Capitalized Words with Regular Expression

Question

I'm new to RegEx and I'm looking for a way to match sentences where the first letter is capitalized and the rest is in lowercase.

I've tried a couple of things (IF statements included), but just can't seem to get it.

This is my last version:

(([A-Z])([a-z]+\s|[a-z]+))+

I thought it worked at first, but is now accepting capitalized letters in the middle of the word.

The Output Would Be Like This (Each Word Capitalized).

Thanks!!

Answer 1

To match whole strings that start with an uppercase letter and then have no uppercase letters use

^[A-Z][^A-Z]*$

See the regex demo. ^ matches the start of string, [A-Z] matches the uppercase letters, [^A-Z]* matches 0 or more chars other than uppercase letters and $ matches the end of string.

To match capitalized words, you may use

\b[A-Z][a-zA-Z]*\b

where \b stands for word boundaries. See the regex demo.

In various regex flavors, there are other ways to match word boundaries:

• bash,r (TRE, base R): \<[A-Z][a-zA-Z]*\>
• postgresql, tcl: \m[A-Z][a-zA-Z]*\M or \y[A-Z][a-zA-Z]*\y
• bash, mysql (MySQL versions before 8): [[:<:]][A-Z][a-zA-Z]*[[:>:]]

Also, you may consider using [[:upper:]] or \p{Lu} instead of [A-Z] and [[:alpha:]] or \p{L} instead of [a-zA-Z] to match any Unicode uppercase letters or any letters correspondingly.

See this demo and this demo, too.

Answer 2

The expression accepts capital letters in the middle of the world because now the spaces between words are optional, and words can run into each other.

You can take a more structured approach: a sentence must have at least one word. That's

[A-Z][a-z]*

After that initial word you can get any number of more words, each preceded by whitespace. So in total:

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