bash 脚本和浮点除法
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Division in script and floating-point
提问by Paris31
I would like to do the following operation in my script:
我想在我的脚本中执行以下操作：
1 - ((m - 20) / 34)
I would like to assign the result of this operation to another variable. I want my script use floating point math. For example, for m = 34:
我想将此操作的结果分配给另一个变量。我希望我的脚本使用浮点数学。例如，对于 m = 34：
results = 1 - ((34 - 20) / 34) == 0.588
回答by John Kugelman
You could use the bccalculator. It will do arbitrary precision math using decimals (not binary floating point) if you set increease scalefrom its default of 0:
你可以用bc计算器。如果将 increease 设置scale为默认值 0 ，它将使用小数（不是二进制浮点）进行任意精度数学运算：
$ m=34
$ bc <<< "scale = 10; 1 - (($m - 20) / 34)"
.5882352942
The -loption will load the standard math library and default the scale to 20:
该-l选项将加载标准数学库并将比例默认为 20：
$ bc -l <<< "1 - (($m - 20) / 34)"
.58823529411764705883
You can then use printf to format the output, if you so choose:
然后，您可以使用 printf 来格式化输出，如果您这样选择：
printf "%.3f\n" "$(bc -l ...)"
回答by jordanm
Bash does not do floating point math. You can use awk or bc to handle this. Here is an awk example:
Bash 不进行浮点数学运算。您可以使用 awk 或 bc 来处理此问题。这是一个 awk 示例：
$ m=34; awk -v m=$m 'BEGIN { print 1 - ((m - 20) / 34) }'
0.588235
To assign the output to a variable:
要将输出分配给变量：
var=$(awk -v m=$m 'BEGIN { print 1 - ((m - 20) / 34) }')
回答by Cyrus
Teach bash e.g. integer division with floating point results:
用浮点结果教 bash 例如整数除法：
#!/bin/bash
div () # Arguments: dividend and divisor
{
if [ -eq 0 ]; then echo division by 0; exit; fi
local p=12 # precision
local c=${c:-0} # precision counter
local d=. # decimal separator
local r=$((/)); echo -n $r # result of division
local m=$(($r*))
[ $c -eq 0 ] && [ $m -ne ] && echo -n $d
[ -eq $m ] || [ $c -eq $p ] && return
local e=$((-$m))
let c=c+1
div $(($e*10))
}
result=$(div 1080 633) # write to variable
echo $result
result=$(div 7 34)
echo $result
result=$(div 8 32)
echo $result
result=$(div 246891510 2)
echo $result
result=$(div 5000000 177)
echo $result
Output:
输出：
1.706161137440
0.205882352941
0.25
123445755
28248.587570621468
回答by siraj md
echo $a/$b|bc -l
gives the result.
给出结果。
Example:
例子：
read a b
echo $a/$b|bc -l
Enter a & b value as 10 3, you get 3.3333333333
输入 a & b 值作为 10 3，你得到 3.3333333333
If you want to store the value in another variable then use the code
如果要将值存储在另一个变量中，请使用代码
read a b
c=`echo $a/$b|bc -l`
echo $c
It also gives the same result as above. Try it...
它也给出了与上面相同的结果。尝试一下...
回答by wmeitzen
I know this is an old thread, but this seemed like a fun project to tackle without using bcor invoking recursion. I'm sure it can be improved, but this maxed out my skill.
我知道这是一个旧线程，但这似乎是一个有趣的项目，无需使用bc或调用递归即可解决。我相信它可以改进，但这最大限度地发挥了我的技能。
numerator=5
denominator=7 # - 0 -> returns "undef"
decimal_places=4 # - 0 -> same as echo $(( $numerator / $denominator ))
_result_sign=""
let _dp_exp=10**decimal_places
if [ $denominator -eq 0 ]; then _div_result_int_large=0; else let _div_result_int_large=$((numerator * _dp_exp / denominator)); fi
if [ $_div_result_int_large -lt 0 ]; then let _div_result_int_large=$(( _div_result_int_large * -1 )); _result_sign="-"; fi
let _div_result_int=$((_div_result_int_large / _dp_exp))
let _div_result_mant=$((_div_result_int_large - _div_result_int * _dp_exp))
let _dp_lzeros=$((decimal_places - ${#_div_result_mant}))
printf -v _div_result_mant_padded "%.${_dp_lzeros}d$_div_result_mant"
div_result="$_result_sign$_div_result_int"
if [ $decimal_places -gt 0 ]; then div_result="$_result_sign$_div_result_int.$_div_result_mant_padded"; fi
if [ $denominator -eq 0 ]; then div_result="undef"; fi
echo $div_result
Example output:
示例输出：
numerator=5
denominator=7
decimal_places=5
-> 0.71428
numerator=250
denominator=13
decimal_places=0
-> 19
numerator=-5
denominator=6
decimal_places=2
-> -0.83
numerator=3
denominator=0 # - uh-oh
decimal_places=2 # - can be anything, in this case
-> undef
回答by minttux
Use this script open this file with favorite editor like:
使用此脚本使用最喜欢的编辑器打开此文件，例如：
$ sudo vim /usr/bin/div
Then paste this code:
然后粘贴此代码：
#!/bin/bash
# Author: Danial Rikhteh Garan ([email protected])
if [[ -z "" ]] || [[ -z "" ]]; then
echo "Please input two number"
echo "for 100/50 use: div 10 50"
exit 1;
fi
div=$(echo "/" | bc -l);
echo 0$div | sed 's/[0]*$//g'
Now chmod it to 755:
现在将其修改为 755：
$ sudo chmod 755 /usr/bin/div
Now use it:
现在使用它：
$ div 5 100
0.05
In your script you can use this:
在你的脚本中，你可以使用这个：
var=$(div 5 100);
echo "$var"
