make: Errors
5.5 Errors in Recipes
=====================
After each shell invocation returns, 'make' looks at its exit status.
If the shell completed successfully (the exit status is zero), the next
line in the recipe is executed in a new shell; after the last line is
finished, the rule is finished.
If there is an error (the exit status is nonzero), 'make' gives up on
the current rule, and perhaps on all rules.
Sometimes the failure of a certain recipe line does not indicate a
problem. For example, you may use the 'mkdir' command to ensure that a
directory exists. If the directory already exists, 'mkdir' will report
an error, but you probably want 'make' to continue regardless.
To ignore errors in a recipe line, write a '-' at the beginning of
the line's text (after the initial tab). The '-' is discarded before
the line is passed to the shell for execution.
For example,
clean:
-rm -f *.o
This causes 'make' to continue even if 'rm' is unable to remove a file.
When you run 'make' with the '-i' or '--ignore-errors' flag, errors
are ignored in all recipes of all rules. A rule in the makefile for the
special target '.IGNORE' has the same effect, if there are no
prerequisites. These ways of ignoring errors are obsolete because '-'
is more flexible.
When errors are to be ignored, because of either a '-' or the '-i'
flag, 'make' treats an error return just like success, except that it
prints out a message that tells you the status code the shell exited
with, and says that the error has been ignored.
When an error happens that 'make' has not been told to ignore, it
implies that the current target cannot be correctly remade, and neither
can any other that depends on it 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. 
Summary of Options Options Summary.
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;
Interrupts. 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.
Info Catalog
make: Parallel
make: Recipes
make: Interrupts