bash 大数据脚本优化

Question

I have the follogwing litte Skript that forms date. The Problem i face is that the Skript is used for big data log files and it takes far to long. I changed the for loop from read to cat because its faster. But the data program is still far to slow. How can I improve this?

IFS='
'
for i in $(cat ist.log | egrep -o "^.{19}"); do 
        olddatum=${i}
        newdatum=`date -d "${olddatum}" +'%b %e %T'`
        echo ${newdatum} >> soll.log.fixed
done

Answer 1

With the shell and sed and the date utility (most probably GNU date )

#!/bin/sh

search=$(sed "s/^\(.\{19\}\).*/\1/" file.txt)
replace=$(date -d "$search" '+%b %e %T')
sed "s/^$seach/$replace /" file.txt

---

With a while read loop using the shell. Don't read lines with for

#!/usr/bin/env bash

while IFS= read -r lines; do
 if [[ $lines =~ ^(.{19})(.+) ]]; then
   printf '%s %s\n' "$(date -d "${BASH_REMATCH[1]}" +'%b %e %T')" "${BASH_REMATCH[2]}"
 else
   printf '%s\n' "$lines"
 fi
done < file.txt