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<!DOCTYPE HTML>
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<b>6.</b>
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<b>8.</b>
getline
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<b>9.</b>
Arrays
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<b>9.1.</b>
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<b>9.3.</b>
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<b>9.4.</b>
Subquery
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<b>9.5.</b>
Index
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<b>10.</b>
Control Statements
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<b>11.</b>
Operators
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<b>12.</b>
Built-in Functions
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<b>12.1.</b>
Numeric Functions
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<b>12.2.</b>
String Functions
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<b>12.3.</b>
I/O Functions
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<b>12.4.</b>
Time Functions
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<b>12.5.</b>
Bitwise Functions
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<b>12.6.</b>
Type Functions
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Dynamic Extensions
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TCP/IP Internetworking
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<b>17.</b>
Tips
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<h1 id="tips">Tips</h1>
<h4 id="shell-변수값-설정-방법">shell 변수값 설정 방법</h4>
<p>awk 는 child process 로 실행되므로 실행 중에 현재 shell 의 변수값을 설정할 수 없습니다.
하지만 shell eval 명령을 활용하면 shell 변수값을 설정할 수 있습니다.</p>
<pre><code class="lang-bash"><span class="hljs-keyword">for</span> tuple <span class="hljs-keyword">in</span> \
INTEL_FAM6_KABYLAKE_DESKTOP,<span class="hljs-number">0</span>x0B,<span class="hljs-number">0</span>x80 \
INTEL_FAM6_SKYLAKE_X,<span class="hljs-number">0</span>x03,<span class="hljs-number">0</span>x0100013e \
INTEL_FAM6_BROADWELL_CORE,<span class="hljs-number">0</span>x04,<span class="hljs-number">0</span>x28 \
INTEL_FAM6_HASWELL_ULT,<span class="hljs-number">0</span>x01,<span class="hljs-number">0</span>x21 \
INTEL_FAM6_IVYBRIDGE_X,<span class="hljs-number">0</span>x04,<span class="hljs-number">0</span>x42a \
INTEL_FAM6_SANDYBRIDGE_X,<span class="hljs-number">0</span>x07,<span class="hljs-number">0</span>x712
<span class="hljs-keyword">do</span> <span class="hljs-comment"># 명령치환을 이용한 model, stepping, ucode 변수값 설정</span>
model=$(<span class="hljs-built_in">echo</span> <span class="hljs-variable">$tuple</span> | cut <span class="hljs-operator">-d</span>, <span class="hljs-operator">-f</span>1)
stepping=$(( $(<span class="hljs-built_in">echo</span> <span class="hljs-variable">$tuple</span> | cut <span class="hljs-operator">-d</span>, <span class="hljs-operator">-f</span>2) ))
ucode=$(<span class="hljs-built_in">echo</span> <span class="hljs-variable">$tuple</span> | cut <span class="hljs-operator">-d</span>, <span class="hljs-operator">-f</span>3)
<span class="hljs-keyword">if</span> [ <span class="hljs-string">"<span class="hljs-variable">$cpu_model</span>"</span> = <span class="hljs-string">"<span class="hljs-variable">$model</span>"</span> ] && [ <span class="hljs-string">"<span class="hljs-variable">$cpu_stepping</span>"</span> = <span class="hljs-string">"<span class="hljs-variable">$stepping</span>"</span> ]
<span class="hljs-keyword">then</span>
. . . .
. . . .
<span class="hljs-keyword">done</span>
-------------------------------------------------------------------------
<span class="hljs-keyword">for</span> tuple <span class="hljs-keyword">in</span> \
. . .
<span class="hljs-keyword">do</span> <span class="hljs-comment"># eval 과 awk 를 활용하여 간단히 작성</span>
<span class="hljs-built_in">eval</span> <span class="hljs-string">"<span class="hljs-variable">$( echo "$tuple" |
awk -F, '{ printf "model=%s; stepping=%s; ucode=%s;",$1,strtonum($2)</span>,<span class="hljs-variable">$3</span> }' )"</span>
<span class="hljs-keyword">if</span> [ <span class="hljs-string">"<span class="hljs-variable">$cpu_model</span>"</span> = <span class="hljs-string">"<span class="hljs-variable">$model</span>"</span> ] && [ <span class="hljs-string">"<span class="hljs-variable">$cpu_stepping</span>"</span> = <span class="hljs-string">"<span class="hljs-variable">$stepping</span>"</span> ]
<span class="hljs-keyword">then</span>
. . . .
