trunclog.sh

function trunclog {
  # Truncate a log file and leave N lines of tail remaining.
  if [ "$*" = "" ]
  then
    echo "Usage: trunclog [lines] [log-file]"
  else
    REQUESTED_LINES=$1
    LOG=$2
    TEMP=/tmp/`basename $LOG`.tmp.$$
    tail -$REQUESTED_LINES $LOG > $TEMP
    ACTUAL_LINES=`wc -l $TEMP | awk '{print $1'}`
    if [[ $ACTUAL_LINES == $REQUESTED_LINES || $((ACTUAL_LINES+1)) == $REQUESTED_LINES ]]
    then
      rm $LOG
      mv -f $TEMP $LOG
      echo "Truncated $LOG to $REQUESTED_LINES lines"
    else
      echo "Found fewer lines. Check actual lines with "wc -l $LOG" and check disk space on /tmp with "df /tmp"."
    fi
  fi
}