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50 GNU make

either directly or indirectly. No further recipes will be executed for these targets, since their

preconditions have not been achieved.

Normally make gives up immediately in this circumstance, returning a nonzero status.

However, if the ‘-k’ or ‘--keep-going’ ﬂag is speciﬁed, make continues to consider the

other prerequisites of the pending targets, remaking them if necessary, before it gives up

and returns nonzero status. For example, after an error in compiling one object ﬁle, ‘make

-k’ will continue compiling other object ﬁles even though it already knows that linking them

will be impossible. See Section 9.7 [Summary of Options], page 104.

The usual behavior assumes that your purpose is to get the speciﬁed targets up to date;

once make learns that this is impossible, it might as well report the failure immediately.

The ‘-k’ option says that the real purpose is to test as many of the changes made in the

program as possible, perhaps to ﬁnd several independent problems so that you can correct

them all before the next attempt to compile. This is why Emacs’ compile command passes

the ‘-k’ ﬂag by default.

Usually when a recipe line fails, if it has changed the target ﬁle at all, the ﬁle is corrupted

and cannot be used—or at least it is not completely updated. Yet the ﬁle’s time stamp says

that it is now up to date, so the next time make runs, it will not try to update that ﬁle. The

situation is just the same as when the shell is killed by a signal; see Section 5.6 [Interrupts],

page 50. So generally the right thing to do is to delete the target ﬁle if the recipe fails after

beginning to change the ﬁle. make will do this if .DELETE_ON_ERROR appears as a target.

This is almost always what you want make to do, but it is not historical practice; so for

compatibility, you must explicitly request it.

5.6 Interrupting or Killing make

If make gets a fatal signal while a shell is executing, it may delete the target ﬁle that the

recipe was supposed to update. This is done if the target ﬁle’s last-modiﬁcation time has

changed since make ﬁrst checked it.

The purpose of deleting the target is to make sure that it is remade from scratch when

make is next run. Why is this? Suppose you type Ctrl-c while a compiler is running, and

it has begun to write an object ﬁle foo.o. The Ctrl-c kills the compiler, resulting in an

incomplete ﬁle whose last-modiﬁcation time is newer than the source ﬁle foo.c. But make

also receives the Ctrl-c signal and deletes this incomplete ﬁle. If make did not do this, the

next invocation of make would think that foo.o did not require updating—resulting in a

strange error message from the linker when it tries to link an object ﬁle half of which is

missing.

You can prevent the deletion of a target ﬁle in this way by making the special target

.PRECIOUS depend on it. Before remaking a target, make checks to see whether it appears

on the prerequisites of .PRECIOUS, and thereby decides whether the target should be deleted

if a signal happens. Some reasons why you might do this are that the target is updated

in some atomic fashion, or exists only to record a modiﬁcation-time (its contents do not

matter), or must exist at all times to prevent other sorts of trouble.

5.7 Recursive Use of make

Recursive use of make means using make as a command in a makeﬁle. This technique

is useful when you want separate makeﬁles for various subsystems that compose a larger

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