Initial commit

binary_backups.sh

@@ -0,0 +1,110 @@
+#!/bin/bash
+
+# These knobs control which backups to keep, and how long to keep them for. A
+# backup is kept if its distance from the UNIX epoch in days divides evenly by
+# BASE^power (where power is some integer 0 < MAX_POWER), and it is less than
+# WINDOW_FACTOR*BASE^power days old.
+BASE=2
+MAX_POWER=16
+WINDOW_FACTOR=4
+
+# Returns output if the date passed in as the first argument is not in a format
+# 'date' can understand
+function invalid_date() {
+  date -d "$1 + 1 min" +"%s" &> /dev/null
+  if [[ $? -ne 0 ]]; then
+    echo "invalid"
+  fi
+}
+
+# Return the number of days which passed between the UNIX epoch and the first
+# argument
+function days_since_epoch() {
+  echo $(( $(date -d "$1" +"%s") / (60*60*24) ))
+}
+
+# Prints "keep" if the backup with the indicated date should be kept
+function keep_backup() {
+  local current_day_count=$1
+  local backup_day_count=$2
+  local difference=$(( $current_day_count - $backup_day_count ))
+
+  for (( power=0; power<=$MAX_POWER; power++ )); do
+    local factor=$(( $BASE ** $power ))
+    local remainder=$(( $backup_day_count % $factor ))
+    if [[ $remainder -eq 0 ]] &&
+        [[ $difference -le $(($factor * $WINDOW_FACTOR)) ]]; then
+      echo "keep"
+      return
+    fi
+  done
+}
+
+function usage() {
+cat << EOF
+Usage: $0 options
+
+Print the backups which should (or should not with -r) be kept from a list of
+dates passed via stdin.
+
+OPTIONS:
+   -h       Show this message
+   -i FILE  Read candidate backup dates from FILE instead of stdin
+   -d DATE  Calculate which backups should be kept from this date instead of
+            today 
+   -r       Reverse which dates are displayed (show those which should be
+            deleted instead of kept)
+EOF
+}
+
+reverse=
+current_date=$(date -I)
+input="/dev/stdin"
+
+while getopts "hrd:i:" OPTION; do
+  case $OPTION in
+    i)
+      input=$OPTARG
+      if [[ ! -f $input ]]; then
+        echo "Error: \"$input\" is not a file"
+        usage
+        exit 1
+      fi
+      ;;
+    d)
+      current_date=$OPTARG
+      if [[ $(invalid_date "$current_date") ]]; then
+        echo "Error: \"$current_date\" is not a valid date"
+        usage
+        exit 1
+      fi
+      ;;
+    r)
+      reverse="true"
+      ;;
+    h)
+      usage
+      exit
+      ;;
+    ?)
+      usage
+      exit 1
+      ;;
+  esac
+done
+
+current_days=$(days_since_epoch "$current_date")
+
+while read line; do
+  if [[ $(invalid_date "$line") ]]; then
+    echo "Error: \"$line\" is not a valid date"
+    exit 1
+  fi
+  backup_days=$(days_since_epoch "$line")
+  keep=$(keep_backup $current_days $backup_days)
+  if [[ -z $reverse ]] && [[ $keep ]]; then
+    echo $line
+  elif [[ $reverse ]] && [[ -z $keep ]]; then
+    echo $line
+  fi
+done < $input