handle properties file with bash using awk and sort

set-properties

#!/bin/bash
#/ Define properties and sort them in a file
#/ Usage: 
#/    set_property key value filename
#/ Alternative:
#/
#/ export PROPERTIES_FILE=myproperties
#/    set_property key value
#/ --------------------------------------------------------------------------------
#/ Author: Rogério Peixoto (rcbpeixoto@gmail.com)
#/ --------------------------------------------------------------------------------
usage() { grep '^#/' "$0" | cut -c4- ; exit 0 ; }
expr "$*" : ".*--help" > /dev/null && usage

set_property(){
  if [ -z "$1" ]; then
    echo "No parameters provided, exiting..."
    exit 1
  fi
  if [ -z "$2" ]; then
    echo "Key provided, but no value, breaking"
    exit 1
  fi
  if [ -z "$3" ] && [ -z "$PROPERTIES_FILE" ]; then
    echo "No file provided or PROPERTIES_FILE is not set, exiting..."
    exit 1
  fi

  if [ "$PROPERTIES_FILE" ] && [ "$3" ]; then
      echo "PROPERTIES_FILE variable is set AND filename in comamnd! Use only or the other. Exiting..."
      exit 1
  else
    if [ "$3" ] && [ ! -f "$3" ]; then
      echo "File in command NOT FOUND!"
      exit 1
    elif [ "$PROPERTIES_FILE" ] && [ ! -f "$PROPERTIES_FILE" ]; then
      echo "File in PROPERTIES_FILE variable NOT FOUND!"
      exit 1
    fi
  fi

  if [ "$PROPERTIES_FILE" ]; then
    file=$PROPERTIES_FILE
  else
    file=$3
  fi

  tempfile=$(mktemp "/tmp/$file.XXXXXX")

  existing=$(cat $file | grep $1=)

  if [ -z $existing ]; then
    cat $file >> $tempfile
    echo "$1=$2" >> $tempfile
  else 
    awk -v pat="^$1=" -v value="$1=$2" '{ if ($0 ~ pat) print value; else print $0; }' "$file" > "$tempfile"
  fi

  sort_tempfile=$(mktemp "/tmp/$file.XXXXXX")

  cat $tempfile | sort > "$sort_tempfile"
  tempfile=$sort_tempfile

  mv "$tempfile" "$file"
}