Validating string using RegEx

Question

I need a Regular expression to validate string for below rules.

String should not contain any repeated characters more than 2 times.
String should not allow special characters like &, <, %

So far I managed to create regular expression

/(?!(.)\1{2,})^([a-zA-Z0-9''\.\-\,]+\s?)*$/i

which validates rules 1 & 2. But only problem what I have is it only validates rule at the start of string.

Any feedback on the two answers you received?

Thomas Ayoub
– Thomas Ayoub

2016-09-27 08:04:16 +00:00
Commented Sep 27, 2016 at 8:04 — Thomas Ayoub
– Thomas Ayoub, Commented Sep 27, 2016 at 8:04

Thomas Ayoub · Accepted Answer · 2016-09-26 17:54:46Z

2

Change your regex to

/(?!.*(.)\1{2,})^([a-zA-Z0-9'".,-]+\s?)*$/i
    ^^

It will allow the negative lookahead to work on the whole regex instead of the beginning.

See demo

edited Sep 26, 2016 at 17:54

answered Sep 26, 2016 at 17:29

Thomas Ayoub

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2 Comments

Tân Over a year ago

Why isn't [a-zA-Z0-9] [\w]?

Thomas Ayoub Over a year ago

@HappyCoding because \w also include the _

Aaron · Accepted Answer · 2016-09-26 17:29:09Z

2

For your negative lookahead to work, you have to make it so it could match a 3-in-a-row at any place in the validated string ; just add a .* at its start :

/(?!.*(.)\1{2,})^([a-zA-Z0-9'".\-,]+\s?)*$/i

I also changed your two consecutive single-quotes in your character class to the single-quote and double quote I assume you want to allow and removed unnecessary backslashes escapes.

answered Sep 26, 2016 at 17:29

Aaron

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