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Built-in Functions
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Numeric Functions
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<h1 id="builtin-functions">Built-in Functions</h1>
<p>카테고리가 많이 나누어져 있어서 함수가 많을것같지만 String, Numeric 함수를 제외하면 몇개 안됩니다.<br>그리고 String, Numeric 함수도 실제 많이 사용되는 함수들만 있습니다.</p>
<ul>
<li><a href="https://www.gnu.org/software/gawk/manual/html_node/Numeric-Functions.html" target="_blank"><b>Numeric Functions</b></a><br>
Functions that work with numbers, including <code>int()</code>, <code>sin()</code> and <code>rand()</code>.</li>
</ul>
<ul>
<li><a href="https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html" target="_blank"><b>String Functions</b></a><br>Functions for string manipulation, such as <code>split()</code>, <code>match()</code> and <code>sprintf()</code>.</li>
</ul>
<ul>
<li><a href="https://www.gnu.org/software/gawk/manual/html_node/I_002fO-Functions.html" target="_blank"><b>I/O Functions</b></a><br>Functions for files and shell commands.</li>
</ul>
<ul>
<li><a href="https://www.gnu.org/software/gawk/manual/html_node/Time-Functions.html" target="_blank"><b>Time Functions</b></a><br>Functions for dealing with timestamps.</li>
</ul>
<ul>
<li><a href="https://www.gnu.org/software/gawk/manual/html_node/Bitwise-Functions.html" target="_blank"><b>Bitwise Functions</b></a><br>Functions for bitwise operations.</li>
</ul>
<ul>
<li><a href="https://www.gnu.org/software/gawk/manual/html_node/Type-Functions.html" target="_blank"><b>Type Functions</b></a><br>Functions for type information.</li>
</ul>
<ul>
<li><a href="https://www.gnu.org/software/gawk/manual/html_node/I18N-Functions.html" target="_blank"><b>I18N Functions</b></a><br>Functions for string translation.</li>
</ul>
<h1 id="quiz">Quiz</h1>
<p>awk 는 주로 텍스트 데이터를 처리하는 용도로 사용되지만
<code>-b</code> 옵션을 이용하면 바이너리 데이터도 다룰 수 있습니다.</p>
<ol>
<li>다음은 /bin/date 실행파일 내에서 특정 4 바이트 값의 offset 을 구한 다음</li>
<li>+ 24 한 위치에서</li>
<li>4 바이트 값을 추출해서 hex 값을 출력하고</li>
<li>little endian 으로 처리한 정수값을 출력합니다.</li>
</ol>
<p>아래 붉은색으로 보이는 4 바이트 값이 offset 을 구할값이고 + 24
위치의 값이 흰색으로 처리된 부분입니다.</p>
<blockquote>
<p>"46 72 65 65" 값이 조회가 안될경우 hd -v /bin/date 출력에서 임의의 다른 값을 사용해도 됩니다.</p>
</blockquote>
<p><img src="images/function_ex.png" alt=""></p>
<p>awk 는 python 의 <code>chr()</code> 나 <code>ord()</code> 같은 함수가 없기 때문에
BEGIN 블록에서 먼저 256 개의 char 값을 index 로 하는 array 를 설정하여
<code>ord()</code> 함수에서처럼 쉽게 정수값을 구할 수 있게 합니다.</p>
<pre><code class="lang-bash">$ awk <span class="hljs-string">'BEGIN { printf "%c", 65 }'</span> <span class="hljs-comment"># chr(65) 와 같음</span>
A
$ awk <span class="hljs-string">'BEGIN {
for (i = 0; i <= 255; i++)
a[ sprintf("%c", i) ] = i
printf a["A"] # ord('</span>A<span class="hljs-string">') 와 같음
}'</span>
<span class="hljs-number">65</span>
</code></pre>
<p>RS 값을 <code>"^$"</code> 로 설정하였으므로 전체 데이터가 하나의 레코드로 입력이 되겠고
FS 값이 <code>""</code> 이므로 각각의 바이트 값이 하나의 필드값과 매칭이 됩니다.
