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These functions control the way make runs. Generally, they are used to provide information to the user of the makefile or to cause make to stop if some sort of environmental error is detected.
$(error text...)
For example,
ifdef ERROR1 $(error error is $(ERROR1)) endif |
will generate a fatal error during the read of the makefile if the
make
variable ERROR1
is defined. Or,
ERR = $(error found an error!) .PHONY: err err: ; $(ERR) |
will generate a fatal error while make
is running, if the
err
target is invoked.
$(warning text...)
error
function, above,
except that make
doesn't exit. Instead, text is expanded
and the resulting message is displayed, but processing of the makefile
continues.
The result of the expansion of this function is the empty string.