shell脚本中使用if和bc比较变量值和指定值

##【预备知识】
假如我有个日志文件，每天会往里追加。日志摘要如下——
2018-06-12 09:08:56,105 - hdfs.client - INFO - Renaming ‘/apps/wps_prt_feature/business_info/2018-06-11/android_app.temp-1528765731’ to ‘/apps/wps_prt_feature/business_info/2018-06-11/android_app’.
… …
2018-06-12 09:09:29,392 - hdfs.client - INFO - Renaming ‘/apps/wps_prt_feature/business_info/2018-06-11/ios_app.temp-1528765764’ to ‘/apps/wps_prt_feature/business_info/2018-06-11/ios_app’.

我想在里面找到带有当天日期和Renaming字样的内容，以便确认我跑的作业成功了，
那么我就想用shell脚本从日志文件中过滤出来。如何实现呢？下面是思考的过程——

[tony@test-host-10 business_info]$ today=`date +%F`	# 获取当天日期
[tony@test-host-10 business_info]$ echo $today 
2018-05-24

从包含当天日期的日志记录中进一步筛选出含有Renaming的日志

[tony@test-host-10 business_info]$ grep $today log_fifth | grep Renaming | wc -l
2
[tony@test-host-10 business_info]$ renamed_hdfsFile_result=`grep $today log_fifth | grep Renaming | wc -l`
[tony@test-host-10 business_info]$ echo $renamed_hdfsFile_result 
2

经过bc计算,如果true(有2行含有Renaming的记录)则输出1，否则输出0

[tony@test-host-10 business_info]$ echo "$renamed_hdfsFile_result == 2" | bc
1

在linux shell中测试一下脚本

[tony@test-host-10 business_info]$ if [ `echo "$renamed_hdfsFile_result == 2" | bc` -eq 1 ]; then echo "OK~"; else echo "BAD"; fi
OK~

测试成功后，就可以把我们的业务逻辑写入到脚本里了
[tony@test-host-10 business_info]$ cat check_hdfs_dir.sh

#!/bin/bash

today=`date +%F`
renamed_hdfsFile_result=`grep $today log_fifth | grep Renaming | wc -l`
if [ `echo "$renamed_hdfsFile_result == 2" | bc` -eq 1 ]
then
  echo "Successfully renamed android_app and ios_app on our HDFS ^_^"
else
  echo "Not good!"
fi

---

##【需求场景】
我想要在整点时间运行某脚本，但是不想使用crontab。比如我想在上午9点开始运行脚本，需要从date时间中获取小时数，再和9比较，如果大于等于9则开始执行脚本。这里用到了bc来比较数值大小。
如果没有安装bc，需要以root用户使用yum install -y bc即可安装，安装后就能直接使用了。示例脚本如下。

#!/bin/bash

function run_daily_job(){
  yesterday=`date -d"1 days ago" +%Y-%m-%d`
  now_hour=`date | awk -F":" '{print $1}' | awk '{print $5}'`
  echo "Present hour number is____${now_hour}"
  # 判断当前hour是不是9点或9点以后
  if [ `echo "${now_hour} >= 9" | bc` -eq 1 ]; then
    echo "Now it's $1"
    echo Starting processing data on ${yesterday}
    # DO WHAT YOU WANT HERE.
    if [ $? -eq 0 ]; then
      echo 
      echo "0=}========> Job finished."
      exit 0
    else
      echo "Something wrong while running job."
      exit -1
    fi
  
  else
    current=$1
    echo "Current time is ${current}, not the right time(09:00) to run job. Wait another 30 minutes ..."
    sleep 30m

  fi
}

while (true); do
  current_time=`date +"%Y-%m-%d %H:%M:%S"`
  # 此处传参一定要加双引号，否则run_daily_job()中的echo "Current time is ${current} ..." 只会显示年月日,不显示时分秒
  run_job "$current_time"
done

现在是下午14:29，此时运行脚本，输出结果是——

Present hour number is____14
Now it’s 2018-05-24 14:29:57
Starting processing data on 2018-05-23

0=}========> Job finished.

##【延伸】加强脚本的健壮性

如果无法获取到now_hour，脚本就失效了。所以，为了保证能在9点钟运行我的脚本，需要在没有获取到now_hour变量值的情况下给一个默认值。读者可以自己在上面脚本里加一行，加在引用now_hour之前的语句即可。
加之前，可以自己验证一下，我这边验证过了，请看——
【若变量hour为空，则用 :- 给一个默认值】

[tony@test-host-10 business_info]$ hour=''  #此时hour为空
[tony@test-host-10 business_info]$ echo $hour 

[tony@test-host-10 business_info]$ hour=${hour:-9}   #hour变量为空，则 :- 给一个默认值9
[tony@test-host-10 business_info]$ echo $hour 
9
[tony@test-host-10 business_info]$ hour2=${hour2:-15}   #hour2变量为空，则 :- 给一个默认值15
[tony@test-host-10 business_info]$ echo $hour2 
15 

好了就写到这里，看官们觉得涨知识了，请在文章点个赞 ^_