Validate a string

Question

I'm not that good with regular expressions...

I need a JavaScript regular expression that will do the following:

The string can contain letters (upper and lower case), but not punctuations such as éàïç...
The string can contain numbers (0..9) anywhere in the string, except on the first position.
The string can contain underscores (_).

Valid strings:

foo
foo1
foo_bar
fooBar

Invalid strings:

1foo --> number as first character
foo bar --> space
föo --> punctuation ö

Many thanks!

Are you looking for a CSS identifier validator? Although some validation rules are missing, this comes very close. — BalusC
– BalusC, Commented May 19, 2010 at 19:28
Nah it's for a naming system. These are my rules to "simplify" readability of those names. — Activist
– Activist, Commented May 19, 2010 at 19:32

BalusC · Accepted Answer · 2010-05-19 22:09:25Z

9

This regex should do what you need:

/^[a-z_]+[\w]*$/i

Use it as follows:

var match = /^[a-z_]+[\w]*$/i.test(string);

Some explanation:

/      : start of JavaScript regex pattern
^      : start of string
[a-z_] : only alphabetic characters or underscore
+      : one or more
[\w]   : any word-character (aplhanumeric and the underscore)
*      : zero or more
$      : end of string
/      : end of JavaScript regex pattern
i      : case insensitive modifier

To learn more about regular expressions, you may find this site useful.

edited May 19, 2010 at 22:09

answered May 19, 2010 at 19:32

BalusC

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2 Comments

adamJLev Over a year ago

Just needs an underscore in the [a-z]: [a-z_]

BalusC Over a year ago

Yes, if the underscore may appear anywhere, then the [a-z] should indeed be [a-z_]. Hmm, actually, you're right he didn't explicitly forbid the underscore in the front. Updated answer.

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