nagios script to check log files

check_logfile

#!/usr/bin/env bash

PROGRAM="$(/bin/basename "$0")"
REVISION="1.0.0"

STATE_OK=0
STATE_CRITICAL=2
STATE_UNKNOWN=3

revision_details() {
  echo "$1 v$2 (nagios-plugins 2.0.3)"
  echo "The nagios plugins come with ABSOLUTELY NO WARRANTY. You may redistribute"
  echo "copies of the plugins under the terms of the GNU General Public License."
  echo "For more information about these matters, see the file named COPYING."
  echo
  return 0
}

usage() {
    cat <<EOF
Usage:
    ${PROGRAM} [options] <regexp>[ <regexp>[ <regexp[ ...]]]

Options:
    -f, --file <FILE>      Logfile to search
    -x, --exitcode <CODE>  Code to exit with if match successful
    -i, --invert           Invert match expression (found == fail, not found = success)
    -s, --start-at <LINE>  Line number to start looking from
    -v, --verbose          Verbose output
    -V, --version          Show version and exit
    -h, --help             Show usage information and exit

EOF
    return 0
}

show_help() {
    revision_details "${PROGRAM}" "${REVISION}"
    usage
    echo -e "Log file pattern detector plugin for Nagios\n"
    return 0
}

option_fail() {
  [ $# -gt 0 ] && echo -e "Error: $*\n"
  show_help
  exit $STATE_UNKNOWN
}

exitcode=$STATE_OK #default
verbose=0
invert=0

[ $# -lt 1 ] && show_help && exit $STATE_UNKNOWN

OPTS=$(getopt --name "${PROGRAM}" -o f:x:s:ivhV -l file:,exitcode:,start-at:invert,verbose,help,version -- "$@")
[ $? != 0 ] && exit 1
eval set -- "${OPTS}"

while true; do
  case "$1" in
    --help|-h) show_help; exit $STATE_OK ;;
    --version|-V) revision_details "${PROGRAM}" "${REVISION}"; exit $STATE_OK ;;
    --verbose|-v) verbose=$((verbose + 1));;
    --invert|-i) invert=1;;
    --start-at|-s) start_at=$2; shift 1;;
    --file|-f) 
      logfile="$2"; 
      idxfile="/var/tmp/$(echo "${logfile}" | md5sum | awk '{ print $1 }').idx"
      shift 1;;
    --exitcode|-x) 
      found_exitcode=$(($2 + 0)) # this silences certain errors on shellcheck.net
      shift 1;;
    --) shift; break;;
    *) echo "Unknown argument: $1" && usage && exit $STATE_UNKNOWN;;
  esac
  shift
done

[ ${verbose} -gt 0 ] && set -x
[ ${verbose} -gt 1 ] && set -v

[ -n "${logfile}" ] || option_fail "logfile not specified!"
[ -r "${logfile}" ] || option_fail "logfile not readable"
[ $# -ne 0 ] || option_fail "no regular expressions specified!"

if [ ! -e "${idxfile}" ]; then
  echo -en 0 > "${idxfile}"
fi

idx_line=$(cat "${idxfile}")
start_at=$((${start_at:-${idx_line}} + 0))
current_line_count=$(wc -l < "${logfile}")

# if the number of lines in the file is less than the current
# start_at marker, reset start_at to 0
[[ ${current_line_count} -lt ${start_at} ]] && start_at=0

# update the stored line index
echo -en "${current_line_count}" > "${idxfile}"

# determine total number of lines to check
check_line_count=$((current_line_count - start_at - 1))
[[ ${check_line_count} -lt 0 ]] && check_line_count=0

output=()
line_matches=0
regexp_matches=0

for regexp in "$@"; do
  found=$(tail -n+${start_at} "${logfile}" | head -n${check_line_count} | grep -Pc "${regexp}")
  line_matches=$((line_matches + found))
  if [[ ${found} -gt 0 ]]; then
    regexp_matches=$((regexp_matches + 1))
    output+=( "${found} matches for expression '${regexp}'" )
    [[ ${invert} -eq 0 ]] && exitcode=${found_exitcode:-$STATE_CRITICAL}
  else
    output+=( "no matches found for expression '${regexp}'" )
    # with inversion, any expression /not/ found causes termination
    # with exit code == ( user defined exitcode || state_critical )
    [[ ${invert} -eq 1 ]] && exitcode=${found_exitcode:-$STATE_CRITICAL}
  fi
done

echo "${line_matches} matches found from ${regexp_matches} expression(s)"
for msg in "${output[@]}"; do
  echo "  - $msg"
done
exit $exitcode