bash - 如何在bash脚本中添加数字(How can I add numbers in a bash script)

Question

I have this bash script and I had a problem in line 16. How can I take the previous result of line 15 and add it to the variable in line 16?

(我有这个bash脚本，我在第16行遇到了问题。如何获取第15行的先前结果并将其添加到第16行的变量中？)

#!/bin/bash

num=0
metab=0

for ((i=1; i<=2; i++)); do      
    for j in `ls output-$i-*`; do
        echo "$j"

        metab=$(cat $j|grep EndBuffer|awk '{sum+=$2} END { print sum/120}') (line15)
        num= $num + $metab   (line16)
    done
    echo "$num"
 done

  ask by Nick translate from so

Answer 1

For integers :

(对于整数 ：)

• Use arithmetic expansion : $((EXPR))

  (使用算术扩展 ： $((EXPR)))

   num=$((num1 + num2)) num=$(($num1 + $num2)) # also works num=$((num1 + 2 + 3)) # ... num=$[num1+num2] # old, deprecated arithmetic expression syntax 

• Using the external expr utility.

  (使用外部expr实用程序。)

  Note that this is only needed for really old systems.

  (请注意，这仅适用于真正的旧系统。)

   num=`expr $num1 + $num2` # whitespace for expr is important 

---

For floating point :

(对于浮点数 ：)

Bash doesn't directly support this, but there's a couple of external tools you can use:

(Bash并不直接支持这一点，但您可以使用几种外部工具：)

num=$(awk "BEGIN {print $num1+$num2; exit}")
num=$(python -c "print $num1+$num2")
num=$(perl -e "print $num1+$num2")
num=$(echo $num1 + $num2 | bc)   # whitespace for echo is important

You can also use scientific notation (eg: 2.5e+2 )

(您也可以使用科学记数法（例如： 2.5e+2 ）)

---

Common pitfalls :

(常见的陷阱 ：)

• When setting a variable, you cannot have whitespace on either side of = , otherwise it will force the shell to interpret the first word as the name of the application to run (eg: num= or num )

  (设置变量时，你不能在=两边都有空格，否则会强制shell将第一个单词解释为要运行的应用程序的名称（例如： num=或num ）)

  num= 1 num =2

  ( num= 1 num =2 )

• bc and expr expect each number and operator as a separate argument, so whitespace is important.

  (bc和expr期望每个数字和运算符作为单独的参数，因此空格很重要。)

  They cannot process arguments like 3+ +4 .

  (他们无法处理像3+ +4这样的论点。)

  num=`expr $num1+ $num2`