Expand properties in bash

properties-expander.sh

#!/bin/bash
#
# Released under the WTFPL license version 2 http://sam.zoy.org/wtfpl/
# Copyright (c) 2012 Emmanuel Bernard
# -----
# Usage: properties-expander.sh <properties file> <template> <destination>
#
# Properties file:
#   PROPERTY1=value1
#   PROPERTY2=value2

#help
if [[ $# -ne 3 ]]; then 
  echo "properties-expander.sh <properties file> <template> <destination>"
  exit 0;
fi

echo Expanding $2 to $3 with properties from $1

#read each line including the last one
while IFS=$'\n' read -r line || [[ -n "$line" ]]; do
	#get the property name before the first =
    property=${line%%=*}
    #get the value after the first =
    value=${line#*=}

    #find a suitable separation character as the value might contain /
    candidates='/:.|@#%^&;,!~abcABC'  # candidates for separation character
    char=$(echo "$candidates" | tr -d "$line")  
    char=${char:0:1}   # choose the first candidate that doesn't appear in the user input

    if [ -z "$char" ]    # this test checks for exhaustion of the candidate character set
    then
        echo "Unusable user input: $line"
        exit 1
    fi

    #add regexp rule
    SEDEXEC="s${char}\$$property${char}$value${char}g;$SEDEXEC"
done < $1

SEDEXEC="sed -e '$SEDEXEC' $2 > $3"
eval $SEDEXEC