variables in a cron job not working properly

aristosv · 10-29-2022, 11:20 PM

I have a cronjob running a script every hour. I want it to email me the output, and also write the output to a log file. Both stdout & stderr.

Code:

MAILTO="me@myemail.com"
DATEVAR="date -d '+1 hour' +'\%d_\%m_\%Y_\%H'"
0 * * * * root /root/reminders/tasks/hourly >> /root/reminders/logs/$DATEVAR

There's a few issues with this though.

1. I receive the email, but it only contains any errors that the script might output. (stderr)
2. A log file is created, containing the output of the script, minus the errors that I received in the email (stdout)
3. The name of the log file is not the date/time. It's the literal value of the variable (date -d '+1 hour' +'\%d_\%m_\%Y_\%H')

I am using Debian 11.5 and I was under the impression that vixie-cron was able to handle variables.

What I'm I doing wrong here?

elgrandeperro · 10-29-2022, 11:52 PM

First, you aren't executing date. You need backticks to execute and set the DATEVAR. I think if you substitute backtick instead of double quote it will work.

Second, to map stderr to stdout, put 2>&1
http://www.linuxask.com/questions/me...-21-in-crontab

Most people don't want to get those annoying emails on success, but you can figure out what you want later.

Lastlty, you redirect stdout to the file, so you don't get output via the cron mail. Use tee if you want output both to the file
and in the email. Tee replicates stdout to both places.

aristosv · 10-30-2022, 12:08 AM

I think this is everything you mentioned

Code:

MAILTO=me@myemail.com
DATEVAR=`date -d '+1 hour' +'\%d_\%m_\%Y_\%H'`
0 * * * * root /root/reminders/tasks/hourly 2>&1 | tee /root/reminders/logs/$DATEVAR

I'll know in a hour when the job runs again.

aristosv · 10-30-2022, 02:15 AM

I got an email saying

tee: invalid option -- 'd'
Try 'tee --help' for more information.

and the log file still kept the name "date -d '+1 hour' +'\%d_\%m_\%Y_\%H'"

scasey · 10-30-2022, 03:09 AM

I’m going to guess that the path to date and/or tee is not known to the cron environment. Use absolute paths to all commands used. Use which to discover what the path is…e.g.:

Code:

which date

I’m also guessing that, since your command didn’t run, you’re looking at a old instance of the file. Use

Code:

ls -l

to see the date time on the file, and/or remove or rename the erroneous file(s) created before your test.

Also, you don’t need to wait an hour between tests. Just set the second column to (say) 5 minutes from “now” Change it back when everything else is working as you want.

michaelk · 10-30-2022, 07:55 AM

Since a cron job is not associated to a terminal window the tee command will not work as expected.

Are you using root's crontab (i.e crontab -e ) or a system cron job i.e /etc/crontab? If you are using root's crontab then a username is not required.

Code:

0 * * * * /root/reminders/tasks/hourly 2>&1 | tee /root/reminders/logs/$(date -d "+1 hour" +'\%d_\%m_\%Y_\%H')

MadeInGermany · 10-30-2022, 08:07 AM

Use $( ) instead of ` `
cron requires a % backslash-escaped, so ensure there is no further quoting (or the shell will do literal backslashes)

Code:

MAILTO=me@myemail.com
DATEVAR=$( date -d '+1 hour' +\%d_\%m_\%Y_\%H )
0 * * * * root /root/reminders/tasks/hourly >> /root/reminders/logs/$DATEVAR

computersavvy · 10-30-2022, 08:28 PM

With my version of the date command the \ is an issue.
with the backslash I get

Code:

$ date -d '+1 hour' +'\%d_\%m_\%Y_\%H'
\30_\10_\2022_\21

and without it I get

Code:

$ date -d '+1 hour' +'%d_%m_%Y_%H'
30_10_2022_21

So I would suggest you try

Code:

MAILTO=me@myemail.com

0 * * * * root DATEVAR=$( date -d '+1 hour' +%d_%m_%Y_%H ) ; /root/reminders/tasks/hourly 2>&1 >> /root/reminders/logs/$DATEVAR

As noted your script may be correct if it is in /etc/crontab, but if it is in root's personal crontab then it should read as

Code:

MAILTO=me@myemail.com

0 * * * * DATEVAR=$( date -d '+1 hour' +%d_%m_%Y_%H ) ; /root/reminders/tasks/hourly 2>&1 >> /root/reminders/logs/$DATEVAR

In either case if you want an email when there is an error then remove the '2>&1' from that line. The output would not normally be emailed to you unless you added something like '&& echo "/root/reminders/logs/$DATEVAR completed"' to the end of that command line so it sends you a simple completion message each time it successfully runs.

If the crontab line read something like this you would get one message with an error and a different message when successful

Code:

0 * * * * DATEVAR=$( date -d '+1 hour' +%d_%m_%Y_%H ) ; /root/reminders/tasks/hourly > /root/reminders/logs/$DATEVAR && echo "/root/reminders/logs/$DATEVAR completed"

michaelk · 10-30-2022, 09:18 PM

From the crontab man pages

Quote:

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 a "%" character, will be executed by /bin/sh or by the shell
specified in the SHELL variable of the cronfile. A "%" character
in the command, unless escaped with a backslash (\), will be
changed into newline characters, and all data after the first %
will be sent to the command as standard input.

rnturn · 10-30-2022, 09:33 PM

Quote:

Originally Posted by aristosv

I have a cronjob running a script every hour. I want it to email me the output, and also write the output to a log file. Both stdout & stderr.

Code:

MAILTO="me@myemail.com"
DATEVAR="date -d '+1 hour' +'\%d_\%m_\%Y_\%H'"
0 * * * * root /root/reminders/tasks/hourly >> /root/reminders/logs/$DATEVAR

Simplify, simplify.

Write a script that creates the disk file (with whatever date-related filename you want to use) containing the data you want to email, then email the file from within the script. There's a copy of the output on disk and another sent to the user---which seems to be what you want. Then, have cron run that script.

cron is meant to execute commands/scripts. It's not really intended to be a programming environment.

HTH...