如何使用 bash shell 计算功率值
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how to compute power value with bash shell
提问by Eman
We want to calculate 2^(3.0) and 2^(-3.0). thanks.
我们要计算 2^(3.0) 和 2^(-3.0)。谢谢。
!/bin/bash
c=3.0
g=-3.0
c=$((2**$c)) #syntax error: invalid arithmetic operator (error token is ".0")
g=$((2**$g)) #syntax error: invalid arithmetic operator (error token is ".0")
echo "c=$c"
echo "g=$g"
回答by Keith Thompson
Bash's built-in arithmetic only operates on integers, and doesn't allow a negative exponent for the **operator.
Bash 的内置算术只对整数进行运算，并且不允许**运算符使用负指数。
There are a variety of other tools available that can perform floating-point arithmetic. For example:
有多种其他工具可以执行浮点运算。例如：
$ c=3.0
$ g=-3.0
$ awk "BEGIN{print $c ** $c}"
27
$ awk "BEGIN{print $c ** $g}"
0.037037
$ perl -e "print $c ** $c, qq(\n), $c ** $g, qq(\n)"
27
0.037037037037037
To store the result in a variable:
要将结果存储在变量中：
$ c=$(awk "BEGIN{print $c ** $c}")
$ echo $c
27
回答by Thamme Gowda
Good answers already in the thread using perl and awk. We can also use python:
使用 perl 和 awk 的线程中已经有很好的答案。我们也可以使用python：
python -c "from sys import argv as a; print(pow(int(a[1]), int(a[2])))" 2 6
For reuse:
重用：
alias pow='python -c "from sys import argv as a; print(pow(int(a[1]), int(a[2])))"'
pow 2 6
pow 2 -2
回答by James White
#!/bin/bash
for (( i=1; i<257; i++ ))
do
h=`echo 2^"$i" |bc -l`;
echo -e -n $i " " '\t'
echo $h |tr -d -c [0-9] |rev |sed -e 's/\([0-9][0-9][0-9]\)/,/g' |rev | sed 's/^,//';
done
exit 0
