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9.3 Instead of Executing Recipes
The makefile tells make
how to tell whether a target is up to date,
and how to update each target. But updating the targets is not always
what you want. Certain options specify other activities for make
.
- ‘-n’
- ‘--just-print’
- ‘--dry-run’
- ‘--recon’
-
“No-op”. Causes
make
to print the recipes that are needed to make the targets up to date, but not actually execute them. Note that some recipes are still executed, even with this flag (see section How theMAKE
Variable Works). Also any recipes needed to update included makefiles are still executed (see section How Makefiles Are Remade). - ‘-t’
- ‘--touch’
-
“Touch”. Marks targets as up to date without actually changing them. In other words,
make
pretends to update the targets but does not really change their contents; instead only their modified times are updated. - ‘-q’
- ‘--question’
-
“Question”. Silently check whether the targets are up to date, but do not execute recipes; the exit code shows whether any updates are needed.
- ‘-W file’
- ‘--what-if=file’
- ‘--assume-new=file’
- ‘--new-file=file’
-
“What if”. Each ‘-W’ flag is followed by a file name. The given files’ modification times are recorded by
make
as being the present time, although the actual modification times remain the same. You can use the ‘-W’ flag in conjunction with the ‘-n’ flag to see what would happen if you were to modify specific files.
With the ‘-n’ flag, make
prints the recipe that it would
normally execute but usually does not execute it.
With the ‘-t’ flag, make
ignores the recipes in the rules
and uses (in effect) the command touch
for each target that needs to
be remade. The touch
command is also printed, unless ‘-s’ or
.SILENT
is used. For speed, make
does not actually invoke
the program touch
. It does the work directly.
With the ‘-q’ flag, make
prints nothing and executes no
recipes, but the exit status code it returns is zero if and only if the
targets to be considered are already up to date. If the exit status is
one, then some updating needs to be done. If make
encounters an
error, the exit status is two, so you can distinguish an error from a
target that is not up to date.
It is an error to use more than one of these three flags in the same
invocation of make
.
The ‘-n’, ‘-t’, and ‘-q’ options do not affect recipe
lines that begin with ‘+’ characters or contain the strings
‘$(MAKE)’ or ‘${MAKE}’. Note that only the line containing
the ‘+’ character or the strings ‘$(MAKE)’ or ‘${MAKE}’
is run regardless of these options. Other lines in the same rule are
not run unless they too begin with ‘+’ or contain ‘$(MAKE)’ or
‘${MAKE}’ (See section How the MAKE
Variable Works.)
The ‘-t’ flag prevents phony targets (see section Phony Targets) from being updated, unless there are recipe lines beginning with ‘+’ or containing ‘$(MAKE)’ or ‘${MAKE}’.
The ‘-W’ flag provides two features:
-
If you also use the ‘-n’ or ‘-q’ flag, you can see what
make
would do if you were to modify some files. -
Without the ‘-n’ or ‘-q’ flag, when
make
is actually executing recipes, the ‘-W’ flag can directmake
to act as if some files had been modified, without actually running the recipes for those files.
Note that the options ‘-p’ and ‘-v’ allow you to obtain other
information about make
or about the makefiles in use
(see section Summary of Options).
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