Log crontab shell script errors with error occurred time?

Question

A common way to log crontab errors looks like below:

1 */8 * * * sh /pseudo_path/test.sh 2>> my_err_log 

It's a concise command, but it can't record the error occurred time, and the path of script file is omitted.

So I wrote an error record function:

PROGNAME=$(readlink -f "$0")
SCRIPT_ERR_LOG_PATH="/pseudo_path/script_err_log"

error_exit()
{
    timestamp="$(date +%Y%m%d-%H:%M:%S)"
    x_info=$(echo "Error_${PROGNAME}:Line_${1:-"null"}_")
    zeta=$x_info$timestamp
    echo "$zeta" >> $SCRIPT_ERR_LOG_PATH
    exit 1
}

This function can log the time the error occurred, together with the absolute path of the script. But the downside is that I have to add || error_exit $LINENO at every line of my script to make it work. With Vim's bulk substitution it could be much easier, but it still looks like a clumsy solution.

So, is there a smarter or more efficient way to do the same task?

Answer 1

It looks to me like you're creating a Bash script, so take advantage of Bash's trap builtin. For example:

#!/bin/bash
# vim: ft=sh:tw=75:fo-=t:fo+=rcq:ai:

function error_trap()
{
    local -ir __exit_code__=${1:-$?}
    local __timestamp__

    # Reset the ERR sigspec to its original disposition.
    trap - ERR

    __timestamp__=$( date --rfc-3339=seconds --date=now )

    # Hint...
    #declare -p BASH_LINENO
    #declare -p BASH_COMMAND

    echo "[${__timestamp__}] (Line: ${BASH_LINENO[0]}) :: ERROR :: ${BASH_COMMAND}" >&2

    exit ${__exit_code__}
}

# Register function 'error_trap' as the trap handler for
# the ERR (error) sigspec.
trap "{ error_trap; }" ERR

# Try it out; deliberately crash-and-burn this script.
ls this-does-not-exist

Here's the output I see when I invoke this script:

ls: cannot access this-does-not-exist: No such file or directory
[2015-07-30 01:36:32-05:00] (Line: 24) :: ERROR :: ls this-does-not-exist

Answer 2

Depending on the quantity of the logging information you're expecting to produce, it might be worth using the standard logger tool to write it to the user syslog in /var/log:

1 */8 * * * /path/to/myprog 2>&1 | logger -p user.debug -t 'myprog'

Here is an example of the output written to /var/log/debug on my Debian-based system:

Jul 31 00:17:09 myserver myprog: test message with user.debug

There are various facility/level pairs available for use. You might want to consider user.notice or user.info or user.debug. Just be aware that some of these may also get written to /var/log/messages and /var/log/syslog.

---

If you want to differentiate stdout and stderr in your cron job, sending only stderr to the logger, you can use a construct like this, which I'm sure others will improve upon:

1 */8 * * * ( /path/to/myprog 2>&1 1>&3 | logger -p user.debug -t 'myprog' ) 3>&1