Construction of pattern that doesn't contain binary string

Question

I was trying to write a pattern which doesn't contain binary string (let's assume 101). I know that such expressions cannot be written using Regular Expression considering http://en.wikipedia.org/wiki/Regular_language.

I tried writing the pattern for the above problem using Regular Expression though and it seems to be working.

\b(?!101)\w+\b

What I wanted to ask is that can a regular expression be written for my problem and why? And if yes, then is my regular expression correct?

'Please also include a tag specifying the programming language or tool you are using.' (from `[regex]` tag description) — Lev Levitsky, Feb 24 '13 at 10:28
I am using an online tool http://regexpal.com/ for testing the `regex`. Though I am not employing it anywhere. — Sumit Gera, Feb 24 '13 at 10:30
Look at http://stackoverflow.com/questions/406230/regular-expression-to-match-string-not-containing-a-word — clapas, Feb 24 '13 at 10:56
The case is not similar. Some binary strings do not support `Regular Expressions`. — Sumit Gera, Feb 24 '13 at 11:14

score 0 · Answer 1 · answered Mar 19 '14 at 20:09

0

To match a whole string that doesn't contain 101:

^(?!.*101).*$

Look-ahead are indeed an easy way to check a condition on a string through regex, but your regex will only match alphanumeric words that do not start with 101.

answered Mar 19 '14 at 20:09

Robin

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score 0 · Answer 2 · answered May 30 '14 at 14:06

You wrote

I know that such expressions cannot be written using Regular Expression considering http://en.wikipedia.org/wiki/Regular_language.

In that Wikipedia article, you seem to have missed the

Note that the "regular expression" features provided with many programming languages are augmented with features that make them capable of recognizing languages that can not be expressed by the formal regular expressions (as formally defined below).

The negative lookahead construct is such a feature.

Construction of pattern that doesn't contain binary string

2 Answers2