/ usr / local / newsbin / tại 2:30 AM vào các buổi sáng thứ Bảy và Chủ Nhật. Ba mục cuối cùng hoạt động minh họa đến ba lựa chọn thay thế xử lý đầu ra: chuyển hướng nó vào một tập tin, đường ống qua đường bưu điện, và loại bỏ nó vào / dev / null. | The sixth entry executes the C shell script usr local etc monthly at 3 30 . on the first day of each month. Notice that the command format specifically the output redirection uses Bourne shell syntax even though the script itself will be run under the C shell. Were it not disabled the final entry would run the command usr local newsbin at 2 30 . on Saturday and Sunday mornings. The final three active entries illustrate three output-handling alternatives redirecting it to a file piping it through mail and discarding it to dev null . If no output redirection is performed the output is sent via mail to the user who ran the command. The command field can be any Unix command or group of commands properly separated with semicolons . The entire crontab entry can be arbitrarily long but it must be a single physical line in the file. If the command contains a percent sign cron will use any text following this sign as standard input for command . Additional percent signs can be used to subdivide this text into lines. For example the following crontab entry 30 11 31 12 usr bin wall Happy New Year Let s make it great runs the wall command at 11 30 . on December 31 using the text Happy New Year Let s make it great as standard input. Note that the day of the week and day of the month fields are effectively ORed if both are filled in the entry is run on that day of the month and on matching days of the week. Thus the following entry would run on January 1 and every Monday 1 1 1 usr local bin test55 In most implementations the cron daemon reads the crontab files when it starts up and whenever there have been changes to any of the crontab files. In some generally older versions cron reads the crontab files once every minute. The BSD crontab file etc crontab uses a slightly different entry format inserting an additional field between the weekday and command fields the user account that should be used to run the specified command. Here is a sample entry that .
