Professional Information Technology-Programming Book part 101 pps

Send personal email to ben@forta.com. For questions about a book use support@forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't it be nice if it were that simple, huh?). \w+@\w+\.\w+ Send personal email to ben@forta.com. For questions about a book use support@forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't it be nice if it were that simple, huh?). The pattern matched all three addresses correctly. The regular expression first matches one or more alphanumeric characters using \w+. Next it matches @ followed by one or more characters, again using \w+. It then matches . (using the escaped \.) and another \w+ to match the end of the address. Tip + is a metacharacter. To match a + you'll need to escape it as \+. + can also be used to match one or more sets of characters. To demonstrate this, the following example shows the same regular expression but with slightly different text: Send personal email to ben@forta.com or ben.forta@forta.com. For questions about a book use support@forta.com. If your message is urgent try ben@urgent.forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't it be nice if it were that simple, huh?). \w+@\w+\.\w+ Send personal email to ben@forta.com or ben.forta@forta.com. For questions about a book use support@forta.com. If your message is urgent try ben@urgent.forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't it be nice if it were that simple, huh?). The regular expression matched five addresses, but two of them are incomplete. Why is this? \w+@\w+\.\w+ makes no accommodations for . characters before the @, and it allows only a single . separating the two strings after the @. Although ben.forta@forta.com is a perfectly legal email address, the regular expression matched only forta (instead of ben.forta) because \w matches alphanumeric characters but not a . in the middle of a string of text. What we need here is to match either \w or ., or in regular expression parlance, a set of [\w\.]. Following is a revised example: Send personal email to ben@forta.com or ben.forta@forta.com. For questions about a book use support@forta.com. If your message is urgent try ben@urgent.forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't it be nice if it were that simple, huh?). [\w.]+@[\w.]+\.\w+ Send personal email to ben@forta.com or ben.forta@forta.com. For questions about a book use support@forta.com. If your message is urgent try ben@urgent.forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't it be nice if it were that simple, huh?). That seemed to do the trick. [\w.]+ matches one or more instances of any alphanumeric character, underscore, and ., and so ben.forta is matched. [\w.]+ is also used for the string after the @ so that deeper domain (or host) names are matched. Note Notice that for the final match, you used \w+ and not [\w.]+. Can you figure out why? Try using [\w.] for the final pattern and see what is wrong with the second, third, and fourth matches. Note You'll notice that the . in the set was not escaped, and it matched . anyway (it was treated as a literal as opposed to a metacharacter). Generally, metacharacters such as . and + are considered to be literal text when used within sets, and therefore they need not be escaped. However, escaping them does no harm. [\w.] is functionally equivalent to [\w\.]. Matching Zero or More Characters + matches one or more characters. Zero characters will not match—there has to be at least one. But what if you wanted to match entirely optional characters so that zero characters would be allowed? To do this, you use the * metacharacter. * is used exactly like +; it is placed right after a character or a set and will match zero or more instances of the character or set. Therefore, pattern B.* Forta would match B Forta, B. Forta, Ben Forta, and other combinations, too. To demonstrate the use of +, take a look at a modified version of the email example: Hello .ben@forta.com is my email address. [\w.]+@[\w.]+\.\w+ Hello .ben@forta.com is my email address. You will recall that [\w.]+ matches one or more instances of alphanumeric characters and ., and so .ben matched. There is obviously a typo in the preceding text (an extraneous period in the middle of the text), but that is irrelevant. The bigger issue is that although . is a valid character in an email address, it is not a valid character with which to start an email address. In other words, what you really need to match is alphanumeric text with optional additional characters, like this: Hello .ben@forta.com is my email address. \w+[\w.]*@[\w.]+\.\w+ Hello .ben@forta.com is my email address. . Send personal email to ben@forta.com. For questions about a book use support@forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't. huh?). w+@w+.w+ Send personal email to ben@forta.com. For questions about a book use support@forta.com. Feel free to send unsolicited email to spam@forta.com (wouldn't. text: Send personal email to ben@forta.com or ben.forta@forta.com. For questions about a book use support@forta.com. If your message is urgent try ben@urgent.forta.com. Feel free