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I know JavaScript regular expressions can ignore case for the entire match, but what about just the first character? Then hello World! would match Hello World! but not hello world!.

I know JavaScript regular expressions can ignore case for the entire match, but what about just the first character? Then hello World! would match Hello World! but not hello world!.

• javascript
• regex

Share Improve this question Follow edited Apr 25, 2010 at 11:44 hoju asked Apr 25, 2010 at 4:46 hojuhoju 29.5k4040 gold badges137137 silver badges178178 bronze badges 1

• 1 @Richard: you keep menting that it's not what you want but can you more precise? Basically from your question, just take your "regular expression that can be applied to all words" [sic] and that doesn't work (or you wouldn't be asking the question) and add [a-zA-Z] in front of it... – SyntaxT3rr0r Commented Apr 25, 2010 at 5:29

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5 Answers 5

Sorted by: Reset to default 6

You mean like /[Tt]uesday/

The [Tt] creates a set, which means either 'T' or 't' can match that first character.

Do it another way. Force the first character of your data string to lower case before matching it against your regular expression. Here's how you'd do it in ActionScript, JavaScript should be similar:

var input="Hello World!";
var regex=/hello World!/;
var input2 = input.substr(0, 1).toLowerCase() + input.substr(1);
trace(input2.match(regex));

[a-zA-Z]{1}[a-z]

Your question doesn't really make sense. Since the edit, it now says "I am after a general regular expression that can be applied to all words.". The regex to match all words and punctuation would be ".*"

What are you trying to match? Can you give examples of what should match and what should not match?

regular-expressions.info

• Character Classes or Character Sets

  With a "character class", also called "character set", you can tell the regex engine to match only one out of several characters. Simply place the characters you want to match between square brackets. If you want to match an a or an e, use [ae]. You could use this in gr[ae]y to match either gray or grey.

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Thus, a regex that matches Tuesday and tuesday, and nothing else, is [Tt]uesday.

---

If you're given an arbitrary word w, and a subject s that needs to match w, except that the first letter is case-insensitive, then you don't really need regular expressions. Just check that the first letter of w and s is the same letter, ignoring case, then make sure that the substring of w and s from index 1 matches exactly.

In Java, it'd look something like this:

boolean equalsFirstLetterIgnoreCase(String s, String w) {
   return s.substring(0, 1).toLowerCase().equals(w.substring(0, 1).toLowerCase())
     && s.substring(1).equals(w.substring(1));
}

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