따라서 NF 값은 파일 사이즈와 같게 되겠죠.</p>
<pre><code class="lang-bash">$ awk -b <span class="hljs-operator">-f</span> - <<\EOF val=<span class="hljs-number">0</span>x46726565 /bin/date
BEGIN {
RS=<span class="hljs-string">"^$"</span>; FS=<span class="hljs-string">""</span>
<span class="hljs-keyword">for</span> (i = <span class="hljs-number">0</span>; i <= <span class="hljs-number">255</span>; i++) a[ sprintf(<span class="hljs-string">"%c"</span>, i) ] = i
}{
<span class="hljs-built_in">print</span> <span class="hljs-string">"file size : "</span> length(<span class="hljs-variable">$0</span>)
<span class="hljs-comment"># 외부로부터 입력되는 val=0x46726565 값은 스트링이므로 index 함수로</span>
<span class="hljs-comment"># 바이너리 파일 내에서 바이트 값을 검색하려면 먼저 char 값으로 변경합니다.</span>
patsplit(val, f, /.{<span class="hljs-number">2</span>}/)
v = sprintf(<span class="hljs-string">"%c%c%c%c"</span>, strtonum(<span class="hljs-string">"0x"</span> f[<span class="hljs-number">2</span>]), strtonum(<span class="hljs-string">"0x"</span> f[<span class="hljs-number">3</span>]), \
strtonum(<span class="hljs-string">"0x"</span> f[<span class="hljs-number">4</span>]), strtonum(<span class="hljs-string">"0x"</span> f[<span class="hljs-number">5</span>]))
<span class="hljs-keyword">if</span> ( (i2 = index(<span class="hljs-variable">$0</span>, v)) > <span class="hljs-number">0</span> )
<span class="hljs-built_in">print</span> <span class="hljs-string">"value "</span> val <span class="hljs-string">" found! at : "</span> i2 <span class="hljs-string">" offset"</span>
<span class="hljs-keyword">else</span>
<span class="hljs-built_in">exit</span> <span class="hljs-number">1</span>
<span class="hljs-comment"># offset + 24 한 위치에서 4 바이트의 hex 값을 출력합니다.</span>
i = i2 + <span class="hljs-number">24</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"4 bytes hex value at "</span> i2 <span class="hljs-string">" + 24 : "</span>)
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"0x%02x%02x%02x%02x\n"</span>, a[$(i)], a[$(i+<span class="hljs-number">1</span>)], a[$(i+<span class="hljs-number">2</span>)], a[$(i+<span class="hljs-number">3</span>)])
<span class="hljs-comment"># little endian 으로 정수값을 출력해야 하므로 a[$i] 값이 끝으로 갑니다.</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"convert to decimal value : "</span>)
le = sprintf(<span class="hljs-string">"0x%02x%02x%02x%02x"</span>, a[$(i+<span class="hljs-number">3</span>)], a[$(i+<span class="hljs-number">2</span>)], a[$(i+<span class="hljs-number">1</span>)], a[$(i)])
<span class="hljs-built_in">print</span> strtonum(le) <span class="hljs-string">" (little endian)"</span>
}
EOF
file size : <span class="hljs-number">104960</span>
value <span class="hljs-number">0</span>x46726565 found! at : <span class="hljs-number">93521</span> offset
<span class="hljs-number">4</span> bytes hex value at <span class="hljs-number">93521</span> + <span class="hljs-number">24</span> : <span class="hljs-number">0</span>x2c20496e
convert to decimal value : <span class="hljs-number">1850286124</span> (little endian)
</code></pre>
<p>offset 을 구할 때 사용되는 hex 값이 외부로부터 스트링으로 입력되는 경우에는 검색을 위해
스트링 -> char 변환을 거쳐야 되므로 다음은 직접 스크립트 내에서 설정해 사용합니다.
