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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="../shells/index.html"><strong aria-hidden="true">1.</strong> Shells</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../shells/zsh.html"><strong aria-hidden="true">1.1.</strong> zsh</a></li><li class="chapter-item expanded "><a href="../shells/bash.html"><strong aria-hidden="true">1.2.</strong> bash</a></li><li class="chapter-item expanded "><a href="../shells/fish.html"><strong aria-hidden="true">1.3.</strong> fish</a></li></ol></li><li class="chapter-item expanded "><a href="../cli/index.html"><strong aria-hidden="true">2.</strong> CLI foo</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../cli/awk.html" class="active"><strong aria-hidden="true">2.1.</strong> awk</a></li><li class="chapter-item expanded "><a href="../cli/sed.html"><strong aria-hidden="true">2.2.</strong> sed</a></li><li class="chapter-item expanded "><a href="../cli/column.html"><strong aria-hidden="true">2.3.</strong> column</a></li><li class="chapter-item expanded "><a href="../cli/sort.html"><strong aria-hidden="true">2.4.</strong> sort</a></li><li class="chapter-item expanded "><a href="../cli/tr.html"><strong aria-hidden="true">2.5.</strong> tr</a></li><li class="chapter-item expanded "><a href="../cli/tac.html"><strong aria-hidden="true">2.6.</strong> tac</a></li><li class="chapter-item expanded "><a href="../cli/paste.html"><strong aria-hidden="true">2.7.</strong> paste</a></li></ol></li><li class="chapter-item expanded "><a href="../tools/index.html"><strong aria-hidden="true">3.</strong> Tools</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../tools/tmux.html"><strong aria-hidden="true">3.1.</strong> tmux</a></li><li class="chapter-item expanded "><a href="../tools/emacs.html"><strong aria-hidden="true">3.2.</strong> emacs</a></li><li class="chapter-item expanded "><a href="../tools/gpg.html"><strong aria-hidden="true">3.3.</strong> gpg</a></li><li class="chapter-item expanded "><a href="../tools/radare2.html"><strong aria-hidden="true">3.4.</strong> radare2</a></li><li class="chapter-item expanded "><a href="../tools/qemu.html"><strong aria-hidden="true">3.5.</strong> qemu</a></li><li class="chapter-item expanded "><a href="../tools/pacman.html"><strong aria-hidden="true">3.6.</strong> pacman</a></li><li class="chapter-item expanded "><a href="../tools/dot.html"><strong aria-hidden="true">3.7.</strong> dot</a></li><li class="chapter-item expanded "><a href="../tools/ffmpeg.html"><strong aria-hidden="true">3.8.</strong> ffmpeg</a></li><li class="chapter-item expanded "><a href="../tools/gnuplot.html"><strong aria-hidden="true">3.9.</strong> gnuplot</a></li><li class="chapter-item expanded "><a href="../tools/restic.html"><strong aria-hidden="true">3.10.</strong> restic</a></li><li class="chapter-item expanded "><a href="../tools/qrencode.html"><strong aria-hidden="true">3.11.</strong> qrencode</a></li></ol></li><li class="chapter-item expanded "><a href="../process/index.html"><strong aria-hidden="true">4.</strong> Process management & inspection</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../process/lsof.html"><strong aria-hidden="true">4.1.</strong> lsof</a></li><li class="chapter-item expanded "><a href="../process/pidstat.html"><strong aria-hidden="true">4.2.</strong> pidstat</a></li><li class="chapter-item expanded "><a href="../process/pgrep.html"><strong aria-hidden="true">4.3.</strong> pgrep</a></li><li class="chapter-item expanded "><a href="../process/ps.html"><strong aria-hidden="true">4.4.</strong> ps</a></li><li class="chapter-item expanded "><a href="../process/pmap.html"><strong aria-hidden="true">4.5.</strong> pmap</a></li><li class="chapter-item expanded "><a href="../process/pstack.html"><strong aria-hidden="true">4.6.</strong> pstack</a></li><li class="chapter-item expanded "><a href="../process/taskset.html"><strong aria-hidden="true">4.7.