The interpreter is the "engine" that executes scripts.
Regular expressions are used in other languages, so you
only need an interpreter for that language.
For scripting languages without built-in regular expression
support, you'll need additional software, like Patrick McPhee's
for Rexx, or
EDIT (MS-DOS), Notepad (Windows), E (OS/2), or any
other ASCII editor will do, as will your
editor or IDE for your
Like the scripts themselves, a regular expression is "just"
a string of text.
To help you write your regular expressions, several
expression builders &
evaluators are available.