We are very fortunate, indeed, to have others teach us as you do. Here are some supplemental links.
Regular Expressions http://lib.stat.cmu.edu/scgn/v52/section1_7_0_1.html Regular Expressions http://sunsite.auc.dk/frexxed/docs/FrexxEd_Sections/regular_expressions.HTML Thank you. Art Lemasters > lucier wrote: > > > > Howdy all.....:-) > > > > During a chat with a linux developer, he mentioned that OS/2 (plus DOS and > > > > Windows) didn't support "regular expressions". From what I have been able > > to > > gather from reading app docs (like the EPM INF file) , *nix ported to OS/2 > > app > > docs and shareware descriptions, it would appear that OS/2 does indeed > > support > > regular expressions. > > > > 1) What is the definition of "regular expressions"? (A url to grab a > > tutorial > > would also be great) > > > > 2) Are there any great differences between the way(s) that Linux supports > > > > (integrates???) regular expressions and the way OS/2 does? > > > > 3) A couple of messages I ran across on DejaNews seemed to imply that REXX > > > > supports regular expressions. Would this be an integrated function of REXX > > or > > just indicative that a person could 'roll their own" with REXX? > > > > Any thoughts on the above would be appreciated.........:-) > > Whirlwind lecture follows (feel free to correct me, I lost my textbook): > > In computer science, regular expressions are at the heart of formal languages. > Languages can be described by grammars, regular expressions, or recognizers. > Each is equivalent to the other two: if you have a regular expression, you can > construct a grammar or recognizer, etc. > > Grammar: a set of rules for generating a string. Eg: if you have an A, you can > replace it with AA. > > Regular expression: Eg: A* the `*' is a Kleine star and means you may have > zero > or one or more of the preceding regular expressions (in this case A). > > Recognizer: this would be a machine (ie, software) that takes any string and > returns a yes or no answer to the question "is this string a member of the > language of all strings of As?" > > In each of the three above cases, the language used is the language of all > strings with only As: A, AA, AAA, AAAA... Having three ways to describe that > language is useful. > > With study you learn that languages can be grouped into classes depending on > their "power." For instance, simple languages can be recognized by simpler > machines than more complex languages. Regular languages are of course easier > to > deal with than non-regular languages. > > You can transform common problems into languages, and vice versa. Since they > fall into language classes, that is how we say one problem is "harder" than > another: it requires a fundamentally more powerful machine to solve > (recognize) > it. For instance, you can solve more problems with two stacks than with one, > but > having two tapes gives you no more power than one. > > This notion has been formalized as the language sets NP-HARD and NP-COMPLETE, > and P. We theorize that P=NP but have yet to prove or disprove it. These are > just statements about the theoretical maximum "hardness" of problems. We also > theorize that tape (Turing) machines are the most powerful, and can recognize > the hardest languages to recognize (I forget which... context-sensitive?). > > Anyways, the important point is that when you use a regular expression in > grep, > it transforms it into a little machine (code) that it runs on every line to > see > whether that line is in the "language" of strings you are searching for. > > Hope I haven't confused anybody. > > > > -- > SEGV It is now safe to uninstall > Windows: > http://www.cgocable.net/~mlepage/ > http://www.debian.org/ > > > -- > To UNSUBSCRIBE, email to [EMAIL PROTECTED] > with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED] > > -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
