计数器增量猛砸循环不工作 [英] Counter increment in Bash loop not working

问题描述

我在那里我运行一个循环以下简单的脚本，并希望保持一个 COUNTER 。我无法弄清楚为什么计数器不更新。它是由于子shell这就是越来越产生的？我怎么可能会解决这个问题？

 ＃！/斌/庆典WFY_PATH =在/ var /日志/ n​​ginx的
WFY_FILE = error.log中
COUNTER = 0
grep的GET / LOG_'$ WFY_PATH / $ WFY_FILE | grep的上游超时| awk的-F'，''{打印$ 2，$ 4，$ 0}'| AWK'{打印http://domain.com$ 5＆安培; IP =$ 2＆放大器;日期=$ 7＆放大器;时间=$ 8＆放大器;年底= 1}'| awk的-F'和末端= 1''{打印$ 1＆安培;年底= 1}'|
（
而读WFY_URL
做
    回声$ WFY_URL #Some更多行动
    COUNTER = $（（COUNTER + 1））
DONE
）回声$＃COUNTER输出= 0
 

解决方案

首先，你是不是增加了柜台。更改 COUNTER = $（（COUNTER））到 COUNTER = $（（COUNTER + 1））或 COUNTER = $ [COUNTER + 1] 将增加。

第二，它是棘手，你揣到后台传播子shell变量被调用者。在子shell变量不可用子shell之外。这些都是局部变量的子进程。

解决这个问题是使用临时文件存储的中间值的一种方式：

  TEMPFILE =的/ tmp / $$。TMP
呼应0 GT; $ TEMPFILE＃环放在这里
  ＃获取的价值，增加其
  COUNTER = $ [$（猫$ TEMPFILE）+ 1]  ＃存储新值
  回声$ COUNTER＆GT; $ TEMPFILE＃循环中完成，脚本完成，删除文件
断开链接$ TEMPFILE
 

I have the following simple script where I am running a loop and want to maintain a COUNTER. I am unable to figure out why the counter is not updating. Is it due to subshell thats getting created? How can I potentially fix this?

#!/bin/bash

WFY_PATH=/var/log/nginx
WFY_FILE=error.log
COUNTER=0
grep 'GET /log_' $WFY_PATH/$WFY_FILE | grep 'upstream timed out' | awk -F ', ' '{print $2,$4,$0}' | awk '{print "http://domain.com"$5"&ip="$2"&date="$7"&time="$8"&end=1"}' | awk -F '&end=1' '{print $1"&end=1"}' |
(
while read WFY_URL
do
    echo $WFY_URL #Some more action
    COUNTER=$((COUNTER+1))
done
)

echo $COUNTER # output = 0

解决方案

First, you are not increasing the counter. Changing COUNTER=$((COUNTER)) into COUNTER=$((COUNTER + 1)) or COUNTER=$[COUNTER + 1] will increase it.

Second, it's trickier to back-propagate subshell variables to the callee as you surmise. Variables in a subshell are not available outside the subshell. These are variables local to the child process.

One way to solve it is using a temp file for storing the intermediate value:

TEMPFILE=/tmp/$$.tmp
echo 0 > $TEMPFILE

# Loop goes here
  # Fetch the value and increase it
  COUNTER=$[$(cat $TEMPFILE) + 1]

  # Store the new value
  echo $COUNTER > $TEMPFILE

# Loop done, script done, delete the file
unlink $TEMPFILE

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