make gets a fatal signal while a command is executing, it may
delete the target file that the command 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
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
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
.PRECIOUS depend on it. Before remaking a target,
make checks to see whether it appears on the dependencies 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.
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