5.5 Errors in Commands
After each shell command returns, `make' looks at its exit status. If
the command completed successfully, the next command line is executed
in a new shell; after the last command line is finished, the rule is
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 command 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 command line, write a `-' at the beginning of
the line's text (after the initial tab). The `-' is discarded before
the command is passed to the shell for execution.
-rm -f *.o
This causes `rm' to continue even if it is unable to remove a file.
When you run `make' with the `-i' or `--ignore-errors' flag, errors
are ignored in all commands 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 command 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 commands 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 command 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 command is killed by a
signal; Interrupts. So generally the right thing to do is to
delete the target file if the command 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
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