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<h1 id="make1"><a class="header" href="#make1">make(1)</a></h1>
<h2 id="anatomy-of-make-rules"><a class="header" href="#anatomy-of-make-rules">Anatomy of <code>make</code> rules</a></h2>
<pre><code class="language-make">target .. : prerequisite ..
recipe
..
</code></pre>
<ul>
<li><code>target</code>: an output generated by the rule</li>
<li><code>prerequisite</code>: an input that is used to generate the target</li>
<li><code>recipe</code>: list of actions to generate the output from the input</li>
</ul>
<blockquote>
<p>Use <code>make -p</code> to print all rules and variables (implicitly + explicitly defined).</p>
</blockquote>
<h2 id="pattern-rules--variables"><a class="header" href="#pattern-rules--variables">Pattern rules & variables</a></h2>
<h3 id="pattern-rules"><a class="header" href="#pattern-rules">Pattern rules</a></h3>
<p>A pattern rule contains the <code>%</code> char (exactly one of them) and look like this example:</p>
<pre><code class="language-make">%.o : %.c
$(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@
</code></pre>
<p>The target matches files of the pattern <code>%.o</code>, where <code>%</code> matches any none-empty
substring and other character match just them self.</p>
<p>The substring matched by <code>%</code> is called the <code>stem</code>.</p>
<p><code>%</code> in the prerequisite stands for the matched <code>stem</code> in the target.</p>
<h3 id="automatic-variables"><a class="header" href="#automatic-variables">Automatic variables</a></h3>
<p>As targets and prerequisites in pattern rules can't be spelled explicitly in
the recipe, make provides a set of automatic variables to work with:</p>
<ul>
<li><code>$@</code>: Name of the target that triggered the rule.</li>
<li><code>$<</code>: Name of the first prerequisite.</li>
<li><code>$^</code>: Names of all prerequisites (without duplicates).</li>
<li><code>$+</code>: Names of all prerequisites (with duplicates).</li>
<li><code>$*</code>: Stem of the pattern rule.</li>
</ul>
<pre><code class="language-make"># file: Makefile
all: foobar blabla
foo% bla%: aaa bbb bbb
@echo "@ = $@"
@echo "< = $<"
@echo "^ = $^"
@echo "+ = $+"
@echo "* = $*"
@echo "----"
aaa:
bbb:
</code></pre>
<p>Running above <code>Makefile</code> gives:</p>
<pre><code class="language-text">@ = foobar
< = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bar
----
@ = blabla
< = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bla
----
</code></pre>
<p>Variables related to filesystem paths:</p>
<ul>
<li><code>$(CURDIR)</code>: Path of current working dir after using <code>make -C path</code></li>
</ul>
<h3 id="multi-line-variables"><a class="header" href="#multi-line-variables">Multi-line variables</a></h3>
<pre><code class="language-make">define my_var
@echo foo
@echo bar
endef
all:
$(my_var)
</code></pre>
<p>Running above <code>Makefile</code> gives:</p>
<pre><code class="language-text">foo
bar
</code></pre>
<h2 id="arguments"><a class="header" href="#arguments">Arguments</a></h2>
<p>Arguments specified on the command line <em>override</em> ordinary variable
assignments in the makefile (<a href="https://www.gnu.org/software/make/manual/html_node/Overriding.html">overriding variables</a>).</p>
<pre><code class="language-make">VAR = abc
all:
@echo VAR=$(VAR)
</code></pre>
<pre><code class="language-text"># make
VAR=abc
# make VAR=123
VAR=123
</code></pre>
<h2 id="useful-functions"><a class="header" href="#useful-functions">Useful functions</a></h2>
<h3 id="substitution-references"><a class="header" href="#substitution-references">Substitution references</a></h3>
<p>Substitute strings matching pattern in a list.</p>
<pre><code class="language-make">in := a.o l.a c.o
out := $(in:.o=.c)
# => out = a.c l.a c.c
</code></pre>
<h3 id="patsubst-ref"><a class="header" href="#patsubst-ref"><code>patsubst</code> (<a href="https://www.gnu.org/software/make/manual/html_node/Text-Functions.html#index-patsubst-1">ref</a>)</a></h3>
<pre><code class="language-make">in := a.c b.c
out := $(patsubst %.c, build/%.o, $(in))
# => out = build/a.o build/b.o
# This is actually equivalent to $(in:%.c=build/%.o)
</code></pre>
<h3 id="filter"><a class="header" href="#filter"><code>filter</code></a></h3>
<p>Keep strings matching a pattern in a list.</p>
<pre><code class="language-make">in := a.a b.b c.c d.d
out := $(filter %.b %.c, $(in))
# => out = b.b c.c
</code></pre>
<h3 id="filter-out"><a class="header" href="#filter-out"><code>filter-out</code></a></h3>
<p>Remove strings matching a pattern from a list.</p>
<pre><code class="language-make">in := a.a b.b c.c d.d
out := $(filter-out %.b %.c, $(in))
# => out = a.a d.d
</code></pre>
<h3 id="abspath"><a class="header" href="#abspath"><code>abspath</code></a></h3>
<p>Resolve each file name as absolute path (don't resolve symlinks).</p>
<pre><code class="language-make">$(abspath fname1 fname2 ..)
