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                <ol class="chapter"><li class="chapter-item expanded affix "><a href="../intro.html">Introduction</a></li><li class="chapter-item expanded "><a href="../tools/index.html"><strong aria-hidden="true">1.</strong> Tools</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../tools/zsh.html"><strong aria-hidden="true">1.1.</strong> zsh</a></li><li class="chapter-item expanded "><a href="../tools/bash.html"><strong aria-hidden="true">1.2.</strong> bash</a></li><li class="chapter-item expanded "><a href="../tools/fish.html"><strong aria-hidden="true">1.3.</strong> fish</a></li><li class="chapter-item expanded "><a href="../tools/tmux.html"><strong aria-hidden="true">1.4.</strong> tmux</a></li><li class="chapter-item expanded "><a href="../tools/git.html"><strong aria-hidden="true">1.5.</strong> git</a></li><li class="chapter-item expanded "><a href="../tools/awk.html"><strong aria-hidden="true">1.6.</strong> awk</a></li><li class="chapter-item expanded "><a href="../tools/emacs.html"><strong aria-hidden="true">1.7.</strong> emacs</a></li><li class="chapter-item expanded "><a href="../tools/gpg.html"><strong aria-hidden="true">1.8.</strong> gpg</a></li><li class="chapter-item expanded "><a href="../tools/gdb.html"><strong aria-hidden="true">1.9.</strong> gdb</a></li><li class="chapter-item expanded "><a href="../tools/gdbserver.html"><strong aria-hidden="true">1.10.</strong> gdbserver</a></li><li class="chapter-item expanded "><a href="../tools/radare2.html"><strong aria-hidden="true">1.11.</strong> radare2</a></li><li class="chapter-item expanded "><a href="../tools/qemu.html"><strong aria-hidden="true">1.12.</strong> qemu</a></li><li class="chapter-item expanded "><a href="../tools/pacman.html"><strong aria-hidden="true">1.13.</strong> pacman</a></li><li class="chapter-item expanded "><a href="../tools/dot.html"><strong aria-hidden="true">1.14.</strong> dot</a></li><li class="chapter-item expanded "><a href="../tools/ffmpeg.html"><strong aria-hidden="true">1.15.</strong> ffmpeg</a></li><li class="chapter-item expanded "><a href="../tools/column.html"><strong aria-hidden="true">1.16.</strong> column</a></li><li class="chapter-item expanded "><a href="../tools/sort.html"><strong aria-hidden="true">1.17.</strong> sort</a></li><li class="chapter-item expanded "><a href="../tools/sed.html"><strong aria-hidden="true">1.18.</strong> sed</a></li><li class="chapter-item expanded "><a href="../tools/gnuplot.html"><strong aria-hidden="true">1.19.</strong> gnuplot</a></li></ol></li><li class="chapter-item expanded "><a href="../monitor/index.html"><strong aria-hidden="true">2.</strong> Resource analysis & monitor</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../monitor/lsof.html"><strong aria-hidden="true">2.1.</strong> lsof</a></li><li class="chapter-item expanded "><a href="../monitor/ss.html"><strong aria-hidden="true">2.2.</strong> ss</a></li><li class="chapter-item expanded "><a href="../monitor/pidstat.html"><strong aria-hidden="true">2.3.</strong> pidstat</a></li><li class="chapter-item expanded "><a href="../monitor/pgrep.html"><strong aria-hidden="true">2.4.</strong> pgrep</a></li><li class="chapter-item expanded "><a href="../monitor/ps.html"><strong aria-hidden="true">2.5.</strong> ps</a></li><li class="chapter-item expanded "><a href="../monitor/pmap.html"><strong aria-hidden="true">2.6.</strong> pmap</a></li><li class="chapter-item expanded "><a href="../monitor/pstack.html"><strong aria-hidden="true">2.7.</strong> pstack</a></li></ol></li><li class="chapter-item expanded "><a href="../trace_profile/index.html"><strong aria-hidden="true">3.</strong> Trace and Profile</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../trace_profile/time.html"><strong aria-hidden="true">3.1.</strong> time</a></li><li class="chapter-item expanded "><a href="../trace_profile/strace.html"><strong aria-hidden="true">3.2.</strong> strace</a></li><li class="chapter-item expanded "><a href="../trace_profile/ltrace.html"><strong aria-hidden="true">3.3.</strong> ltrace</a></li><li class="chapter-item expanded "><a href="../trace_profile/perf.html"><strong aria-hidden="true">3.4.</strong> perf</a></li><li class="chapter-item expanded "><a href="../trace_profile/oprofile.html"><strong aria-hidden="true">3.5.</strong> OProfile</a></li><li class="chapter-item expanded "><a href="../trace_profile/callgrind.html"><strong aria-hidden="true">3.6.</strong> callgrind</a></li></ol></li><li class="chapter-item expanded "><a href="../binary/index.html"><strong aria-hidden="true">4.</strong> Binary</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binary/od.html"><strong aria-hidden="true">4.1.</strong> od</a></li><li class="chapter-item expanded "><a href="../binary/xxd.html"><strong aria-hidden="true">4.2.