Parses a Heroku log (defaults to /var/log/heroku, but you can pass it a log file as the first argument to the script), then prints out the date and hour, the error code, the count, and the percentage of the total.

errors-by-date-hour

#!/bin/bash

# ---------------
# Example output:
# ---------------
#    Date/Hour      Error      Count  % of Total
#     3-Oct 03   code=H12         98      73.68%
#     3-Oct 04   code=H12         35      26.32%

LOG=${1:-/var/log/heroku}

awk 'BEGIN{ printf "%12s %10s %10s %11s\n", "Date/Hour", "Error", "Count", "% of Total" }'

egrep 'code=(H|R)' $LOG | awk '{
  split($3,time,":")
  dayHour=$2"-"$1" "time[1]
  a[dayHour]++;total++
}
END {
  for(i in a){
    printf "%12s %10s %10s %10.2f%%\n", i, $8, a[i], a[i]/total*100;
  }
}' | sort