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

   1 #!/bin/bash
   2 # I, Ian Kelling, follow the GNU license recommendations at
   3 # https://www.gnu.org/licenses/license-recommendations.en.html. They
   4 # recommend that small programs, < 300 lines, be licensed under the
   5 # Apache License 2.0. This file contains or is part of one or more small
   6 # programs. If a small program grows beyond 300 lines, I plan to switch
   7 # its license to GPL.
   8
   9 # Copyright 2024 Ian Kelling
  10
  11 # Licensed under the Apache License, Version 2.0 (the "License");
  12 # you may not use this file except in compliance with the License.
  13 # You may obtain a copy of the License at
  14
  15 #     http://www.apache.org/licenses/LICENSE-2.0
  16
  17 # Unless required by applicable law or agreed to in writing, software
  18 # distributed under the License is distributed on an "AS IS" BASIS,
  19 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  20 # See the License for the specific language governing permissions and
  21 # limitations under the License.
  22
  23 # Copyright (C) 2019 Ian Kelling
  24 # Log errors once or so instead of many times.
  25
  26     # This program is free software: you can redistribute it and/or modify
  27     # it under the terms of the GNU General Public License as published by
  28     # the Free Software Foundation, either version 3 of the License, or
  29     # (at your option) any later version.
  30
  31     # This program is distributed in the hope that it will be useful,
  32     # but WITHOUT ANY WARRANTY; without even the implied warranty of
  33     # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  34     # GNU General Public License for more details.
  35
  36     # You should have received a copy of the GNU General Public License
  37     # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  38
  39 # SPDX-License-Identifier: GPL-3.0-or-later
  40
  41 append() {
  42   cat >> "$1"
  43 }
  44 log-once() {
  45   local cbase c log line i out file o tmp mvout mverr verbose
  46   cbase=/var/local/cron-errors
  47   [[ $EUID == 0 ]] || cbase=$HOME/cron-errors
  48   local help="Usage: some-command-that-outputs-on-error |& log-once [OPTION]... LOG_NAME
  49
  50 Main use case: in cronjobs where STDIN represents an error,
  51 but we only want to output that to STDOUT if we've seen this type of
  52 error ERRORS(default 3) number of times in a row, then we don't
  53 want to output anything again until we've seen a success: no standard input.
  54
  55 Logs STDIN to /var/local/cron-errors/LOG_NAME\$error_count or
  56 $HOME/cron-errors if not root, and keeps state in the same directory.
  57
  58 -ERRORS:  ERRORS is the number of errors to accumulate before outputing the error
  59 -v:       Output the errors along the way to ERRORS
  60
  61
  62 You can emulate how cronjobs work by doing this for example:
  63
  64     cmdname |& log-once | ifne mail -s 'cmdname failed' root@localhost
  65
  66 I could imagine a similar command that considers its non-option args to
  67 be an error, but I haven't written it yet.
  68 "
  69   errors=3
  70   mverr=0
  71   verbose=false
  72
  73   while true; do
  74     if [[ $1 == --help ]]; then
  75       echo "$help"
  76       return
  77     elif [[ $1 == -v ]]; then
  78       verbose=true
  79       shift
  80     elif [[ $1 == -[0-9]* ]]; then
  81       errors=${1#-}
  82       shift
  83     elif [[ $1 == -- ]]; then
  84       shift
  85       break
  86     else
  87       break
  88     fi
  89   done
  90   log_name=$1
  91   # todo, make option & make them overridable based on command line or env variable
  92   [[ -d $cbase ]] || mkdir -p $cbase
  93   c=$cbase/$log_name
  94   log=false
  95   while read -r line; do
  96     output+=( "$line" )
  97     # If we find something that is not just a newline:
  98     if [[ $line ]]; then
  99       log=true
 100       break
 101     fi
 102   done
 103   glob="$c[0-9]*"
 104   # file is error file indicating previous error
 105   tmp=($glob); file="${tmp[0]}"
 106   if [[ $file == "$glob" ]]; then
 107     file=
 108   fi
 109   if $log; then
 110     out=append
 111     if [[ $file ]]; then
 112       i="${file#$c}"
 113       if (( i < errors )); then
 114         new_file=$c$((i+1))
 115         mvout=$(mv $file $new_file 2>&1) || mverr=$?
 116         if (( mverr )); then
 117           if [[ $mvout == *": No such file or directory" ]]; then
 118             # We've very likely hit a race condition, where another
 119             # log-once did the mv before us.
 120             return 0
 121           else
 122             echo "log-once: error on mv $file $new_file"
 123             return $mverr
 124           fi
 125         fi
 126         file=$new_file
 127         if [[ $file == $c$errors ]] || $verbose; then
 128           out="tee -a"
 129         fi
 130       fi
 131     else
 132       file=${c}1
 133       if (( errors == 1 )); then
 134         out="tee -a"
 135       fi
 136     fi
 137     $out $file <<<"log-once: $(date -R)"
 138     if [[ $2 ]]; then
 139       $out $file <<<"$*"
 140     else
 141       for o in "${output[@]}"; do
 142         $out $file <<<"$o"
 143       done
 144       $out $file
 145     fi
 146     return 0
 147   fi
 148   if [[ $file ]]; then
 149     rm -f $file
 150     if [[ $file == $c$errors ]]; then
 151       echo "log-once: $(date -R): success after failure for $c"
 152     fi
 153   fi
 154   return 0
 155 }
 156 log-once "$@"