Regex to detect one of several strings

I've got a list of email addresses belonging to several domains. I'd like a regex that will match addresses belonging to three specific domains (for this example: foo, bar, & baz)

So these would match:

1. a@foo
2. a@bar
3. b@baz

This would not:

1. a@fnord

Ideally, these would not match either (though it's not critical for this particular problem):

1. a@foobar
2. b@foofoo

Abstracting the problem a bit: I want to match a string that contains at least one of a given list of substrings.

Use the pipe symbol to indicate "or":

/a@(foo|bar|baz)\b/

If you don't want the capture-group, use the non-capturing grouping symbol:

/a@(?:foo|bar|baz)\b/

(Of course I'm assuming "a" is OK for the front of the email address! You should replace that with a suitable regex.)

^(a|b)@(foo|bar|baz)$

if you have this strongly defined a list. The start and end character will only search for those three strings.

Use:

/@(foo|bar|baz)\.?$/i

Note the differences from other answers:

• \.? - matching 0 or 1 dots, in case the domains in the e-mail address are "fully qualified"
• $ - to indicate that the string must end with this sequence,
• /i - to make the test case insensitive.

Note, this assumes that each e-mail address is on a line on its own.

If the string being matched could be anywhere in the string, then drop the $, and replace it with \s+ (which matches one or more white space characters)

should be more generic, the a shouldn't count, although the @ should.

/@(foo|bar|baz)(?:\W|$)/

Here is a good reference on regex.

edit: change ending to allow end of pattern or word break. now assuming foo/bar/baz are full domain names.

If the previous (and logical) answers about '|' don't suit you, have a look at

http://metacpan.org/pod/Regex::PreSuf

module description : create regular expressions from word lists

You don't need a regex to find whether a string contains at least one of a given list of substrings. In Python:

def contain(string_, substrings):
    return any(s in string_ for s in substrings)

The above is slow for a large string_ and many substrings. GNU fgrep can efficiently search for multiple patterns at the same time.

Using regex

import re

def contain(string_, substrings):
    regex = '|'.join("(?:%s)" % re.escape(s) for s in substrings)
    return re.search(regex, string_) is not None

Related

• Multiple Skip Multiple Pattern Matching Algorithm (MSMPMA) [pdf]

Ok I know you asked for a regex answer. But have you considered just splitting the string with the '@' char taking the second array value (the domain) and doing a simple match test

if (splitString[1] == "foo" && splitString[1] == "bar" && splitString[1] == "baz")
{
   //Do Something!
}

Seems to me that RegEx is overkill. Of course my assumption is that your case is really as simple as you have listed.