</strong> xxd</a></li><li class="chapter-item expanded "><a href="../binary/readelf.html"><strong aria-hidden="true">4.3.</strong> readelf</a></li><li class="chapter-item expanded "><a href="../binary/objdump.html"><strong aria-hidden="true">4.4.</strong> objdump</a></li><li class="chapter-item expanded "><a href="../binary/nm.html"><strong aria-hidden="true">4.5.</strong> nm</a></li></ol></li><li class="chapter-item expanded "><a href="../development/index.html"><strong aria-hidden="true">5.</strong> Development</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/c++filt.html"><strong aria-hidden="true">5.1.</strong> c++filt</a></li><li class="chapter-item expanded "><a href="../development/c++.html"><strong aria-hidden="true">5.2.</strong> c++</a></li><li class="chapter-item expanded "><a href="../development/glibc.html"><strong aria-hidden="true">5.3.</strong> glibc</a></li><li class="chapter-item expanded "><a href="../development/gcc.html"><strong aria-hidden="true">5.4.</strong> gcc</a></li><li class="chapter-item expanded "><a href="../development/cmake.html"><strong aria-hidden="true">5.5.</strong> cmake</a></li><li class="chapter-item expanded "><a href="../development/make.html" class="active"><strong aria-hidden="true">5.6.</strong> make</a></li><li class="chapter-item expanded "><a href="../development/ld.so.html"><strong aria-hidden="true">5.7.</strong> ld.so</a></li><li class="chapter-item expanded "><a href="../development/symbolver.html"><strong aria-hidden="true">5.8.</strong> symbol versioning</a></li><li class="chapter-item expanded "><a href="../development/python.html"><strong aria-hidden="true">5.9.</strong> python</a></li><li class="chapter-item expanded "><a href="../development/gcov.html"><strong aria-hidden="true">5.10.</strong> gcov</a></li><li class="chapter-item expanded "><a href="../development/pgo.html"><strong aria-hidden="true">5.11.</strong> pgo</a></li></ol></li><li class="chapter-item expanded "><a href="../linux/index.html"><strong aria-hidden="true">6.</strong> Linux</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../linux/systemd.html"><strong aria-hidden="true">6.1.</strong> systemd</a></li><li class="chapter-item expanded "><a href="../linux/coredump.html"><strong aria-hidden="true">6.2.</strong> coredump</a></li><li class="chapter-item expanded "><a href="../linux/ptrace_scope.html"><strong aria-hidden="true">6.3.</strong> ptrace_scope</a></li><li class="chapter-item expanded "><a href="../linux/cryptsetup.html"><strong aria-hidden="true">6.4.</strong> cryptsetup</a></li><li class="chapter-item expanded "><a href="../linux/swap.html"><strong aria-hidden="true">6.5.</strong> swap</a></li><li class="chapter-item expanded "><a href="../linux/input.html"><strong aria-hidden="true">6.6.</strong> input</a></li><li class="chapter-item expanded "><a href="../linux/acl.html"><strong aria-hidden="true">6.7.</strong> acl</a></li><li class="chapter-item expanded "><a href="../linux/zfs.html"><strong aria-hidden="true">6.8.</strong> zfs</a></li></ol></li><li class="chapter-item expanded "><a href="../network/index.html"><strong aria-hidden="true">7.</strong> Network</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../network/tcpdump.html"><strong aria-hidden="true">7.1.</strong> tcpdump</a></li><li class="chapter-item expanded "><a href="../network/tshark.html"><strong aria-hidden="true">7.2.</strong> tshark</a></li><li class="chapter-item expanded "><a href="../network/firewall-cmd.html"><strong aria-hidden="true">7.3.</strong> firewall-cmd</a></li><li class="chapter-item expanded "><a href="../network/nftables.html"><strong aria-hidden="true">7.4.</strong> nftables</a></li></ol></li><li class="chapter-item expanded "><a href="../web/index.html"><strong aria-hidden="true">8.</strong> Web</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../web/html.html"><strong aria-hidden="true">8.1.</strong> html</a></li><li class="chapter-item expanded "><a href="../web/css.html"><strong aria-hidden="true">8.2.</strong> css</a></li><li class="chapter-item expanded "><a href="../web/chartjs.html"><strong aria-hidden="true">8.3.</strong> chartjs</a></li></ol></li><li class="chapter-item expanded "><a href="../arch/index.html"><strong aria-hidden="true">9.</strong> Arch</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../arch/x86_64.html"><strong aria-hidden="true">9.1.</strong> x86_64</a></li><li class="chapter-item expanded "><a href="../arch/arm64.html"><strong aria-hidden="true">9.2.</strong> arm64</a></li><li class="chapter-item expanded "><a href="../arch/armv7.html"><strong aria-hidden="true">9.3.</strong> armv7</a></li><li class="chapter-item expanded "><a href="../arch/riscv.html"><strong aria-hidden="true">9.4.</strong> riscv</a></li></ol></li></ol>
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                    <h1 class="menu-title">Notes</h1>

