linux下crontab中%的使用
crontab中下面的脚本不能
0 1 * * * (cd /u01/prod; rsync -avz app 192.168.0.192:/u01/prod/) &>/home/applprod/backuplog/rsync_`date +%Y%m%d_%H%M%s`.log
执行的时候，/var/log/messages日志中显示：
Sep 22 22:50:01 ebsapp CROND[13389]: (applprod) CMD ((cd /u01/prod; rsync -avz app 192.168.0.192:/u01/prod/) &>/home/applprod/backuplog/rsync_`date +)
好像是命令被截断的样子。
于是我把要执行的命令都封装到一个脚本中，放到crontab中执行。
但是稍后查看crontab的manpage时发现，%在crontab中有特殊含义：
The sixth field (the rest of the line) specifies the command to be run. The entire command portion of the line, up to a new-
line or % character, will be executed by /bin/sh or by the shell specified in the SHELL variable of the cronfile. 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.到这里问题已经清楚了，并不是crontab命令被截断，而是被理解成另外的含义了，解决的方法也有了，就是将%进行转义，修改之后的脚本变成了：
03 23 * * * (cd /u01/prod; rsync -avz app 192.168.0.192:/u01/prod/) &>/home/applprod/backuplog/rsync_`date +\%Y\%m\%d_\%H\%M\%s`.log
