当直接重定向并由cron运行时，Bash脚本输出会有所不同

Question

我已经编写了以下Bash脚本

TIME=$( date '+%F %H:%M:%S')
MYRUNLEVEL=$(runlevel | cut -d ' ' -f2)

printf "Script started  successfully at  $TIME"
printf ",    Runlevel is $MYRUNLEVEL"
printf "\n"

当我从我的终端运行脚本时，就像这样

$ backup_script.sh >> test_output.txt
$ cat test_output.txt 
Script started  successfully at  2020-04-12 14:53:19,    Runlevel is 5

我正确地写出了运行级。但是当我从cronjob运行脚本时，运行级并没有写出来：

Crontab语法：

 * * * * * /home/philip//bin/backup_script.sh >> /home/philip/LinuxMint/Test_script/cron_output

文件cron_output中的输出：

Script started  successfully at  2020-04-12 14:48:01,    Runlevel is
Script started  successfully at  2020-04-12 14:49:01,    Runlevel is
Script started  successfully at  2020-04-12 14:50:01,    Runlevel is
Script started  successfully at  2020-04-12 14:51:01,    Runlevel is
Script started  successfully at  2020-04-12 14:52:01,    Runlevel is
Script started  successfully at  2020-04-12 14:53:01,    Runlevel is
Script started  successfully at  2020-04-12 14:54:01,    Runlevel is
Script started  successfully at  2020-04-12 14:55:01,    Runlevel is
Script started  successfully at  2020-04-12 14:56:02,    Runlevel is

Answer 1

我的猜测是MYRUNLEVEL=$(runlevel | cut -d ' ' -f2)中的cut -d ' ' -f2使输出为空。试着只使用MYRUNLEVEL="$(runlevel)"，看看你是否得到了你想要的。:)

Answer 2

问题已解决：

以cronjob身份运行脚本未找到runlevel命令。通过将完整路径添加到runlevel解决了这个问题

#!/bin/bash
TIME=$( date '+%F %H:%M:%S')
MYRUNLEVEL=$(/sbin/runlevel | cut -d ' ' -f2)

printf "Script started  successfully at  $TIME"
printf ",    Runlevel is $MYRUNLEVEL "

crontab语法：

* * * * * /home/philip//bin/backup_script.sh >> /home/philip/LinuxMint/Test_script/cron_output

以cron_output格式提供输出：

Script started  successfully at  2020-04-13 16:04:01,    Runlevel is 5