shell算术运算
<h3>1、bc计算</h3><p></p><pre class="brush:bash;toolbar:false">bc_test=`echo “10 + 1″ | bc`
file_size=`echo “${data_size[“${i}”]} + ${index_size[“${i}”]}” | bc`</pre><p>根据不同系统可能遇到如下错误</p><pre class="brush:bash;toolbar:false">(standard_in) 1: illegal character: N
(standard_in) 1: illegal character: U
(standard_in) 1: illegal character: L
(standard_in) 1: illegal character: L
(standard_in) 1: syntax error
(standard_in) 1: illegal character: N
(standard_in) 1: illegal character: U
(standard_in) 1: illegal character: L
(standard_in) 1: illegal character: L</pre><p></p>
<h3>2、expr计算</h3>
<p></p><pre class="brush:bash;toolbar:false">expr_text=`expr 1 + 1`
file_size=`expr ${data_size[“${i}”]} + ${index_size[“${i}”]}`</pre><p>可能遇到错误如下</p><pre class="brush:bash;toolbar:false">expr: non-integer argument</pre><p></p>
<h3>3、$(( ))计算</h3>
<p></p><pre class="brush:bash;toolbar:false">file_size=$((${data_size[“${i}”]} + ${index_size[“${i}”]}))</pre><p>并且可以进行进制转换<br>
十六进制转十进制：</p><pre class="brush:bash;toolbar:false">$ ((num=0xff));
$ echo $num;
255
$ ((num=16#ff));
$ echo $num;
255</pre><p>base-32转十进制：</p><pre class="brush:bash;toolbar:false">$ ((num=32#ffff));
$ echo $num;
507375</pre><p>base64转十进制：</p><pre class="brush:bash;toolbar:false">$ ((num=64#abc_));
$ echo $num;
2667327</pre><p>二进制转十进制</p><pre class="brush:bash;toolbar:false">$ ((num=2#11111111));
$ echo $num;
255</pre><p>十进制转八进制<br>
这里使用到：bc外部命令完成。bc命令格式转换为：echo “obase=进制;值”|bc</p><pre class="brush:bash;toolbar:false">$ echo “obase=8;01234567″|bc
4553207</pre><p>二进制，十六进制，base64转换为 十进制也相同方法。</p><pre class="brush:bash;toolbar:false">$ echo “obase=64;123456″|bc
30 09 00</pre><p> </p>
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