Regular expression not case sensitive ruby
A regular expression can only act as a rudimentary filter. It isn’t even smart enough to handle even That is no better than all the other non-RFC patterns. There is some danger that common usage and widespread sloppy coding will establish a de facto standard for e-mail addresses that is more restrictive than the recorded formal standard. Validate an E-Mail Address with PHP, the Right Way After all, anybody can put down and that will even parse as legal, but it isn't likely to be the person at the other end.įor PHP, you should not use the pattern given in This is why most mailing lists now use that mechanism to confirm sign-ups. Fixing that requires a fancier kind of validation that involves sending that address a message that includes a confirmation token meant to be entered on the same web page as was the address.Ĭonfirmation tokens are the only way to know you got the address of the person entering it. People sign others up to mailing lists this way all the time. It's also important to understand that validating it per the RFC tells you absolutely nothing about whether that address actually exists at the supplied domain, or whether the person entering the address is its true owner. However, if you are forced to use one of the many less powerful pattern-matching languages, then it’s best to use a real parser. Python and C# can do that too, but they use a different syntax from those first two. The more sophisticated patterns in Perl and PCRE (regex library used e.g. for above regexp which is more clear than regexp itself (Scrape the rendered version, not the markdown, for actual is The rest of it appears to be consistent with the RFC 5322 grammar and passes several tests using grep -Po, including cases domain names, IP addresses, bad ones, and account names with and without quotes.Ĭorrecting the 00 bug in the IP pattern, we obtain a working and fairly fast regex. One RFC 5322 compliant regex can be found at the top of the page at but uses the IP address pattern that is floating around the internet with a bug that allows 00 for any of the unsigned byte decimal values in a dot-delimited address, which is illegal. RFC 5322 leads to a regex that can be understood if studied for a few minutes and is efficient enough for actual use. Fortunately, RFC 822 was superseded twice and the current specification for email addresses is Note: A regexp can't use named backreferences and numbered backreferences simultaneously.Is inefficient and obscure because of its length. Named groups can be backreferenced with \k, where name is the group name. match( "The cat sat in the hat") #=> 'at'Ĭapture groups can be referred to by name when defined with the (?) or (?' name ') constructs. Regexp#match returns a MatchData object which makes the captured text available with its method: /(.) \1 in/. 'at' is captured by the first group of parentheses, then referred to later with \1: /(.) \1 in/. Within a pattern use the backreference \n outside of the pattern use MatchData. The text enclosed by the nth group of parentheses can be subsequently referred to with n. They behave like greedy quantifiers, but having matched they refuse to “give up” their match even if this jeopardises the overall match. match( "") #=> #">Ī quantifier followed by + matches possessively: once it has matched it does not backtrack. The first uses a greedy quantifier so '.+' matches '' the second uses a lazy quantifier so '.+?' matches '': //. A greedy metacharacter can be made lazy by following it with ?.īoth patterns below match the string. By contrast, lazy matching makes the minimal amount of matches necessary for overall success. Repetition is greedy by default: as many occurrences as possible are matched while still allowing the overall match to succeed. Regexps are created using the /./ and %ro/) #=> # A Regexp holds a regular expression, used to match a pattern against strings.