그리고 정수값을 출력할 때 53 bits 를 초과하는 값이면 <code>-M</code> 옵션을 사용해야
올바르게 값이 출력됩니다.</p>
<pre><code class="lang-bash">$ awk -b <span class="hljs-operator">-f</span> - <<\EOF /bin/date
BEGIN {
RS=<span class="hljs-string">"^$"</span>; FS=<span class="hljs-string">""</span>
<span class="hljs-keyword">for</span> (i = <span class="hljs-number">0</span>; i <= <span class="hljs-number">255</span>; i++) a[ sprintf(<span class="hljs-string">"%c"</span>, i) ] = i
}{
<span class="hljs-built_in">print</span> <span class="hljs-string">"file size : "</span> length(<span class="hljs-variable">$0</span>)
v = <span class="hljs-string">"\x46\x72\x65\x65"</span> <span class="hljs-comment"># 직접 스크립트 내에서 검색할 바이트 값을 설정</span>
patsplit(v, f, /./)
val = sprintf( <span class="hljs-string">"0x%02x%02x%02x%02x"</span>, a[f[<span class="hljs-number">1</span>]], a[f[<span class="hljs-number">2</span>]], a[f[<span class="hljs-number">3</span>]], a[f[<span class="hljs-number">4</span>]] )
<span class="hljs-keyword">if</span> ( (i2 = index(<span class="hljs-variable">$0</span>, v)) > <span class="hljs-number">0</span> )
<span class="hljs-built_in">print</span> <span class="hljs-string">"value "</span> val <span class="hljs-string">" found! at : "</span> i2 <span class="hljs-string">" offset"</span>
<span class="hljs-keyword">else</span>
<span class="hljs-built_in">exit</span> <span class="hljs-number">1</span>
i = i2 + <span class="hljs-number">24</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"4 bytes hex value at "</span> i2 <span class="hljs-string">" + 24 : "</span>)
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"0x%02x%02x%02x%02x\n"</span>, a[$(i)], a[$(i+<span class="hljs-number">1</span>)], a[$(i+<span class="hljs-number">2</span>)], a[$(i+<span class="hljs-number">3</span>)])
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"convert to decimal value : "</span>)
le = sprintf(<span class="hljs-string">"0x%02x%02x%02x%02x"</span>, a[$(i+<span class="hljs-number">3</span>)], a[$(i+<span class="hljs-number">2</span>)], a[$(i+<span class="hljs-number">1</span>)], a[$(i)])
<span class="hljs-comment"># 출력하는 정수값이 53 bits 를 초과하면 '-M' 옵션을 사용해야 합니다.</span>
<span class="hljs-built_in">print</span> strtonum(le) <span class="hljs-string">" (little endian)"</span>
}
EOF
</code></pre>
<h1 id="2-">2 .</h1>
<p><code>/proc/net/tcp</code> 값을 출력해보면 <code>local_address</code> 와 <code>rem_address</code> 값이 16 진수로 나오는데요.
이것을 10 진수로 바꾸어서 출력하는 것입니다.
이때 한가지 주의할 점은 바이트 값의 순서입니다.</p>
<p><img src="images/proc_net_tcp.png" alt=""></p>
<pre><code class="lang-bash">$ less /proc/net/tcp
sl <span class="hljs-built_in">local</span>_address rem_address st tx_queue rx_queue tr tm->when ....
<span class="hljs-number">0</span>: <span class="hljs-number">017</span>AA8C0:<span class="hljs-number">0035</span> <span class="hljs-number">00000000</span>:<span class="hljs-number">0000</span> <span class="hljs-number">0</span>A <span class="hljs-number">00000000</span>:<span class="hljs-number">00000000</span> <span class="hljs-number">00</span>:<span class="hljs-number">00000000</span> ....
<span class="hljs-number">1</span>: <span class="hljs-number">3500007</span>F:<span class="hljs-number">0035</span> <span class="hljs-number">00000000</span>:<span class="hljs-number">0000</span> <span class="hljs-number">0</span>A <span class="hljs-number">00000000</span>:<span class="hljs-number">00000000</span> <span class="hljs-number">00</span>:<span class="hljs-number">00000000</span> ....
<span class="hljs-number">2</span>: <span class="hljs-number">0100007</span>F:<span class="hljs-number">0277</span> <span class="hljs-number">00000000</span>:<span class="hljs-number">0000</span> <span class="hljs-number">0</span>A <span class="hljs-number">00000000</span>:<span class="hljs-number">00000000</span> <span class="hljs-number">00</span>:<span class="hljs-number">00000000</span> ....
<span class="hljs-number">3</span>: <span class="hljs-number">0100007</span>F:<span class="hljs-number">823</span>D <span class="hljs-number">00000000</span>:<span class="hljs-number">0000</span> <span class="hljs-number">0</span>A <span class="hljs-number">00000000</span>:<span class="hljs-number">00000000</span> <span class="hljs-number">00</span>:<span class="hljs-number">00000000</span> ....
<span class="hljs-number">4</span>: <span class="hljs-number">66</span>D0C0D3:<span class="hljs-number">9726</span> <span class="hljs-number">901</span>F123B:<span class="hljs-number">01</span>BB <span class="hljs-number">01</span> <span class="hljs-number">00000000</span>:<span class="hljs-number">00000000</span> <span class="hljs-number">02</span>:<span class="hljs-number">00000693</span> ....
