Is there a regular expression that return substrings from a string, that do not match a given list of specific substrings?

Question

Hi I am wondering if there is a regular expression that can do the following:

Select all the substrings from a string that :

start with & and
have n number of characters after the & (n >= 0)

AND those substrings are NOT

&
'
<
> or
"

For example, given the string

&apos;Stewie &amp; Brian    &partners in crime;&apos;

is there a regex that will return only the substring &partners ?

My intuition says no , because I need a context free grammar but how can I prove that? Is there a regex to test it with the pumping lemma ?

Or a regex actually exists and my intuition is just wrong?

Thank you

Hi, I've taken the liberty to reformat your post. By placing short texts between backticks, you can format them as code (so you don't need to insert a space between `&` and `apos;` in order to keep the literal text). Longer texts and multi-line code samples can be formatted that way by indenting them by four spaces. Both can be achieved by selecting the text and pressing Ctrl-K. You might want to look at the editor help for more of these formatting tips. Aside from that, welcome to StackOverflow! — Tim Pietzcker, Jan 08 '16 at 16:53

score 2 · Accepted Answer · answered Jan 08 '16 at 16:46

2

Sure:

&(?!(amp|apos|lt|gt);)\S{4,}

for n=4

See live demo.

The key here is the negative look ahead (?!(amp|apos|lt|gt);), which asserts (without consuming input) that the input immediately following does not match (amp|apos|lt|gt);

answered Jan 08 '16 at 16:46

Bohemian

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Is there a regular expression that return substrings from a string, that do not match a given list of specific substrings?

1 Answers1