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Fish_n_Chips avatar Ubuntu

Writing a specific format of time in a text file every minute using Cron

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Fish_n_Chips

I'm rather new to Linux. I recently wanted to learn how to work with Cron. So I wrote the following line to crontab file and it worked:

* * * * * date >> //home/os/system-date.txt

This line will append the current date and time in system-date.txt every minute.

When I run the following command in terminal, time is printed in a specific format:

date +"%H-%M-%S"

For instance, 23-59-59 is printed.

But when I want to do this with Cron, nothing is written in the txt file. To be specific, when I write the following line in crontab

* * * * * date +"%H-%M-%S" >> //home/os/system-date.txt

nothing happens. I wonder why.

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FedKad avatar
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FedKad
You may have a syntax error on the command line. Try to add `2>>/home/os/cron.err` to the end of the crontab entry to see what the error is.
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Fish_n_Chips avatar
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Fish_n_Chips
Thanks. I did but no cron.err file gets created. @FedonKadifeli
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FedKad avatar Ubuntu
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FedKad

You should escape the percent (%) signs in your crontab entries with a backslash (\) like this:

* * * * * date +"\%H-\%M-\%S" >>/home/os/system-date.txt 2>>/home/os/system-date.err

Percent signs have a special meaning in crontab entries: They are interpreted as newline characters. Please, see the man page for crontab(5):

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 "\".

Also, note that the command in a crontab entry will not be executed by /bin/bash normally. So, it is always a good practice to create a Bash script and call that Bash script from crontab. Another point to note is that the PATH environment variable is much simpler in a crontab executed command (or script), so it is again a good practice to use full path names for commands executed in a script which is written to be called by crontab.

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Luuk avatar Ubuntu
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Luuk

Your could create a simple script file (i.e. addDate.sh) like:

#!/bin/bash
date +"%H-%M-%S" 2>&1 >> //home/os/system-date.txt

The 2>&1 redirects errors also to the specified outputfile.

and in your crontab run this script file.

* * * * * /myscripts/addDate.sh

Where /myscripts is the path where you saved your script file.

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