#!perl -w
use strict;

my $searchString = '$a';
my $replaceString = '$b';
my $string = '$a($a hi) $a (($a))$a';

# get positions of chars to care about
my @aPos = &GetCharPositions($string, $searchString);;
my @lparants = &GetCharPositions($string, '(');
my @rparants = &GetCharPositions($string, ')');
print "String: $string\n";
print "LeftP:  @lparants\n";
print "RightP: @rparants\n";

die "Error: non equal paranthesis found\n" if ($#lparants != $#rparants);
print "@aPos\n";

# filter stuff between parantheses
foreach my $i (0..$#lparants){
    @aPos = grep { $_ < $lparants[$i] or $_ > $rparants[$i] } @aPos;
    print "AP: @aPos\n";
}

# do replacement of stuff still in @aPos
foreach (@aPos){
    substr($string, $_, length($searchString)) = $replaceString;
    print "S: $string\n";
}


# ------------------------------------------------------------
sub GetCharPositions {
    my ($string, $subString) = @_;
    my @list = ();

    my $startPos = -1;
    my $pos;
    while ( defined ($pos = index($string, $subString, $startPos+1))){
	last if $pos == -1;
	$startPos = $pos;
	push (@list, $pos);
    }
    return (@list);
} # GetCharPositions
# ----------------------------------------------------