The following is an example
of defining a canned sequence of commands.
run-yacc is the name of the variable being defined; endef marks the end of the definition; the lines in between are the commands. The define directive does not expand variable references and function calls in the canned sequence; the $ characters, parentheses, variable names, and so on, all become part of the value of the variable you are defining. See Defining variables verbatim for a complete explanation of define.
The first command in this example runs Yacc on the first dependency of whichever rule uses the canned sequence. The output file from Yacc is always named y.tab.c. The second command moves the output to the rules target file name.
To use the canned sequence,
substitute the variable into the commands of a rule. You can substitute
it like any other variable (see Basics
of variable references). Because variables defined by define
are recursively expanded variables, all the variable references you wrote
inside the define
are expanded now. Use the following for example.
foo.y will be substituted for the variable $ when it occurs in run-yaccs value, and foo.c for $@. This is a realistic example, but this particular one is not needed in practice because make has an implicit rule to figure out these commands based on the file names involved (see Using implicit rules).
In command execution, each line of a canned sequence is treated just as if the line appeared on its own in the rule, preceded by a tab. In particular, make invokes a separate subshell for each line.
You can use the special prefix characters that affect command lines (@, -, and +) on each line of a canned sequence. See Writing the commands in rules.
For instance, use the following
example of a canned sequence.
make
will not echo the first line, the echo
command. But it will echo the following two command lines. On the other
hand, prefix characters on the command line that refers to a canned sequence
apply to every line in the sequence. So the following rule statement does
not echo any commands. (See Command
echoing for a full explanation of @.)