Regular Expressions in CoffeeScript are Awesome

His example, slightly modified for Perl:<p><pre><code> my $emailPattern = qr{ ^ #begin of line ([a-z0-9_.-]+) #one or more letters, numbers, _ . or - @ #followed by an @ sign ([\da-z.-]+) #then one or more letters, numbers, _ . or - \. #followed by a period ([a-z.]{2,6}) #followed by 2 to 6 letters or periods $ }xi; #end of line and ignore case if( 'john.smith@gmail.com' =~ $emailPattern ){ print "E-mail is valid\n"; } else { print "E-mail is invalid\n"; } </code></pre> EDIT: A much better way of doing it though:<p><pre><code> use Mail::Sendmail; if( 'john.smith@gmail.com' =~ /$Mail::Sendmail::address_rx/ ){ print "E-mail is valid\n"; } else { print "E-mail is invalid\n"; }</code></pre>

In JS you can comment regular expressions, too... :)<p><pre><code> var foo = new RegExp( '\\d\+' + // First digit '-' + // Delimiter '\\d\+' // Second digit ); foo.test("1234-5432");</code></pre>

For a little dollop of recursivity in your morning coffee, here's the bit where the CoffeeScript compiler uses these extended regular expressions to lex, among other things, extended regular expressions...<p><a href="https://github.com/jashkenas/coffee-script/blob/master/src/lexer.coffee#L595-647" rel="nofollow">https://github.com/jashkenas/coffee-script/blob/master/src/l...</a>

I know the email validation was just an example, but since we're on the subject, if you've got an email validation that includes a maximum number of characters for the TLD you might want to update that before the new TLDs start rolling in later this year or next.

Python, too:<p><a href="http://docs.python.org/library/re.html#re.VERBOSE" rel="nofollow">http://docs.python.org/library/re.html#re.VERBOSE</a><p><pre><code> a = re.compile(r"""\d + # the integral part \. # the decimal point \d * # some fractional digits""", re.X) b = re.compile(r"\d+\.\d*")</code></pre>

Perl, Ruby and some other languages support a similar 'extended' RegEx syntax which allows comments and disregards whitespace (in Ruby, you use the 'x' flag on a Regexp literal).<p>For those using plain JavaScript -- or wanting to do a one-off conversion -- I wrote a simple JS function that converts an extended RegEx to a plain one:<p><a href="http://blog.mackerron.com/2010/08/08/extended-multi-line-js-regexps/" rel="nofollow">http://blog.mackerron.com/2010/08/08/extended-multi-line-js-...</a>

You shouldn't validate emails by regular expressions since, technically (at least according to spec)<p>"()&#60;&#62;[]:;@,\\\"!#$%&#38;'*+-/=?^_`{}| ~ ? ^_`{}|~."@example.org<p>is a perfectly valid email address [1]<p>[1] <a href="http://en.wikipedia.org/wiki/Email_address#Valid_email_addresses" rel="nofollow">http://en.wikipedia.org/wiki/Email_address#Valid_email_addre...</a>

"Let's face it, regular expressions aren't for everyone."<p>Wait, since when aren't they? I would have thought basic regex skills were a baseline shibboleth of a programmer. I even know several non-technical people that are proficient.

That has nothing to do CoffeeScript, most regex parser implementation support this via a flag. I've seen it done in PHP, Ruby, Perl, Objective-C. For languages whose regular expression engine don't support this, it's easy enough to achieve it via string concatenation.

I personally don't find this example very helpful in showing why I would do this. The regex is simple enough and to me the comments are the equivalent of "return here", needless and distracting.

What about trailing spaces? They need to be escaped by parenthesis?

is there any performance penalty?