Detailed explanation of comparison of python and bash versions of small programs

最近有一个小需求：在一个目录下有很多文件，每个文件的第一行是BEGIN开头的，最后一行是END开头的，中间每一行有多列，数量不等，第一列称为"DN", 第二列称为"CV"，DN和CV的联合作为主键，现在需要检测文件中是否有重复的DN-CV。

于是写了个简单的python程序

#! /usr/bin/python
import os
import sys
cmd = "cat /home/zhangj/hosts/* | grep -v BEGIN | grep -v END"
def check_dc_line():
 has_duplicate = False
 dc_set = set()
 for dc_line in os.popen(cmd, 'r').readlines():
  dc_token = dc_line.split()
  dn = dc_token[0]
  cv = dc_token[1]
  dc = dn + "," + cv
  if dc in dc_set:
   print "duplicate dc found:", dc
   has_duplicate = True
  else:
   dc_set.add(dc)
 return has_duplicate
if not check_dc_line():
    print "no duplicate dc"

对于250个文件，共60万行的数据，过滤一遍约1.67秒

有点不甘心这个效率，于是又写了一个同样功能的shell脚本

#! /bin/bash
cat /home/zhangj/hosts/* | grep -v BEGIN | grep -v END | awk '
 BEGIN {
  has_duplicate = 0
 }
 {
  dc = $1","$2; 
  if (dc in dc_set) 
  {
   print "duplicate dc found", dc 
   has_duplicate = 1
  } 
  else {
   dc_set[dc] = 1
  }
 }
 END {
  if (has_duplicate ==0)
  {
   print "no duplicate dc found"
  }
 }
'

为了进一步比较，重复了10次实验。

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