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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 &amp; 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) $&lt; -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>$&lt;</code>: Name of the first prerequisite.</li>
<li><code>$^</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 "&lt; = $&lt;"
	@echo "^ = $^"
	@echo "+ = $+"
	@echo "* = $*"
	@echo "----"

aaa:
bbb:
</code></pre>
<p>Running above <code>Makefile</code> gives:</p>
<pre><code class="language-text">@ = foobar
&lt; = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bar
----
@ = blabla
&lt; = 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)
# =&gt; 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))
# =&gt; 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))
# =&gt; 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, $(in))
# =&gt; out = a.a d.d
</code></pre>
<h3 id="abspath"><a class="header" href="#abspath"><code>abspath</code></a></h3>
<p>Resolve each file name as absolute path (don't resolve symlinks).</p>
<pre><code class="language-make">$(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 -&gt; $(call swap,first,second)"
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">call swap first second -&gt; 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) -&gt; $(2)"
endef

default: rule1 rule2

$(eval $(call new_rule,rule1,foo))
$(eval $(call new_rule,rule2,bar))
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">rule1 -&gt; foo
rule2 -&gt; bar
</code></pre>
<h3 id="foreach-ref"><a class="header" href="#foreach-ref">foreach (<a href="https://www.gnu.org/software/make/manual/html_node/Foreach-Function.html">ref</a>)</a></h3>
<p>Repeat a piece of text for a list of values, given the syntax <code>$(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) -&gt; $(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 -&gt; foo
rule2 -&gt; 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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                <ol class="chapter"><li class="chapter-item expanded affix "><a href="../intro.html">Introduction</a></li><li class="chapter-item expanded "><a href="../tools/index.html"><strong aria-hidden="true">1.</strong> Tools</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../tools/zsh.html"><strong aria-hidden="true">1.1.</strong> zsh</a></li><li class="chapter-item expanded "><a href="../tools/bash.html"><strong aria-hidden="true">1.2.</strong> bash</a></li><li class="chapter-item expanded "><a href="../tools/fish.html"><strong aria-hidden="true">1.3.</strong> fish</a></li><li class="chapter-item expanded "><a href="../tools/tmux.html"><strong aria-hidden="true">1.4.</strong> tmux</a></li><li class="chapter-item expanded "><a href="../tools/git.html"><strong aria-hidden="true">1.5.</strong> git</a></li><li class="chapter-item expanded "><a href="../tools/awk.html"><strong aria-hidden="true">1.6.</strong> awk</a></li><li class="chapter-item expanded 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html</a></li><li class="chapter-item expanded "><a href="../web/css.html"><strong aria-hidden="true">8.2.</strong> css</a></li><li class="chapter-item expanded "><a href="../web/chartjs.html"><strong aria-hidden="true">8.3.</strong> chartjs</a></li></ol></li><li class="chapter-item expanded "><a href="../arch/index.html"><strong aria-hidden="true">9.</strong> Arch</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../arch/x86_64.html"><strong aria-hidden="true">9.1.</strong> x86_64</a></li><li class="chapter-item expanded "><a href="../arch/arm64.html"><strong aria-hidden="true">9.2.</strong> arm64</a></li><li class="chapter-item expanded "><a href="../arch/armv7.html"><strong aria-hidden="true">9.3.</strong> armv7</a></li><li class="chapter-item expanded "><a href="../arch/riscv.html"><strong aria-hidden="true">9.4.</strong> riscv</a></li></ol></li></ol>
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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 &amp; 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) $&lt; -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>$&lt;</code>: Name of the first prerequisite.</li>
<li><code>$^</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 "&lt; = $&lt;"
	@echo "^ = $^"
	@echo "+ = $+"
	@echo "* = $*"
	@echo "----"

aaa:
bbb:
</code></pre>
<p>Running above <code>Makefile</code> gives:</p>
<pre><code class="language-text">@ = foobar
&lt; = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bar
----
@ = blabla
&lt; = 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)
# =&gt; 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))
# =&gt; 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))
# =&gt; 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, $(in))
# =&gt; out = a.a d.d
</code></pre>
<h3 id="abspath"><a class="header" href="#abspath"><code>abspath</code></a></h3>
<p>Resolve each file name as absolute path (don't resolve symlinks).</p>
<pre><code class="language-make">$(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 -&gt; $(call swap,first,second)"
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">call swap first second -&gt; 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) -&gt; $(2)"
endef

default: rule1 rule2

$(eval $(call new_rule,rule1,foo))
$(eval $(call new_rule,rule2,bar))
</code></pre>
<p>Outputs:</p>
<pre><code class="language-text">rule1 -&gt; foo
rule2 -&gt; bar
</code></pre>
<h3 id="foreach-ref"><a class="header" href="#foreach-ref">foreach (<a href="https://www.gnu.org/software/make/manual/html_node/Foreach-Function.html">ref</a>)</a></h3>
<p>Repeat a piece of text for a list of values, given the syntax <code>$(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) -&gt; $(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 -&gt; foo
rule2 -&gt; 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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