</strong> taskset</a></li><li class="chapter-item expanded "><a href="../process/nice.html"><strong aria-hidden="true">4.8.</strong> nice</a></li></ol></li><li class="chapter-item expanded "><a href="../trace_profile/index.html"><strong aria-hidden="true">5.</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">5.1.</strong> time</a></li><li class="chapter-item expanded "><a href="../trace_profile/strace.html"><strong aria-hidden="true">5.2.</strong> strace</a></li><li class="chapter-item expanded "><a href="../trace_profile/ltrace.html"><strong aria-hidden="true">5.3.</strong> ltrace</a></li><li class="chapter-item expanded "><a href="../trace_profile/perf.html"><strong aria-hidden="true">5.4.</strong> perf</a></li><li class="chapter-item expanded "><a href="../trace_profile/oprofile.html"><strong aria-hidden="true">5.5.</strong> OProfile</a></li><li class="chapter-item expanded "><a href="../trace_profile/callgrind.html"><strong aria-hidden="true">5.6.</strong> callgrind</a></li></ol></li><li class="chapter-item expanded "><a href="../debug/index.html"><strong aria-hidden="true">6.</strong> Debug</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../debug/gdb.html"><strong aria-hidden="true">6.1.</strong> gdb</a></li><li class="chapter-item expanded "><a href="../debug/gdbserver.html"><strong aria-hidden="true">6.2.</strong> gdbserver</a></li></ol></li><li class="chapter-item expanded "><a href="../binary/index.html"><strong aria-hidden="true">7.</strong> Binary</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binary/od.html"><strong aria-hidden="true">7.1.</strong> od</a></li><li class="chapter-item expanded "><a href="../binary/xxd.html"><strong aria-hidden="true">7.2.</strong> xxd</a></li><li class="chapter-item expanded "><a href="../binary/readelf.html"><strong aria-hidden="true">7.3.</strong> readelf</a></li><li class="chapter-item expanded "><a href="../binary/objdump.html"><strong aria-hidden="true">7.4.</strong> objdump</a></li><li class="chapter-item expanded "><a href="../binary/nm.html"><strong aria-hidden="true">7.5.</strong> nm</a></li></ol></li><li class="chapter-item expanded "><a href="../development/index.html"><strong aria-hidden="true">8.</strong> Development</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/c++filt.html"><strong aria-hidden="true">8.1.</strong> c++filt</a></li><li class="chapter-item expanded "><a href="../development/c++.html"><strong aria-hidden="true">8.2.</strong> c++</a></li><li class="chapter-item expanded "><a href="../development/glibc.html"><strong aria-hidden="true">8.3.</strong> glibc</a></li><li class="chapter-item expanded "><a href="../development/gcc.html"><strong aria-hidden="true">8.4.</strong> gcc</a></li><li class="chapter-item expanded "><a href="../development/git.html"><strong aria-hidden="true">8.5.</strong> git</a></li><li class="chapter-item expanded "><a href="../development/cmake.html"><strong aria-hidden="true">8.6.</strong> cmake</a></li><li class="chapter-item expanded "><a href="../development/make.html"><strong aria-hidden="true">8.7.</strong> make</a></li><li class="chapter-item expanded "><a href="../development/ld.so.html"><strong aria-hidden="true">8.8.</strong> ld.so</a></li><li class="chapter-item expanded "><a href="../development/symbolver.html"><strong aria-hidden="true">8.9.</strong> symbol versioning</a></li><li class="chapter-item expanded "><a href="../development/python.html"><strong aria-hidden="true">8.10.</strong> python</a></li><li class="chapter-item expanded "><a href="../development/gcov.html"><strong aria-hidden="true">8.11.</strong> gcov</a></li><li class="chapter-item expanded "><a href="../development/pgo.html"><strong aria-hidden="true">8.12.</strong> pgo</a></li></ol></li><li class="chapter-item expanded "><a href="../linux/index.html"><strong aria-hidden="true">9.