Shell Programming and Scripting

Hello all,

I want to run a script every 5 minutes. How to accomplish this task?


Thanks in advance
Mrudula

cron is your friend.

Cron from the name Chronos (the god of time)

The cron daemon is a long-running process that executes commands at specific dates and times. You can use this to schedule activities, either as one-time events or as recurring tasks


For commands that need to be executed repeatedly (e.g., hourly, daily, or weekly), you can use the crontab command.

The crontab command creates a crontab file containing commands and instructions for the cron daemon to execute. You can use the crontab command with the following options:

crontab filename installs a crontab from the file

crontab -e Edit your crontab file, or create one if it doesn't already exist.

crontab -l Display your crontab file.

A typical crontab will have system maintenance type tasks but any task can be put into cron.

Each entry in a crontab file consists of six fields, specifying in the following order:
minute(s) hour(s) day(s) month(s) weekday(s) command(s)

10 3 * * 0,4 /etc/cron.d/logchecker
10 3 * * 0 /usr/lib/newsyslog
15 3 * * 0 /usr/lib/fs/nfs/nfsfind

Thanks for the wonderful explanation Rob !! Now lemme try to work it out ...

To choice if you want to execute this script for everybody or for a specific user, that don't need to be the logged user like crontab -e, you can edit the file /etc/crontab. This file is similar similar, but there you have more one parameter, that is the user.

I just tried a simple thing - to display time on the terminal every 5 minutes .. this is my crontab entry for it - but it doesnt seem to work ... y is that?

pwd
/usr/lib

contab -e
no crontab for root - using an empty one
crontab: installing new crontab

crontab -l
0,5,10,15,20 * * * * (echo -n ' '; date; echo " ") > /dev/console

I guess yes...
Maybe no permission. If u syntax is wrong, its make a error in "crontab: installing new crontab".

To execute you script every 5 Min, you can use:

*/5 * * * * command

If I use,

*/5 * * * * /home/shahnaz/abc.sh >> /home/shahnaz/abc.log

I get an error saying like

crontab: error on previous line; unexpected character found in line.

Can you say why it was thrown such error?