Bash循环中的计数器增量不起作用 [英] Counter increment in Bash loop not working

问题描述

我有以下简单的脚本，我在其中运行一个循环并希望维护一个 COUNTER.我无法弄清楚为什么计数器没有更新.是因为创建了子shell吗?我该如何解决这个问题?

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

推荐答案

首先，您没有增加计数器.将 COUNTER=$((COUNTER)) 更改为 COUNTER=$((COUNTER + 1)) 或 COUNTER=$[COUNTER + 1]会增加.

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

其次，将子shell 变量反向传播给被调用者是比较棘手的.子外壳中的变量在子外壳之外不可用.这些是子进程的局部变量.

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.

一种解决方法是使用临时文件来存储中间值:

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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