<span class="hljs-number">5</span>: <span class="hljs-number">66</span>D0C0D3:ECEA <span class="hljs-number">9923</span>E69D:<span class="hljs-number">01</span>BB <span class="hljs-number">01</span> <span class="hljs-number">00000000</span>:<span class="hljs-number">00000000</span> <span class="hljs-number">02</span>:<span class="hljs-number">00000734</span> ....
<span class="hljs-number">6</span>: <span class="hljs-number">66</span>D0C0D3:E366 E5C53AD8:<span class="hljs-number">01</span>BB <span class="hljs-number">06</span> <span class="hljs-number">00000000</span>:<span class="hljs-number">00000000</span> <span class="hljs-number">03</span>:<span class="hljs-number">00000110</span> ....
. . . .
. . . .
$ awk <span class="hljs-operator">-f</span> - <<\EOF /proc/net/tcp
NR > <span class="hljs-number">1</span> {
loc_ip = getip( substr(<span class="hljs-variable">$2</span>,<span class="hljs-number">1</span>,<span class="hljs-number">8</span>))
loc_port = strtonum(<span class="hljs-string">"0x"</span> substr(<span class="hljs-variable">$2</span>,<span class="hljs-number">10</span>,<span class="hljs-number">4</span>))
rem_ip = getip( substr(<span class="hljs-variable">$3</span>,<span class="hljs-number">1</span>,<span class="hljs-number">8</span>))
rem_port = strtonum(<span class="hljs-string">"0x"</span> substr(<span class="hljs-variable">$3</span>,<span class="hljs-number">10</span>,<span class="hljs-number">4</span>))
<span class="hljs-built_in">printf</span> <span class="hljs-string">"%-30s %s\n"</span>, loc_ip <span class="hljs-string">":"</span> loc_port, rem_ip <span class="hljs-string">":"</span> rem_port
}
<span class="hljs-keyword">function</span> getip( str, i, n, f, res) {
n = patsplit( str, f, /[[:xdigit:]]{<span class="hljs-number">2</span>}/)
<span class="hljs-keyword">for</span> ( i = n; i >= <span class="hljs-number">1</span>; i-- )
res = res sprintf(<span class="hljs-string">"%s%s"</span>, strtonum(<span class="hljs-string">"0x"</span> f[i]), (i > <span class="hljs-number">1</span>) ? <span class="hljs-string">"."</span> : <span class="hljs-string">""</span>)
<span class="hljs-built_in">return</span> res
}
EOF
<span class="hljs-number">192.168</span>.<span class="hljs-number">122.1</span>:<span class="hljs-number">53</span> <span class="hljs-number">0.0</span>.<span class="hljs-number">0.0</span>:<span class="hljs-number">0</span>
<span class="hljs-number">127.0</span>.<span class="hljs-number">0.53</span>:<span class="hljs-number">53</span> <span class="hljs-number">0.0</span>.<span class="hljs-number">0.0</span>:<span class="hljs-number">0</span>
<span class="hljs-number">127.0</span>.<span class="hljs-number">0.1</span>:<span class="hljs-number">631</span> <span class="hljs-number">0.0</span>.<span class="hljs-number">0.0</span>:<span class="hljs-number">0</span>
<span class="hljs-number">127.0</span>.<span class="hljs-number">0.1</span>:<span class="hljs-number">33341</span> <span class="hljs-number">0.0</span>.<span class="hljs-number">0.0</span>:<span class="hljs-number">0</span>
<span class="hljs-number">211.192</span>.<span class="hljs-number">208.102</span>:<span class="hljs-number">38694</span> <span class="hljs-number">59.18</span>.<span class="hljs-number">31.144</span>:<span class="hljs-number">443</span>
<span class="hljs-number">211.192</span>.<span class="hljs-number">208.102</span>:<span class="hljs-number">60650</span> <span class="hljs-number">157.230</span>.<span class="hljs-number">35.153</span>:<span class="hljs-number">443</span>
<span class="hljs-number">211.192</span>.<span class="hljs-number">208.102</span>:<span class="hljs-number">58214</span> <span class="hljs-number">216.58</span>.<span class="hljs-number">197.229</span>:<span class="hljs-number">443</span>
<span class="hljs-number">211.192</span>.<span class="hljs-number">208.102</span>:<span class="hljs-number">36740</span> <span class="hljs-number">52.42</span>.<span class="hljs-number">195.146</span>:<span class="hljs-number">443</span>
. . . .
. . . .
</code></pre>
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