. . . .
<span class="hljs-keyword">done</span>
</code></pre>
<p>shell 의 declare, local, export, eval 를 이용하여도 변수값을 설정할 수 있습니다.</p>
<pre><code class="lang-bash">$ <span class="hljs-function"><span class="hljs-title">f1</span></span>() {
<span class="hljs-built_in">local</span> $( awk <span class="hljs-string">'BEGIN{ print "AA=100 BB=*" }'</span> )
<span class="hljs-built_in">echo</span> <span class="hljs-string">"<span class="hljs-variable">$AA</span> : <span class="hljs-variable">$BB</span>"</span>
}
$ f1
<span class="hljs-number">100</span> : *
</code></pre>
<p>shell 의 read 명령과 here document 를 이용한 방법<br>명령치환이 일어나야 하므로 END 구분자를 escape 하면 안됩니다.</p>
<pre><code class="lang-bash">$ IFS=, <span class="hljs-built_in">read</span> AA BB CC <<END
$( awk <span class="hljs-string">'BEGIN{ print "100,,*" }'</span> ) <span class="hljs-comment"># 두 번째는 empty 값</span>
END
$ <span class="hljs-built_in">echo</span> <span class="hljs-string">"<span class="hljs-variable">$AA</span> : <span class="hljs-variable">$BB</span> : <span class="hljs-variable">$CC</span>"</span>
<span class="hljs-number">100</span> : : *
</code></pre>
<p>bash 의 경우 다음과 같은 방법도 가능합니다.</p>
<pre><code class="lang-bash"><span class="hljs-comment"># here string 을 이용</span>
$ IFS=, <span class="hljs-built_in">read</span> AA BB CC <<< $( awk <span class="hljs-string">'BEGIN{ print "100,,*" }'</span> )
$ <span class="hljs-built_in">echo</span> <span class="hljs-string">"<span class="hljs-variable">$AA</span> : <span class="hljs-variable">$BB</span> : <span class="hljs-variable">$CC</span>"</span>
<span class="hljs-number">100</span> : : *
<span class="hljs-comment"># source 명령과 프로세스 치환을 이용</span>
$ <span class="hljs-built_in">source</span> <( awk <span class="hljs-string">'BEGIN{ print "AA=100 BB=*" }'</span> )
$ <span class="hljs-built_in">echo</span> <span class="hljs-string">"<span class="hljs-variable">$AA</span> : <span class="hljs-variable">$BB</span>"</span>
<span class="hljs-number">100</span> : *
</code></pre>
<h4 id="here-document-를-이용한-코드-작성방법">here document 를 이용한 코드 작성방법</h4>
<p>shell 에서 제공되는 <code><<WORD</code> 형식을 이용하는 here document 기능은
문서를 작성할 때 single, double quotes 을 escape 할 필요 없이 자유롭게 사용할 수 있는 장점이 있습니다.
