iankelling.org Git - log-quiet/blob - log-once

   1 #!/bin/bash
   2 # Copyright (C) 2019 Ian Kelling
   3 # Log errors once or so instead of many times.
   4
   5     # This program is free software: you can redistribute it and/or modify
   6     # it under the terms of the GNU General Public License as published by
   7     # the Free Software Foundation, either version 3 of the License, or
   8     # (at your option) any later version.
   9
  10     # This program is distributed in the hope that it will be useful,
  11     # but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     # GNU General Public License for more details.
  14
  15     # You should have received a copy of the GNU General Public License
  16     # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17
  18 # SPDX-License-Identifier: GPL-3.0-or-later
  19
  20 append() {
  21   cat >> "$1"
  22 }
  23 log-once() {
  24   local cbase c log line i out file o tmp mvout mverr verbose
  25   cbase=/var/local/cron-errors
  26   [[ $EUID == 0 ]] || cbase=$HOME/cron-errors
  27   local help="Usage: some-command-that-outputs-on-error |& log-once [OPTION]... LOG_NAME
  28
  29 Main use case: in cronjobs where STDIN represents an error,
  30 but we only want to output that to STDOUT if we've seen this type of
  31 error ERRORS(default 3) number of times in a row, then we don't
  32 want to output anything again until we've seen a success: no standard input.
  33
  34 Logs STDIN to /var/local/cron-errors/LOG_NAME\$error_count or
  35 $HOME/cron-errors if not root, and keeps state in the same directory.
  36
  37 -ERRORS:  ERRORS is the number of errors to accumulate before outputing the error
  38 -v:       Output the errors along the way to ERRORS
  39
  40
  41 You can emulate how cronjobs work by doing this for example:
  42
  43     cmdname |& log-once | ifne mail -s 'cmdname failed' root@localhost
  44
  45 I could imagine a similar command that considers its non-option args to
  46 be an error, but I haven't written it yet.
  47 "
  48   errors=3
  49   mverr=0
  50   verbose=false
  51
  52   while true; do
  53     if [[ $1 == --help ]]; then
  54       echo "$help"
  55       return
  56     elif [[ $1 == -v ]]; then
  57       verbose=true
  58       shift
  59     elif [[ $1 == -[0-9]* ]]; then
  60       errors=${1#-}
  61       shift
  62     elif [[ $1 == -- ]]; then
  63       shift
  64       break
  65     else
  66       break
  67     fi
  68   done
  69   log_name=$1
  70   # todo, make option & make them overridable based on command line or env variable
  71   [[ -d $cbase ]] || mkdir -p $cbase
  72   c=$cbase/$log_name
  73   log=false
  74   while read -r line; do
  75     output+=( "$line" )
  76     # If we find something that is not just a newline:
  77     if [[ $line ]]; then
  78       log=true
  79       break
  80     fi
  81   done
  82   glob="$c[0-9]*"
  83   # file is error file indicating previous error
  84   tmp=($glob); file="${tmp[0]}"
  85   if [[ $file == "$glob" ]]; then
  86     file=
  87   fi
  88   if $log; then
  89     out=append
  90     if [[ $file ]]; then
  91       i="${file#$c}"
  92       if (( i < errors )); then
  93         new_file=$c$((i+1))
  94         mvout=$(mv $file $new_file 2>&1) || mverr=$?
  95         if (( mverr )); then
  96           if [[ $mvout == *": No such file or directory" ]]; then
  97             # We've very likely hit a race condition, where another
  98             # log-once did the mv before us.
  99             return 0
 100           else
 101             echo "log-once: error on mv $file $new_file"
 102             return $mverr
 103           fi
 104         fi
 105         file=$new_file
 106         if [[ $file == $c$errors ]] || $verbose; then
 107           out="tee -a"
 108         fi
 109       fi
 110     else
 111       file=${c}1
 112       if (( errors == 1 )); then
 113         out="tee -a"
 114       fi
 115     fi
 116     $out $file <<<"log-once: $(date -R)"
 117     if [[ $2 ]]; then
 118       $out $file <<<"$*"
 119     else
 120       for o in "${output[@]}"; do
 121         $out $file <<<"$o"
 122       done
 123       $out $file
 124     fi
 125     return 0
 126   fi
 127   if [[ $file ]]; then
 128     rm -f $file
 129     if [[ $file == $c$errors ]]; then
 130       echo "log-once: $(date -R): success after failure for $c"
 131     fi
 132   fi
 133   return 0
 134 }
 135 log-once "$@"