为何Shell脚本未在预期错误场景下触发报错？

当merge_marketable_count数值明显小于marketable_count时，运行以下Shell脚本却未触发错误数组输出和退出状态，不符合预期：

#!/bin/bash

# Sample local values
merge_marketable_count=0
marketable_count=200
countDifference=95/100  # This still assigns the string "95/100" to countDifference. 

merge_opt_out_count=50
opt_out_count=60

total_merge_count=500
total_count=550

errorArray=()

if [ "$merge_marketable_count" -lt "$(( marketable_count * ${countDifference} ))" ]; then
  marketable_message="The total Marketable counts within our EMU table is greater than 5%, merge=$merge_marketable_count, view=$marketable_count and CountDiffUsed=${countDifference}"
  echo $marketable_message
  errorArray+=("$marketable_message")
fi


if [ ${#errorArray[@]} -gt 0 ]; then
  echo "error array"
  echo "${#errorArray[@]}"
  exit 1
fi

1. 字符串赋值导致运算错误：countDifference=95/100只是把字符串"95/100"赋值给变量，不是计算后的0.95。在$(( marketable_count * ${countDifference} ))里，Shell会把"95/100"当作整数除法处理，结果是0（Shell整数除法会直接舍去小数）。此时判断条件变成0 -lt 0，不成立，自然不会触发错误逻辑。
2. Shell整数运算限制：$((...))只支持整数运算，没法直接处理浮点数比较，这也是导致比例计算失效的核心原因。

方案1：用bc处理浮点数比较 #

借助bc工具实现浮点数运算和比较，这样能准确判断比例差异：

#!/bin/bash

# 示例值
merge_marketable_count=0
marketable_count=200
countDifference=0.95  # 直接用小数表示95%的比例

merge_opt_out_count=50
opt_out_count=60

total_merge_count=500
total_count=550

errorArray=()

# 通过bc计算浮点数，返回1表示条件成立，0表示不成立
if [ $(echo "$merge_marketable_count < $marketable_count * $countDifference" | bc -l) -eq 1 ]; then
  marketable_message="EMU表中可营销总数差异超过5%，merge=$merge_marketable_count, view=$marketable_count，使用的差异比例=${countDifference}"
  echo "$marketable_message"
  errorArray+=("$marketable_message")
fi

if [ ${#errorArray[@]} -gt 0 ]; then
  echo "错误数组内容："
  echo "${errorArray[@]}"
  exit 1
fi

方案2：转成整数比例运算（避免浮点数） #

把百分比转换为整数运算，比如95%等价于marketable_count * 95 / 100，用整数运算就能实现需求：

#!/bin/bash

# 示例值
merge_marketable_count=0
marketable_count=200
countDifference=95  # 用整数表示百分比，95即95%

merge_opt_out_count=50
opt_out_count=60

total_merge_count=500
total_count=550

errorArray=()

# 整数运算计算marketable_count的95%，再做比较
if [ "$merge_marketable_count" -lt $(( marketable_count * countDifference / 100 )) ]; then
  marketable_message="EMU表中可营销总数差异超过5%，merge=$merge_marketable_count, view=$marketable_count，使用的差异比例=${countDifference}%"
  echo "$marketable_message"
  errorArray+=("$marketable_message")
fi

if [ ${#errorArray[@]} -gt 0 ]; then
  echo "错误数组内容："
  echo "${errorArray[@]}"
  exit 1
fi

内容的提问来源于stack exchange，提问作者AnthonyEdwardsStan