</strong> Linux</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../linux/systemd.html"><strong aria-hidden="true">9.1.</strong> systemd</a></li><li class="chapter-item expanded "><a href="../linux/coredump.html"><strong aria-hidden="true">9.2.</strong> coredump</a></li><li class="chapter-item expanded "><a href="../linux/ptrace_scope.html"><strong aria-hidden="true">9.3.</strong> ptrace_scope</a></li><li class="chapter-item expanded "><a href="../linux/cryptsetup.html"><strong aria-hidden="true">9.4.</strong> cryptsetup</a></li><li class="chapter-item expanded "><a href="../linux/swap.html"><strong aria-hidden="true">9.5.</strong> swap</a></li><li class="chapter-item expanded "><a href="../linux/input.html"><strong aria-hidden="true">9.6.</strong> input</a></li><li class="chapter-item expanded "><a href="../linux/acl.html"><strong aria-hidden="true">9.7.</strong> acl</a></li><li class="chapter-item expanded "><a href="../linux/zfs.html"><strong aria-hidden="true">9.8.</strong> zfs</a></li><li class="chapter-item expanded "><a href="../linux/cpufreq.html"><strong aria-hidden="true">9.9.</strong> cpufreq</a></li><li class="chapter-item expanded "><a href="../linux/cups.html"><strong aria-hidden="true">9.10.</strong> cups</a></li></ol></li><li class="chapter-item expanded "><a href="../network/index.html"><strong aria-hidden="true">10.</strong> Network</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../network/ssh.html"><strong aria-hidden="true">10.1.</strong> ssh</a></li><li class="chapter-item expanded "><a href="../network/ss.html"><strong aria-hidden="true">10.2.</strong> ss</a></li><li class="chapter-item expanded "><a href="../network/tcpdump.html"><strong aria-hidden="true">10.3.</strong> tcpdump</a></li><li class="chapter-item expanded "><a href="../network/tshark.html"><strong aria-hidden="true">10.4.</strong> tshark</a></li><li class="chapter-item expanded "><a href="../network/firewall-cmd.html"><strong aria-hidden="true">10.5.</strong> firewall-cmd</a></li><li class="chapter-item expanded "><a href="../network/nftables.html"><strong aria-hidden="true">10.6.</strong> nftables</a></li></ol></li><li class="chapter-item expanded "><a href="../web/index.html"><strong aria-hidden="true">11.</strong> Web</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../web/html.html"><strong aria-hidden="true">11.1.</strong> html</a></li><li class="chapter-item expanded "><a href="../web/css.html"><strong aria-hidden="true">11.2.</strong> css</a></li><li class="chapter-item expanded "><a href="../web/chartjs.html"><strong aria-hidden="true">11.3.</strong> chartjs</a></li></ol></li><li class="chapter-item expanded "><a href="../arch/index.html"><strong aria-hidden="true">12.</strong> Arch</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../arch/x86_64.html"><strong aria-hidden="true">12.1.</strong> x86_64</a></li><li class="chapter-item expanded "><a href="../arch/armv8.html"><strong aria-hidden="true">12.2.</strong> armv8</a></li><li class="chapter-item expanded "><a href="../arch/arm64.html"><strong aria-hidden="true">12.3.</strong> arm64</a></li><li class="chapter-item expanded "><a href="../arch/armv7.html"><strong aria-hidden="true">12.4.</strong> armv7</a></li><li class="chapter-item expanded "><a href="../arch/riscv.html"><strong aria-hidden="true">12.5.</strong> riscv</a></li></ol></li></ol>
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<h1 id="awk1"><a class="header" href="#awk1">awk(1)</a></h1>
<pre><code class="language-markdown">awk [opt] program [input]
-F <sepstr> field separator string (can be regex)
program awk program
input file or stdin if not file given
</code></pre>
<h2 id="input-processing"><a class="header" href="#input-processing">Input processing</a></h2>
<p>Input is processed in two stages:</p>
<ol>
<li>Splitting input into a sequence of <code>records</code>.
