如何在 Bash 脚本中添加数字? [英] How can I add numbers in a Bash script?

问题描述

我有这个 Bash 脚本，但我在第 16 行遇到了问题.如何获取第 15 行的先前结果并添加到第 16 行的变量?

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?

#!/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

推荐答案

对于整数:

• 使用算术展开:$((EXPR))

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

使用外部 expr 实用程序.请注意，这仅适用于非常旧的系统.

Using the external expr utility. Note that this is only needed for really old systems.

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

对于浮点:

Bash 不直接支持这一点，但您可以使用一些外部工具:

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

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

您也可以使用科学记数法(例如，2.5e+2).

You can also use scientific notation (for example, 2.5e+2).

常见陷阱:

• 设置变量时，=两边不能有空格，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)

• 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 (for example, num= or num)

num=1 num =2

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.他们不能处理像 3+ +4 这样的参数.

bc and expr expect each number and operator as a separate argument, so whitespace is important. They cannot process arguments like 3+ +4.

num=`expr $num1+ $num2`

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