocessor, the compiler, the assembler, and the linker. The makefile also specifies, among other things, which source code files have to be compiled (and the compiler command line) for a particular code module and which code modules are required to build the program — a mechanism called dependency checking.

The beauty of the make command is its flexibility. You can use make with a simple makefile, or you can write complex makefiles that contain numerous macros, rules, or commands that work in a single directory or traverse your file system recursively to build programs, update your system, and even function as document management systems. The make command works with nearly any program, including text processing systems such as TeX.

You could use make to compile, build, and install a software package, using a simple command like this:

# make install

You can use the default makefile (usually called Makefile, with a capital M), or you can use make's -f option to specify any makefile, such as MyMakeFile, like this:

# make -f MyMakeFile

Other options might be available, depending on the contents of your makefile.

Using make with macros can make a program portable. Macros enable users of other operating systems to easily configure a program build by specifying local values, such as the names and locations, or pathnames, of any required software tools. In the following example, macros define the name of the compiler (CC), the installer program (INS), where the program should be installed (INSDIR), where the linker should look for required libraries (LIBDIR), the names of required libraries (LIBS), a source code file (SRC), the intermediate object code file (OBS), and the name of the final program (PROG):

# a sample makefile for a skeleton program
CC= gcc
INS= install
INSDIR= /usr/local/bin
LIBDIR= -L/usr/X11R6/lib
LIBS= -lXm -lSM -lICE -lXt -lX11
SRC= skel.c
OBJS= skel.o
PROG= skel
skel: ${OBJS}
${CC} -o ${PROG} ${SRC} ${LIBDIR} ${LIBS}
install: ${PROG}
${INS} -g root -o root ${PROG} ${INSDIR}

Using the makefile from the preceding example, you can build a program like this:

# make

To build a specified component of a makefile, you can use a target definition on the command line. To build just the program, you use make with the skel target, like this:

# make skel

If you make any changes to any element of a target object, such as a source code file, make rebuilds the target automatically. This feature is part of the convenience of using make to manage a development project. To build and install a program in one step, you can specify the target of install like this:

#  make install

Larger software projects might have a number of traditional targets in the makefile, such as the following:

? test — To run specific tests on the final software

? man — To process an include or a troff document with the man macros

? clean — To delete any remaining object files

? archive — To clean up, archive, and compress the entire source code tree

? bugreport — To automatically collect and then mail a copy of the build or error logs

Large applications can require hundreds of source code files. Compiling and linking these applications can be a complex and error-prone task. The make utility helps you organize the process of building the executable form of a complex application from many source files.

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