Regex for CamelCased words with leading uppercase letter

Question

How do I find all CamelCased words in a document with a regular expression? I'm only concerned with leading Upper camel case (i.e., camel cased words in which the first letter is capitalized).

Answer 1

([A-Z][a-z0-9]+)+

Assuming English. Use appropriate character classes if you want it internationalizable. This will match words such as "This". If you want to only match words with at least two capitals, just use

([A-Z][a-z0-9]+){2,}

UPDATE: As I mentioned in a comment, a better version is:

[A-Z]([A-Z0-9]*[a-z][a-z0-9]*[A-Z]|[a-z0-9]*[A-Z][A-Z0-9]*[a-z])[A-Za-z0-9]*

It matches strings that start with an uppercase letter, contain only letters and numbers, and contain at least one lowercase letter and at least one other uppercase letter.

Answer 2

Lower camel case

this regex includes number and implements strict lower camel case as defined by the Google Java Style Guide regex validation.

[a-z]+((\d)|([A-Z0-9][a-z0-9]+))*([A-Z])?

1. The first character is lower case.
2. The following elements are either a single number or a upper case character followed by lower cases characters.
3. The last character can be an upper case one.

Here is a snippet illustrating this regex. The following elements are valid.

xmlHttpRequest
newCustomerId
innerStopwatch
supportsIpv6OnIos
youTubeImporter
youtubeImporter
affine3D

Upper camel case

Same principle as the one used for lower camel case with always a starting upper case character.

([A-Z][a-z0-9]+)((\d)|([A-Z0-9][a-z0-9]+))*([A-Z])?

Here is a snippet illustrating this regex. The following elements are valid.

XmlHttpRequest
NewCustomerId
InnerStopwatch
SupportsIpv6OnIos
YouTubeImporter
YoutubeImporter
Affine3D

Answer 3

Adam Crume's regex is close, but won't match for example IFoo or HTTPConnection. Not sure about the others, but give this one a try:

\b[A-Z][a-z]*([A-Z][a-z]*)*\b

The same caveats as for Adam's answer regarding digits, I18N, underscores etc.

You can test it out here.

Answer 4

The regexp that solved my problem (properly naming directories that will be recognized by FitNesse DbFit web service) is:

(^[A-Z][a-z0-9]+[A-Z]$)|(^[A-Z][a-z0-9]+([A-Z][a-z0-9]+)+$)|(^[A-Z][a-z0-9]+([A-Z][a-z0-9]+)+[A-Z]$) 

I reverse engineered these particular CamelCase rules, they are:

1. First character uppercase alpha
2. Next 1-n characters lowercase alphanumeric
3. Next character (n+1) uppercase alpha
4. Next 0 or more characters lowercase alphanumeric
No consecutive uppercase; no special characters.
Pattern may be repeated, e.g. NoChildLeftBehindSuite9102

The expression passed my testing as follows:

Camel01C is CamelCase syntax
Camel01c01 is not CamelCase syntax
Camel01C01 is CamelCase syntax
Camel01CC01 is not CamelCase syntax
Camel0a1c1 is not CamelCase syntax
Camel0a1C1 is CamelCase syntax
Camel0ac1b1C1 is CamelCase syntax
CamelC is CamelCase syntax
CamelC1 is CamelCase syntax
CamelCA is not CamelCase syntax
CamelCa1 is CamelCase syntax
CamelCa_1 is not CamelCase syntax
IbsReleaseTestVerificationRegressionSuite is CamelCase syntax
IbsReleaseTestVerificationRegressioNSuite is not CamelCase syntax
IbsReleaseTestVerificationRegressioN is CamelCase syntax

Answer 5

This seems to do it:

/^[A-Z][a-z]+([A-Z][a-z]+)+/

I've included Ruby unit tests:

require 'test/unit'

REGEX = /^[A-Z][a-z]+([A-Z][a-z]+)+/

class RegExpTest < Test::Unit::TestCase
  # more readable helper
  def self.test(name, &block)
    define_method("test #{name}", &block)
  end

  test "matches camelcased word" do
    assert 'FooBar'.match(REGEX)
  end

  test "does not match words starting with lower case" do
    assert ! 'fooBar'.match(REGEX)
  end

  test "does not match words without camel hump" do
    assert ! 'Foobar'.match(REGEX)
  end

  test "matches multiple humps" do
    assert 'FooBarFizzBuzz'.match(REGEX)
  end
end

Answer 6

([A-Z][a-z\d]+)+

Should do the trick for upper camel case. You can add leading underscores to it as well if you still want to consider something like _IsRunning upper camel case.

Answer 7

Just modified one of @AdamCrume's proposals:

([A-Z]+[a-z0-9]+)+

This will match IFrame, but not ABC. Other camel-cased words are matched, e.g. AbcDoesWork, and most importantly, it also matches simple words that do not have at least another capitalized letter, e.g. Frame.

What do you think of this version? Am I missing some important case?

Answer 8

([a-z0-9]+|[A-Z0-9]+[a-z0-9]*|[A-Z0-9][a-z0-9]*([A-Z0-9][a-z0-9]*)*)

java regex to match string on camel case.