그런데 본문 내에서 기본적으로 <code>$</code> 문자로 시작하는 shell 변수가 확장되기 때문에
awk 스크립트를 작성할 때는 다음과 같이 구분자로 사용되는 단어를 escape 하여
shell 변수 확장을 disable 해줘야 합니다.</p>
<pre><code class="lang-bash"><span class="hljs-comment"># heredoc 은 stdin 에 연결되므로 '-f -' 옵션을 사용 ('-' 는 stdin 을 나타냄)</span>
$ awk <span class="hljs-operator">-f</span> - <<\EOF <span class="hljs-comment"># <<\EOF</span>
BEGIN { ... }
EOF
$ awk <span class="hljs-operator">-f</span> - <<<span class="hljs-string">'ABC'</span> <span class="hljs-comment"># <<'ABC'</span>
BEGIN { ... }
ABC
<span class="hljs-comment"># 파이프 로인해 stdin 이 사용 중이므로 -f /dev/fd/3 를 사용</span>
$ <span class="hljs-built_in">command</span> ... | awk <span class="hljs-operator">-f</span> /dev/fd/<span class="hljs-number">3</span> <span class="hljs-number">3</span><<\EOF
BEGIN { ... }
EOF
</code></pre>
<h4 id="awk-내에서-here-document-작성법">awk 내에서 here document 작성법</h4>
<p>awk 에서 shell 명령문을 작성할 때는 기본적으로 스트링을 이용하므로
heredoc 과같이 개행이 필요한 명령문에서는 직접 newline 문자를 사용해야 합니다.</p>
<pre><code class="lang-bash">$ awk <span class="hljs-string">'BEGIN { # 오류
cmd = "cat <<END
111
222
333
END"
system(cmd)
}'</span>
awk: cmd. line:<span class="hljs-number">2</span>: cmd=<span class="hljs-string">"cat <<END
awk: cmd. line:2: ^ unterminated string
awk: cmd. line:2: cmd="</span>cat <<END
awk: cmd. line:<span class="hljs-number">2</span>: ^ syntax error
---------------------------------------------------
$ awk <span class="hljs-string">'BEGIN {
cmd = "cat <<END\n111\n222\n333\nEND" # 직접 newline 문자를 사용
system(cmd)
}'</span>
<span class="hljs-number">111</span>
<span class="hljs-number">222</span>
<span class="hljs-number">333</span>
</code></pre>
<p>만약에 shell 에서처럼 heredoc 을 작성하려면 다음과 같이하면 됩니다.</p>
<pre><code class="lang-bash">$ awk <span class="hljs-string">'BEGIN {
cmd = "cat <<END\n\
${SHELL}\n\
${PWD}\n\
END"
system(cmd)
}'</span>
/bin/bash <span class="hljs-comment"># export 된 값으로 실질적으로는 sh 에의해 실행됩니다.</span>
/home/mug896/tmp
$ awk <span class="hljs-string">'BEGIN {
cmd = "cat <<\\END\n\
${SHELL}\n\
${PWD}\n\
END"
system(cmd)
}'</span>
<span class="hljs-variable">${SHELL}</span>
<span class="hljs-variable">${PWD}</span>
</code></pre>
<h4 id="printf-문에서-천-단위-콤마-넣기">printf 문에서 천 단위 콤마 넣기</h4>
<p>awk 는 스크립트 내에서 필드 변수에 <code>$</code> 문자를 사용하기 때문에 shell 변수로 해석되는 것을
방지하기 위해 single quotes 을 이용해 작성합니다.
그런데 printf 문에서 천 단위 콤마를 넣을 때 사용하는 <code>%'d</code>
포멧 스트링의 경우 <code>'</code> 가 사용되어 문제가 되는데요.
이때는 <code>\047</code> escape 문자를 사용하거나 스크립트 작성에 사용된 single quotes 을 분리한 후에
<code>\'</code> 나 <code>"'"</code> 를 이용해 연결하면 됩니다.</p>
<pre><code class="lang-bash"><span class="hljs-built_in">echo</span> $(<span class="hljs-built_in">echo</span> <span class="hljs-number">2</span>^<span class="hljs-number">64</span> | bc) | LC_ALL=en_US.UTF-<span class="hljs-number">8</span> awk <span class="hljs-string">'{ printf "%'</span>d\n<span class="hljs-string">", <span class="hljs-variable">$1</span> }' # Error
> ^C
$ echo <span class="hljs-variable">$(echo 2^64 | bc)</span> | LC_ALL=en_US.UTF-8 awk '{ printf "</span>%\<span class="hljs-number">047</span>d\n<span class="hljs-string">", <span class="hljs-variable">$1</span> }' # OK
18,446,744,073,709,551,616
$ echo <span class="hljs-variable">$(echo 2^64 | bc)</span> | LC_ALL=ko_KR.UTF-8 awk '{ printf "</span>%<span class="hljs-string">'\'</span><span class="hljs-string">'d\n", $1 }'</span> <span class="hljs-comment"># OK</span>
<span class="hljs-number">18</span>,<span class="hljs-number">446</span>,<span class="hljs-number">744</span>,<span class="hljs-number">073</span>,<span class="hljs-number">709</span>,<span class="hljs-number">551</span>,<span class="hljs-number">616</span>
$ <span class="hljs-built_in">echo</span> $(<span class="hljs-built_in">echo</span> <span class="hljs-number">2</span>^<span class="hljs-number">64</span> | bc) | LC_ALL=ko_KR.UTF-<span class="hljs-number">8</span> awk <span class="hljs-string">'{ printf "%'</span><span class="hljs-string">"'"</span><span class="hljs-string">'d\n", $1 }'</span> <span class="hljs-comment"># OK</span>
<span class="hljs-number">18</span>,<span class="hljs-number">446</span>,<span class="hljs-number">744</span>,<span class="hljs-number">073</span>,<span class="hljs-number">709</span>,<span class="hljs-number">551</span>,<span class="hljs-number">616</span>
.....................................................................