By default split at <code>newline</code> character, but can be changed via the
builtin <code>RS</code> variable.</li>
<li>Splitting a <code>record</code> into <code>fields</code>. By default strings without <code>whitespace</code>,
but can be changed via the builtin variable <code>FS</code> or command line option
<code>-F</code>.</li>
</ol>
<p>Fields are accessed as follows:</p>
<ul>
<li><code>$0</code> whole <code>record</code></li>
<li><code>$1</code> field one</li>
<li><code>$2</code> field two</li>
<li>...</li>
</ul>
<h2 id="program"><a class="header" href="#program">Program</a></h2>
<p>An <code>awk</code> program is composed of pairs of the form:</p>
<pre><code class="language-markdown">pattern { action }
</code></pre>
<p>The program is run against each <code>record</code> in the input stream. If a <code>pattern</code>
matches a <code>record</code> the corresponding <code>action</code> is executed and can access the
<code>fields</code>.</p>
<pre><code class="language-markdown">INPUT
|
v
record ----> ∀ pattern matched
| |
v v
fields ----> run associated action
</code></pre>
<p>Any valid awk <code>expr</code> can be a <code>pattern</code>.</p>
<p>An example is the regex pattern <code>/abc/ { print $1 }</code> which prints the first
field if the record matches the regex <code>/abc/</code>. This form is actually a short
version for <code>$0 ~ /abc/ { print $1 }</code>, see the regex comparison operator
below.</p>
<h3 id="special-pattern"><a class="header" href="#special-pattern">Special pattern</a></h3>
<p>awk provides two special patterns, <code>BEGIN</code> and <code>END</code>, which can be used
multiple times. Actions with those patterns are <strong>executed exactly once</strong>.</p>
<ul>
<li><code>BEGIN</code> actions are run before processing the first record</li>
<li><code>END</code> actions are run after processing the last record</li>
</ul>
<h3 id="special-variables"><a class="header" href="#special-variables">Special variables</a></h3>
<ul>
<li><code>RS</code> <em>record separator</em>: first char is the record separator, by default
<newline></li>
<li><code>FS</code> <em>field separator</em>: regex to split records into fields, by default
<space></li>
<li><code>NR</code> <em>number record</em>: number of current record</li>
<li><code>NF</code> <em>number fields</em>: number of fields in the current record</li>
</ul>
<h3 id="special-statements--functions"><a class="header" href="#special-statements--functions">Special statements & functions</a></h3>
<ul>
<li>
<p><code>printf "fmt", args...</code></p>
<p>Print format string, args are comma separated.</p>
<ul>
<li><code>%s</code> string</li>
<li><code>%d</code> decimal</li>
<li><code>%x</code> hex</li>
<li><code>%f</code> float</li>
</ul>
<p>Width can be specified as <code>%Ns</code>, this reserves <code>N</code> chars for a string.
For floats one can use <code>%N.Mf</code>, <code>N</code> is the total number including <code>.</code> and
<code>M</code>.</p>
</li>
<li>
<p><code>sprintf("fmt", expr, ...)</code></p>
<p>Format the expressions according to the format string. Similar as <code>printf</code>,
but this is a function and return value can be assigned to a variable.</p>
</li>
<li>
<p><code>strftime("fmt")</code></p>
<p>Print time stamp formatted by <code>fmt</code>.</p>
<ul>
<li><code>%Y</code> full year (eg 2020)</li>
<li><code>%m</code> month (01-12)</li>
<li><code>%d</code> day (01-31)</li>
<li><code>%F</code> alias for <code>%Y-%m-%d</code></li>
<li><code>%H</code> hour (00-23)</li>
<li><code>%M</code> minute (00-59)</li>
<li><code>%S</code> second (00-59)</li>
<li><code>%T</code> alias for <code>%H:%M:%S</code></li>
</ul>
</li>
<li>
<p><code>S ~ R</code>, <code>S !~ R</code></p>
<p>The regex comparison operator, where the former returns true if the string
<code>S</code> matches the regex <code>R</code>, and the latter is the negated form.
