#! /bin/sh

if [ "$1" = "" -o "$3" = "" ]
then
    echo usage : $0 old_string new_string files ...
    exit 1
fi

old_string=$1
new_string=$2
shift
shift

echo substituing $old_string by $new_string in

while [ "$1" != "" ]
do
    echo -n $1 " : "
    tmpname=`basename $1`
    if [ ! -f "$1" ]
    then
        echo warning : $1 "doesn't exist"
        shift
        continue
    fi
    if [ -L "$1" ]
    then
        echo warning : $1 symbolic link, skipped
        shift
        continue
    fi
    if [ ! -w "$1" ]
    then
        echo warning : $1 non writable, skipped
        shift
       continue
    fi

    rm -f /tmp/substitute_$$_$1

    sed s/"$old_string"/"$new_string"/g < $1 > /tmp/substitute_$$_$tmpname

    if [ "$?" != "0" ]
    then
        echo error : sed failed on $tmpname
        rm -f /tmp/substitute_$$_$tmpname
        exit 1
    fi

    if [ ! -f "/tmp/substitute_$$_$tmpname" ]
    then
        echo error : sed failed on $tmpname
        exit 1
    fi

    diff -q $1 /tmp/substitute_$$_$tmpname >& /dev/null

    if [ "$?" = "0" ]
    then
        echo no change
        rm -f /tmp/substitute_$$_$tmpname
    else
        if [ "$?" = "1" ]
	then
	    echo changed
	    mv $1 $1.old
	    mv /tmp/substitute_$$_$tmpname $1
	else
	    echo "trouble ..."
	    rm -f /tmp/substitute_$$_$tmpname
	    exit 1
	fi
    fi
    shift
done