An enhanced version of [cronic - a cure for cron's chronic email problem](http://habilis.net/cronic/) that supports logging task output to a file for situations where you want to keep history on the server for further inspection but only want to be emailed if your task fails.

cronic

#!/bin/bash

# Cronic v2 - cron job report wrapper
# Copyright 2007 Chuck Houpt. No rights reserved, whatsoever.
# Amended 2013 Andrew Coulton.
# Public Domain CC0: http://creativecommons.org/publicdomain/zero/1.0/

# Basic usage, to run a task and discard the output unless it fails or outputs to STDERR
# cronic /run/my/task 
# 
# Enhanced usage, to run a task, always log to a file and only output for email if it fails or outputs to STDERR
# CRONIC_REPORT=/var/log/mytask/mytask cronic /run/my/task
#
# Each execution will log output to files called something like /var/log/mytask/mytask-{unix-timestamp}.out, 
# .err and .trace. Presuming cronic itself survives these will be combined post-run to a single .log file.
# If the task outputs anything to STDERR or quits with a nonzero exit code this output will be sent to 
# the console (and if running under cron will become the email body).
# The directory must exist

set -eu

TASKID=$(date +%s)
CRONIC_REPORT="${CRONIC_REPORT:=}"

# Prepare paths for working and report files
if [ -z "$CRONIC_REPORT" ]
  then
  OUT=/tmp/cronic.out.$$
  ERR=/tmp/cronic.err.$$
  TRACE=/tmp/cronic.trace.$$
  REPORT=/tmp/cronic.report.$$
else
  OUT="$CRONIC_REPORT-$TASKID.out"
  ERR="$CRONIC_REPORT-$TASKID.err"
  TRACE="$CRONIC_REPORT-$TASKID.trace"
  REPORT="$CRONIC_REPORT-$TASKID.log"
fi

# Run the subcommand
set +e
"$@" >$OUT 2>$TRACE
RESULT=$?
set -e

# Filter any trace output
PATTERN="^${PS4:0:1}\\+${PS4:1}"
if grep -aq "$PATTERN" $TRACE
then
    ! grep -av "$PATTERN" $TRACE > $ERR
else
    ERR=$TRACE
fi

# Build the report log file ready for output
if [ $RESULT -ne 0 -o -s "$ERR" ]
then
	echo "Cronic detected failure or error output for the command:" > $REPORT
else
	echo "Cronic detected successful execution of the command:" > $REPORT
fi
echo "$@" >> $REPORT
echo ""   >> $REPORT
echo "RESULT CODE: $RESULT" >> $REPORT
echo "" >> $REPORT
echo "ERROR OUTPUT:" >> $REPORT
cat "$ERR" >> $REPORT
echo "" >> $REPORT
echo "STANDARD OUTPUT:" >> $REPORT
cat "$OUT" >> $REPORT
if [ $TRACE != $ERR ]
then
	echo "" >> $REPORT
    echo "TRACE-ERROR OUTPUT:" >> $REPORT
	cat "$TRACE" >> $REPORT
fi

# If there was an error, output the report to trigger an email
if [ $RESULT -ne 0 -o -s "$ERR" ]
then
	cat "$REPORT"
fi

# Remove the temporary working files
rm -f "$OUT"
rm -f "$ERR"
rm -f "$TRACE"

# Remove the report file if not configured to keep it
if [ -z "$CRONIC_REPORT" ]
then
	rm -f "$REPORT"
fi