Have cron email output to MAILTO based on exit status

Question

I have a cron job running a php command like this:

php /path/to/script.php > dev/null

This should send only STDERR output to the MAILTO address. From what I gather the php script is not outputting any STDERR information even when its exit status is 1.

How can I get the output of the php command (STDOUT) and only send it to MAILTO if the exit status is non-zero?

Answer 1

php /path/to/script.php > logfile || cat logfile; rm logfile

which dumps standard output into logfile and only outputs it if the script fails (exits non-zero).

Answer 2

Since the output is generated before the exit status is known, you'll have to store it somewhere.

One possibility is to store it in a shell variable:

output=$(php /path/to/script.php)
if [ $? -ne 0 ]; then
  printf "%s\n" "$output"
fi

This doesn't completely preserve the script's output (it removes trailing blank lines), but that's ok for this use case. If you want to preserve trailing blank lines:

output=$(php /path/to/script.php; ret=$?; echo a; exit $ret)
if [ $? -ne 0 ]; then
  printf "%s" "${output%a}"
fi

If there's potentially a lot of output, you might prefer to store it in a temporary file instead:

output_file=$(mktemp /var/tmp/script.XXXXXXXXXX.out)
php /path/to/script.php >>"$output_file"
ret=$?
if [ $ret -ne 0 ]; then
  echo "script.php failed (status $ret), see the output in $output_file"
fi

Answer 3

Someone wrote a script called cronlog. It runs a command, and prints the whole output (both STDOUT and STDERR) of the command to the standard output only if the exit status is non-zero; it prints nothing at all if zero.

Put this script to your $PATH, and you can write the cronjob like this:

cronlog -- php /path/to/script.php

You can also prepend the timestamp to each line of the output and/or log the output of every run (including succeeded ones) to a file:

cronlog --timestamp --logfile=$HOME/cron.log -- php /path/to/script.php