Red Hat ENTERPRISE LINUX 3 - DEVELOPER TOOLS GUIDE Instrukcja Użytkownika Pobierz pdf (Strona 13)

Chapter 2. Basic Principles of the Tools 9

target is usually the name of a ﬁle that a program generates; examples of targets are executable or

object ﬁles. A target can also be the name of an action to carry out, such as with the clean command (a

command that, deletes all ﬁles from a build directory before building). A dependency is a ﬁle that

is used as input to create the target. A target often depends on several ﬁles. command is activated by

make wnen dependancy has changed. A rule may have more than one command, with each command

on its own line. Usually a command is in a rule with dependencies and serves to create a target ﬁle if

any dependencies change. However, the rule that speciﬁes commands for the target does not require

dependencies; for instance, the rule containing the delete command that associates with the target,

clean, does not have dependencies. make activates commands on the dependencies to create or to

update the target. A rule can also explain how and when to activate a command. A makefile can

contain other text besides rules; a simple makefile requires only rules. Rules generally follow the

same pattern.

Note that every command line in a makefile must begin with a tab character.

2.10.1. Example Makefile

edit : main.o kbd.o command.o display.o insert.o search.o \

files.o utils.o

cc -o edit main.o kbd.o command.o display.o insert.o \

search.o files.o utils.o

main.o : main.c defs.h

cc -c main.c

kbd.o : kbd.c defs.h command.h

cc -c kbd.c

command.o : command.c defs.h command.h

cc -c command.c

display.o : display.c defs.h buffer.h

cc -c display.c

insert.o : insert.c defs.h buffer.h

cc -c insert.c

search.o : search.c defs.h buffer.h

cc -c search.c

files.o : files.c defs.h buffer.h command.h

cc -c files.c

utils.o : utils.c defs.h

cc -c utils.c

clean :

rm edit main.o kbd.o command.o display.o insert.o \

search.o files.o utils.o

The targets in the example makefile include the executable ﬁle, edit, and the main.o and kbd.o

object ﬁles. main.c and defs.h are the dependency ﬁles. Each .o ﬁle is both a target and a depen-

dency. When a target is a ﬁle, it needs to be recompiled or relinked if any of its dependencies change.

You must ﬁrst update any dependencies that automatically generate. In the example Makefile, edit

depends on eight object ﬁles; the object ﬁle, main.o, depends on the source ﬁle, main.c, and on

the defs.h header ﬁle. A shell command follows each line that contains a target and dependencies,

saying how to update the target ﬁle; a tab character must come at the beginning of every command line

to distinguish command lines from other lines in the makefile. make does not know anything about

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