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

   1 #!/bin/bash
   2 # Copyright (C) 2019 Ian Kelling
   3 # SPDX-License-Identifier: AGPL-3.0-or-later
   4
   5 append() {
   6   cat >> "$1"
   7 }
   8 log-once() {
   9   local cbase c log line i out file o tmp mvout mverr
  10   cbase=/var/local/cron-errors
  11   [[ $EUID == 0 ]] || cbase=$HOME/cron-errors
  12   local help="Usage: some-command-that-outputs-on-error |& log-once [OPTION]... LOG_NAME
  13
  14 Main use case: in cronjobs where STDIN represents an error,
  15 but we only want to output that to STDOUT if we've seen this type of
  16 error ERRORS(default 3) number of times in a row, then we don't
  17 want to output anything again until we've seen a success: no standard input.
  18
  19 Logs STDIN to /var/local/cron-errors/LOG_NAME\$error_count or
  20 $HOME/cron-errors if not root, and keeps state in the same directory.
  21
  22 -ERRORS:  ERRORS is the number of errors to accumulate before outputing the error
  23
  24
  25 You can emulate how cronjobs work by doing this for example:
  26
  27     cmdname |& log-once | ifne mail -s 'cmdname failed' root@localhost
  28
  29 I could imagine a similar command that considers its non-option args to
  30 be an error, but I haven't written it yet.
  31 "
  32   errors=3
  33   mverr=0
  34   while true; do
  35     if [[ $1 == --help ]]; then
  36       echo "$help"
  37       return
  38     elif [[ $1 == -[0-9]* ]]; then
  39       errors=${1#-}
  40       shift
  41     elif [[ $1 == -- ]]; then
  42       shift
  43       break
  44     else
  45       break
  46     fi
  47   done
  48   log_name=$1
  49   # todo, make option & make them overridable based on command line or env variable
  50   [[ -d $cbase ]] || mkdir -p $cbase
  51   c=$cbase/$log_name
  52   log=false
  53   while read -r line; do
  54     output+=( "$line" )
  55     # If we find something that is not just a newline:
  56     if [[ $line ]]; then
  57       log=true
  58       break
  59     fi
  60   done
  61   glob="$c[0-9]*"
  62   # file is error file indicating previous error
  63   tmp=($glob); file="${tmp[0]}"
  64   if [[ $file == "$glob" ]]; then
  65     file=
  66   fi
  67   if $log; then
  68     out=append
  69     if [[ $file ]]; then
  70       i="${file#$c}"
  71       if (( i < errors )); then
  72         new_file=$c$((i+1))
  73         mvout=$(mv $file $new_file 2>&1) || mverr=$?
  74         if (( mverr )); then
  75           if [[ $mvout == *": No such file or directory" ]]; then
  76             # We've very likely hit a race condition, where another
  77             # log-once did the mv before us.
  78             return 0
  79           else
  80             echo "log-once: error on mv $file $new_file"
  81             return $mverr
  82           fi
  83         fi
  84         file=$new_file
  85         if [[ $file == $c$errors ]]; then
  86           out="tee -a"
  87         fi
  88       fi
  89     else
  90       file=${c}1
  91       if (( errors == 1 )); then
  92         out="tee -a"
  93       fi
  94     fi
  95     $out $file <<<"log-once: $(date -R)"
  96     if [[ $2 ]]; then
  97       $out $file <<<"$*"
  98     else
  99       for o in "${output[@]}"; do
 100         $out $file <<<"$o"
 101       done
 102       $out $file
 103     fi
 104     return 0
 105   fi
 106   if [[ $file ]]; then
 107     rm -f $file
 108     if [[ $file == $c$errors ]]; then
 109       echo "log-once: $(date -R): success after failure for $c"
 110     fi
 111   fi
 112   return 0
 113 }
 114 log-once "$@"