Bash脚本统计交易日志股票交易数异常：IBM计数少1

需求说明 #

• 统计交易日志中各股票Symbol的交易次数，按交易次数降序排列，每行对应一笔交易。
• 输入日志每行格式：Datetime(YYYYMMDDHHMMSS), Stock, Symbol, BUY/SELL, Quantity, Price

输入输出示例 #

示例输入 #

Datetime(YYYYMMDDHHMMSS), Stock, Symbol, BUY/SELL, Quantity, Price
20190102091055,IBM,BUY,1.160
20190102091058,BABA,SELL,10,155
20190102091059,IBM,BUY,2,159

预期输出 #

IBM 2
BABA 1

现有脚本 #

#!/bin/bash

declare -A symbols  # Declare an associative array to store the symbols and their counts

# Read input line by line
while read line
do
  # Extract the stock symbol from the line
  symbol=$(echo "$line" | cut -d',' -f2)

  # If the symbol already exists in the array, increment its count
  # Otherwise, add the symbol to the array with a count of 1
  if [[ ${symbols[$symbol]+_} ]]; then
    symbols[$symbol]=$((symbols[$symbol]+1))
  else
    symbols[$symbol]=1
  fi
done < "${1:-/dev/stdin}" # Read input from stdin or from a file specified as a command-line argument

# Sort the symbols and their counts in descending order of count
for symbol in "${!symbols[@]}"
do
  echo "$symbol ${symbols[$symbol]}"
done | sort -rnk2

问题现象 #

测试输入中IBM预期交易次数为27，但脚本输出为26，其余股票计数正确。

测试输入（截断版） #

20190527200918,AMZN,SELL,32,1830
20190527200918,AMZN,BUY,26,1827
20190527200918,IBM,SELL,12,139
20190527200918,IBM,SELL,93,144
20190527200918,IBM,SELL,6,141
20190527200918,AMZN,BUY,44,1833
20190527200918,GOOG,SELL,77,1145
20190527200918,GOOG,BUY,89,1135
20190527200918,IBM,BUY,21,139
20190527200918,AMZN,BUY,89,1834
20190527200918,IBM,SELL,80,139
20190527200918,MSFT,SELL,48,135
20190527200918,MSFT,BUY,66,131
20190527200918,MSFT,SELL,21,141
20190527200918,AMZN,SELL,5,1826
20190527200918,MSFT,BUY,47,141
20190527200918,AMZN,SELL,19,1833
20190527200918,AMZN,BUY,22,1831
20190527200918,IBM,BUY,75,139
20190527200918,GOOG,BUY,70,1141
20190527200918,AAPL,SELL,43,182
20190527200918,MSFT,BUY,7,136
20190527200918,GOOG,SELL,89,1147
20190527200918,AMZN,SELL,54,1828
20190527200918,AAPL,SELL,7,189
20190527200918,MSFT,SELL,66,136
20190527200918,AAPL,SELL,31,189
20190527200918,IBM,BUY,39,137
20190527200918,MSFT,SELL,10,128
20190527200918,IBM,BUY,15,146
20190527200918,IBM,SELL,38,133
20190527200918,IBM,SELL,76,146
20190527200918,G{-truncated-}

脚本输出 #

IBM 26
MSFT 22
AMZN 21
GOOG 17
AAPL 13

预期输出 #

IBM 27
MSFT 22
AMZN 21
GOOG 17
AAPL 13

问题排查与修复 #

问题根源 #

原脚本使用while read line读取输入时，若文件最后一行没有换行符，read会返回非零状态码，导致该行被跳过不处理。测试输入的最后一行恰好是截断行且无换行符，这正是IBM计数少1的原因。此外，原脚本的计数逻辑可以简化，还可添加表头跳过、空Symbol过滤的逻辑增强鲁棒性。

修复后的脚本 #

#!/bin/bash

declare -A symbols

# 读取所有行，包括无换行符的最后一行
while IFS= read -r line || [ -n "$line" ]; do
  # 跳过表头行（如果输入包含表头）
  if [[ "$line" == Datetime* ]]; then
    continue
  fi
  # 提取第二个字段作为Symbol
  symbol=$(echo "$line" | cut -d',' -f2)
  # 仅对非空Symbol计数
  if [[ -n "$symbol" ]]; then
    ((symbols[$symbol]++))
  fi
done < "${1:-/dev/stdin}"

# 按交易次数降序输出
for symbol in "${!symbols[@]}"; do
  echo "$symbol ${symbols[$symbol]}"
done | sort -rnk2

关键优化点 #

1. 处理无换行符的最后一行：while IFS= read -r line || [ -n "$line" ]确保即使最后一行没有换行符，只要内容非空就会被处理。
2. 简化计数逻辑：((symbols[$symbol]++))无需判断Symbol是否已存在，Bash会自动将不存在的数组元素初始化为0后自增。
3. 增强鲁棒性：添加表头跳过逻辑和空Symbol过滤，避免无效数据干扰统计。

内容的提问来源于stack exchange，提问作者julia lum