The regex can be either a
<a href="https://www.gnu.org/software/gawk/manual/html_node/Regexp-Usage.html">constant</a>
or <a href="https://www.gnu.org/software/gawk/manual/html_node/Computed-Regexps.html">dynamic</a>
regex.</p>
</li>
</ul>
<h2 id="examples"><a class="header" href="#examples">Examples</a></h2>
<h3 id="filter-records"><a class="header" href="#filter-records">Filter records</a></h3>
<pre><code class="language-bash">awk 'NR%2 == 0 { print $0 }' <file>
</code></pre>
<p>The pattern <code>NR%2 == 0</code> matches every second record and the action <code>{ print $0 }</code>
prints the whole record.</p>
<h3 id="negative-patterns"><a class="header" href="#negative-patterns">Negative patterns</a></h3>
<pre><code class="language-bash">awk '!/^#/ { print $1 }' <file>
</code></pre>
<p>Matches records not starting with <code>#</code>.</p>
<h3 id="range-patterns"><a class="header" href="#range-patterns">Range patterns</a></h3>
<pre><code class="language-bash">echo -e "a\nFOO\nb\nc\nBAR\nd" | \
awk '/FOO/,/BAR/ { print }'
</code></pre>
<p><code>/FOO/,/BAR/</code> define a range pattern of <code>begin_pattern, end_pattern</code>. When
<code>begin_pattern</code> is matched the range is <strong>turned on</strong> and when the
<code>end_pattern</code> is matched the range is <strong>turned off</strong>. This matches every record
in the range <em>inclusive</em>.</p>
<p>An <em>exclusive</em> range must be handled explicitly, for example as follows.</p>
<pre><code class="language-bash">echo -e "a\nFOO\nb\nc\nBAR\nd" | \
awk '/FOO/,/BAR/ { if (!($1 ~ "FOO") && !($1 ~ "BAR")) { print } }'
</code></pre>
<h3 id="access-last-fields-in-records"><a class="header" href="#access-last-fields-in-records">Access last fields in records</a></h3>
<pre><code class="language-bash">echo 'a b c d e f' | awk '{ print $NF $(NF-1) }'
</code></pre>
<p>Access last fields with arithmetic on the <code>NF</code> number of fields variable.</p>
<h3 id="split-on-multiple-tokens"><a class="header" href="#split-on-multiple-tokens">Split on multiple tokens</a></h3>
<pre><code class="language-bash">echo 'a,b;c:d' | awk -F'[,;:]' '{ printf "1=%s | 4=%s\n", $1, $4 }'
</code></pre>
<p>Use regex as field separator.</p>
<h3 id="capture-in-variables"><a class="header" href="#capture-in-variables">Capture in variables</a></h3>
<pre><code class="language-bash"># /proc/<pid>/status
# Name: cat
# ...
# VmRSS: 516 kB
# ...
for f in /proc/*/status; do
cat $f | awk '
/^VmRSS/ { rss = $2/1024 }
/^Name/ { name = $2 }
END { printf "%16s %6d MB\n", name, rss }';
done | sort -k2 -n
</code></pre>
<p>We capture values from <code>VmRSS</code> and <code>Name</code> into variables and print them at the
<code>END</code> once processing all records is done.</p>
<h3 id="capture-in-array"><a class="header" href="#capture-in-array">Capture in array</a></h3>
<pre><code class="language-bash">echo 'a 10
b 2
b 4
a 1' | awk '{
vals[$1] += $2
cnts[$1] += 1
}
END {
for (v in vals)
printf "%s %d\n", v, vals[v] / cnts [v]
}'
</code></pre>
<p>Capture keys and values from different columns and some up the values.
At the <code>END</code> we compute the average of each key.</p>
<h3 id="run-shell-command-and-capture-output"><a class="header" href="#run-shell-command-and-capture-output">Run shell command and capture output</a></h3>
<pre><code class="language-bash">cat /proc/1/status | awk '
/^Pid/ {
"ps --no-header -o user " $2 | getline user;
print user
}'
</code></pre>
<p>We build a <code>ps</code> command line and capture the first line of the processes output
in the <code>user</code> variable and then print it.</p>
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