crontab里的特殊符号%导致命令不能执行

有群里的小伙伴说crontab里的任务不执行，具体是这样的

*/1 * * * * /bin/date "+%Y-%m-%d %H:%M:%S" >>/data/tmp/test.log

我试了下在命令行可以执行，定时任务确实不执行，于是去翻了下日志：

#tail -f /var/spool/mail/root
X-Cron-Env: <HOME=/root>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=root>
X-Cron-Env: <USER=root>
Message-Id: <20200108081701.8FD502100481@D3L40.localdomain>
Date: Wed,  8 Jan 2020 16:17:01 +0800 (CST)

/bin/sh: -c: line 0: unexpected EOF while looking for matching `"'
/bin/sh: -c: line 1: syntax error: unexpected end of file

From root@D3L40.localdomain  Wed Jan  8 16:18:01 2020

说是语法错误，结尾不对，明明是两个双引号啊，这样就有可能是里面有特殊字符导致命令意外中断了，于是查了下万能的百度发现：

The “sixth” field (the rest of the line) specifies the command to be run. The entire command portion of the line, up to a newline or % character, will be executed by /bin/sh or by the shell specified in the SHELL variable of the crontab file. Percent-signs (%) in the command, unless escaped with backslash (), will be changed into newline characters, and all data after the first % will be sent to the command as standard input. There is no way to split a single command line onto multiple lines, like the shell’s trailing “”.

大概是在crontab里%当换行符用了，想要正常使用就得加反引号\，\%这样来用。

于是把命令改成了：

*/1 * * * * /bin/date "+\%Y-\%m-\%d \%H:\%M:\%S" >>/data/tmp/test.log

最后：

# cat test.log
2020-01-08 16:38:01
2020-01-08 16:39:01

可以了，于是想着记一下，好记性不如烂笔头嘛。