regex to not match when string between two strings

Question

I have the following parsing scenario in python, there is cases of lines:

{{ name xxxxxxCONTENTxxxxx /}}
{{ name }} xxxxxxxCONTENTxxxxxxx {{ name /}}
{{ name xxxxxxCONTENTxxx {comand} xxxxCONTENTxxx /}}

All I need to do is classify to which case the given line belongs using regex.

I can successfully classify between 1) and 2) but having trouble to deal with 3).

to catch 1) I use:

re.match('\s*{{[^{]*?/}}\s*',line)

to catch 2) I use:

re.match('{{.*?}}',line)

and then raise a flag to keep the context since case 2) can be over multiple lines. How can I catch case 3) ??

The condition which I'm currently trying to match is to test for:

- start with '{{'
- end with '/}}'
- with no '{{' in between

However I'm having a hard time phrasing this in regex.

'^{{((?!{{).)*/}}$' - See Regular expression to match line that doesn't contain a word? — Tom Rees
– Tom Rees, Commented Apr 5, 2016 at 8:15
This works well in js but having trouble with it in python. In js it catches condition 1 and 2 which is good, but in python it gives no match. — Gerrie van Wyk
– Gerrie van Wyk, Commented Apr 5, 2016 at 8:33
Using pythex.org (great site btw :) ) I get that the regex matches 1 and 3, but not 2 - because it has '{{' in it. Could you post your code that didn't work? — Tom Rees
– Tom Rees, Commented Apr 5, 2016 at 8:45
Maybe {{(?:(?!{{).)*/}}? (maybe re.DOTALL is necessary if it spans across multiple lines) — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Apr 5, 2016 at 8:55
Could you please narrow your question to what you exactly need to match and what not to match? Do you want to match {{ name xxxxxxCONTENTxxxxx /}} and {{ name xxxxxxCONTENTxxx {comand} xxxxCONTENTxxx /}} as entire strings, and not match at all {{ name }} xxxxxxxCONTENTxxxxxxx {{ name /}}? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Apr 5, 2016 at 9:00

Wiktor Stribiżew · Accepted Answer · 2016-04-05 09:32:52Z

1

The conditions:

- start with '{{'
- end with '/}}'
- with no '{{' in between

are a perfect fit for a tempered greedy token.

^{{(?:(?!{{|/}}).)*/}}$
   ^^^^^^^^^^^^^^^^

See regex demo.

The (?:(?!{{|/}}).)* matches any text that is not {{ and /}} (thus matches up to the first /}}). Anchors (^ and $) allow to only match a whole string that starts with {{ and ends with /}} and has no {{ inside. Note that with re.match, you do not neet ^ anchor.

Now, to only match the 3rd type of strings, you need to specify that your pattern should have {....}:

^{{(?:(?!{{|/}}).)*{[^{}]*}(?:(?!{{|/}}).)*/}}$
   | ----  1 -----|| - 2 -||--------1-----|

See another regex demo

Part 1 is the tempered greedy token described above and {[^{}]*} matches a single {...} substring making it compulsory inside the input.

answered Apr 5, 2016 at 9:32

Wiktor Stribiżew

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