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makefile Q about targets $@
09-18-2007
makefile Q about targets $@
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MAKE(1) General Commands Manual MAKE(1) NAME
make - maintain program groups SYNOPSIS
make [ -f makefile ] [ option ] ... file ... DESCRIPTION
Make executes commands in makefile to update one or more target names. Name is typically a program. If no -f option is present, `make- file' and `Makefile' are tried in order. If makefile is `-', the standard input is taken. More than one -f option may appear Make updates a target if it depends on prerequisite files that have been modified since the target was last modified, or if the target does not exist. Makefile contains a sequence of entries that specify dependencies. The first line of an entry is a blank-separated list of targets, then a colon, then a list of prerequisite files. Text following a semicolon, and all following lines that begin with a tab, are shell commands to be executed to update the target. Sharp and newline surround comments. The following makefile says that `pgm' depends on two files `a.o' and `b.o', and that they in turn depend on `.c' files and a common file `incl'. pgm: a.o b.o cc a.o b.o -lm -o pgm a.o: incl a.c cc -c a.c b.o: incl b.c cc -c b.c Makefile entries of the form string1 = string2 are macro definitions. Subsequent appearances of $(string1) are replaced by string2. If string1 is a single character, the parentheses are optional. Make infers prerequisites for files for which makefile gives no construction commands. For example, a `.c' file may be inferred as prereq- uisite for a `.o' file and be compiled to produce the `.o' file. Thus the preceding example can be done more briefly: pgm: a.o b.o cc a.o b.o -lm -o pgm a.o b.o: incl Prerequisites are inferred according to selected suffixes listed as the `prerequisites' for the special name `.SUFFIXES'; multiple lists accumulate; an empty list clears what came before. Order is significant; the first possible name for which both a file and a rule as described in the next paragraph exist is inferred. The default list is .SUFFIXES: .out .o .c .e .r .f .y .l .s The rule to create a file with suffix s2 that depends on a similarly named file with suffix s1 is specified as an entry for the `target' s1s2. In such an entry, the special macro $* stands for the target name with suffix deleted, $@ for the full target name, $< for the com- plete list of prerequisites, and $? for the list of prerequisites that are out of date. For example, a rule for making optimized `.o' files from `.c' files is .c.o: ; cc -c -O -o $@ $*.c Certain macros are used by the default inference rules to communicate optional arguments to any resulting compilations. In particular, `CFLAGS' is used for cc and f77(1) options, `LFLAGS' and `YFLAGS' for lex and yacc(1) options. Command lines are executed one at a time, each by its own shell. A line is printed when it is executed unless the special target `.SILENT' is in makefile, or the first character of the command is `@'. Commands returning nonzero status (see intro(1)) cause make to terminate unless the special target `.IGNORE' is in makefile or the command begins with <tab><hyphen>. Interrupt and quit cause the target to be deleted unless the target depends on the special name `.PRECIOUS'. Other options: -i Equivalent to the special entry `.IGNORE:'. -k When a command returns nonzero status, abandon work on the current entry, but continue on branches that do not depend on the current entry. -n Trace and print, but do not execute the commands needed to update the targets. -t Touch, i.e. update the modified date of targets, without executing any commands. -r Equivalent to an initial special entry `.SUFFIXES:' with no list. -s Equivalent to the special entry `.SILENT:'. FILES
makefile, Makefile SEE ALSO
sh(1), touch(1) S. I. Feldman Make - A Program for Maintaining Computer Programs BUGS
Some commands return nonzero status inappropriately. Use -i to overcome the difficulty. Commands that are directly executed by the shell, notably cd(1), are ineffectual across newlines in make. MAKE(1)