$ awk <span class="hljs-string">'
BEGIN {
if ( "pidof chrome | awk \047{ print NF }\047" | getline count )
print "total chrome pids : " count
}'</span>
total chrome pids : <span class="hljs-number">45</span>
$ awk <span class="hljs-string">'
BEGIN {
if ( "pidof chrome | awk '</span>\<span class="hljs-string">''</span>{ <span class="hljs-built_in">print</span> NF }<span class="hljs-string">'\'</span><span class="hljs-string">'" | getline count )
print "total chrome pids : " count
}'</span>
total chrome pids : <span class="hljs-number">45</span>
</code></pre>
<h4 id="include-할-수-있다">include 할 수 있다</h4>
<p><code>@include</code> 키워드 와 <code>-i</code> 명령 옵션을 이용해 스크립트 파일을 include 해 사용할 수 있습니다.
이 기능은 awk 스크립트 파일을 라이브러리 용도로 활용하기 위한 것으로
한번 include 되어 실행되면 이후에 중복 include 가 되어도 다시 실행되지 않습니다.</p>
<p>파일을 찾을 때는 <code>AWKPATH</code> 환경 변수를 이용하는데 다음과 같이 직접 경로를 지정할 수도 있습니다. </p>
<blockquote>
<p>@include "../test1"<br>@include "/home/abc/awklib/test2" </p>
</blockquote>
<pre><code class="lang-bash">$ cat <span class="hljs-built_in">test</span>1.awk
BEGIN {
<span class="hljs-built_in">print</span> <span class="hljs-string">"This is script test1."</span>
}
@include <span class="hljs-string">"test2"</span>
.................................
$ cat <span class="hljs-built_in">test</span>2.awk
BEGIN {
<span class="hljs-built_in">print</span> <span class="hljs-string">"This is script test2."</span>
}
.................................
$ awk -i <span class="hljs-built_in">test</span>1 <span class="hljs-string">'BEGIN{ print "this is main" }'</span>
This is script <span class="hljs-built_in">test</span>1.
This is script <span class="hljs-built_in">test</span>2.
this is main
</code></pre>
<p><a name="timeout"></a></p>
<h4 id="timeout-설정-방법">timeout 설정 방법</h4>
<p>awk 는 blocking read 에 대해서
millisecond 단위로 timeout 을 설정할 수 있습니다.
이것은 PROCINFO 변수에 값을 설정하는 것으로 이루어지며
개별 operation 별로 설정할 수가 있습니다.
input 값이 도착하지 않아 timeout 이 되면 blocking 이 해제되고 <code>-1</code> 이 반환 됩니다.
이때 ERRNO 변수값도 함께 설정됩니다.</p>
<blockquote>
<p>PROCINFO[ "input_name", "READ_TIMEOUT" ] = timeout in milliseconds</p>
</blockquote>
<pre><code class="lang-bash"><span class="hljs-comment"># timeout 이 되면 getline 에서 -1 이 반환됩니다.</span>
$ awk <span class="hljs-string">'BEGIN {
PROCINFO["/dev/stdin", "READ_TIMEOUT"] = 5000 # 5초
printf "enter number : "
while (getline var < "/dev/stdin" > 0) {
print "entered: " var
printf "enter number : "
}
print "ERRNO: " ERRNO
}'</span>
enter number : <span class="hljs-number">111</span>
entered: <span class="hljs-number">111</span>
enter number : <span class="hljs-number">222</span>
entered: <span class="hljs-number">222</span>
enter number : ERRNO: Connection timed out
</code></pre>
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