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This article mainly introduces "what is the special significance of% in linux system crontab". In daily operation, I believe that many people have doubts about the special significance of% in linux system crontab. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful for you to answer the doubts of "what is the special significance of% in linux system crontab?" Next, please follow the editor to study!

% usage in crontab under linux

The following script in crontab cannot

01 * (cd / u01ActionProd; rsync-avz app 192.168.0.192:/u01/prod/) & > / home/applprod/backuplog/rsync_ `date +% Y% m% dwells% H% M% S`.log

When executed, the / var/log/messages log shows:

Sep 22 22:50:01 ebsapp CROND [13389]: (applprod) CMD ((cd / u01 date prod; rsync-avz app 192.168.0.192:/u01/prod/) & > / home/applprod/backuplog/rsync_ `date +)

It looks like the order has been cut off.

So I encapsulated all the commands to be executed in a script and executed them in crontab.

But when you look at crontab's manpage later, you find that% has a special meaning in crontab:

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.

At this point, the problem is clear. The crontab command is not truncated, but it is understood as another meaning, and the solution is to escape%, and the modified script becomes:

03 23 * (cd / u01 forward; rsync-avz app 192.168.0.192:/u01/prod/) & > / home/applprod/backuplog/rsync_ `date +\% Y\% m\% d _\% H\% M\% S`.log, the study on "what is the special significance of% in linux system crontab" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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