</code></pre>
<h3 id="realpath"><a class="header" href="#realpath"><code>realpath</code></a></h3>
<p>Resolve each file name as canonical path.</p>
<pre><code class="language-make">$(realpath fname1 fname2 ..)
</code></pre>
<h3 id="call--ref"><a class="header" href="#call--ref"><code>call</code> (<a href="https://www.gnu.org/software/make/manual/html_node/Call-Function.html">ref</a>)</a></h3>
<p>Invoke parametrized function, which is an expression saved in a variable.</p>
<pre><code class="language-make">swap = $(2) $(1)
all:
@echo "call swap first second -> $(call swap,first,second)"
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">call swap first second -> second first
</code></pre>
<h3 id="eval-ref"><a class="header" href="#eval-ref"><code>eval</code> (<a href="https://www.gnu.org/software/make/manual/html_node/Eval-Function.html">ref</a>)</a></h3>
<p>Allows to define new makefile constructs by evaluating the result of a variable
or function.</p>
<pre><code class="language-make">define new_rule
$(1):
@echo "$(1) -> $(2)"
endef
default: rule1 rule2
$(eval $(call new_rule,rule1,foo))
$(eval $(call new_rule,rule2,bar))
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">rule1 -> foo
rule2 -> bar
</code></pre>
<h3 id="foreach-ref"><a class="header" href="#foreach-ref">foreach (<a href="https://www.gnu.org/software/make/manual/html_node/Foreach-Function.html">ref</a>)</a></h3>
<p>Repeat a piece of text for a list of values, given the syntax <code>$(foreach var,list,text)</code>.</p>
<pre><code class="language-make">myfn = x$(1)x
default:
@echo $(foreach V,foo bar baz,$(call myfn,$(V)))
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">xfoox xbarx xbazx
</code></pre>
<h2 id="examples"><a class="header" href="#examples">Examples</a></h2>
<h3 id="config-based-settings"><a class="header" href="#config-based-settings">Config based settings</a></h3>
<pre><code class="language-make">conf-y := default
conf-$(FOO) := $(conf-y) foo
conf-$(BAR) := $(conf-y) bar
libs-y := libdef
libs-$(FOO) += libfoo
libs-$(BAR) += libbar
all:
@echo "conf-y: $(conf-y)"
@echo "libs-y: $(libs-y)"
</code></pre>
<p>Yields the following results.</p>
<pre><code class="language-sh">$ make
conf-y: default
libs-y: libdef
$ make FOO=y
conf-y: default foo
libs-y: libdef libfoo
$ make BAR=y
conf-y: default bar
libs-y: libdef libbar
$ make FOO=y BAR=y
conf-y: default foo bar
libs-y: libdef libfoo libbar
</code></pre>
<h3 id="using-foreach--eval--call-to-generate-new-rules"><a class="header" href="#using-foreach--eval--call-to-generate-new-rules">Using <code>foreach / eval / call</code> to generate new rules</a></h3>
<pre><code class="language-make">define new_rule
$(1):
@echo "$(1) -> $(2)"
endef
arg-rule1 = foo
arg-rule2 = bar
RULES = rule1 rule2
all: $(RULES)
$(foreach R,$(RULES),$(eval $(call new_rule,$(R),$(arg-$(R)))))
# equivalent to
# $(eval $(call new_rule,rule1,foo))
# $(eval $(call new_rule,rule2,bar))
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">rule1 -> foo
rule2 -> bar
</code></pre>
<blockquote>
<p>Use <code>make -R -p</code> to print the make database including the rules.</p>
</blockquote>
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