encode string with spaces

All - Any easy way to take a string and fill the spaces in it? Say like a URLencoding: This is my dog, Jack becomes This%20is%20my%20dog,%20Jack I ask this as I would like to send a string to a perl function that can parse the string and create a hash from it based on delimiters I define. But if there are spaces in the string in between defined fields, it is thrown off. BTW, I tried both ereg_replace() and str_replace() with no luck as below: $my_string = "This is my dog, Jack"; str_replace(" ", "%20", $my_string); $my_string remains with spaces, not %20s. Thanks. Kevin McCarthy