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Editorial Team
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Asked: 2026-06-12T09:30:33+00:00

Basically I’m creating a simple Interpreter for our compiler course. Of course this is

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Basically I’m creating a simple Interpreter for our compiler course. Of course this is not a homework-type question.

Anything that is followed by an asterisks is considered a comment provided that it is not part of the string. I have an escape character in my Interpreter which are brackets.

These are sample syntax for my interpreter

* hello world
OUTPUT: "This is asterisk [*]" * outputs string
OUTPUT: "This is asterisk *"  * outputs string produces syntax error
x = "[*]" & "hello" & "[*]*]" this is already comment which produces syntax error

when I try to run this Regex

[^\[]\*.*

It matches with the following:

* hello world
 * outputs string
 *"  * outputs string produces syntax error
]*]" this is already comment which produces syntax error

My question is, why did the regex “eats” one character before? Wherein I already need

* hello world
* outputs string
*"  * outputs string produces syntax error
*]" this is already comment which produces syntax error
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1 Answer

  1. Editorial Team

    You need to use zero width assertions to stop capturing the condition you just want to match, and
    not “eat” :

    (?<=[^\[])\*.*

    (?<=REGEX_CONDITION) ensures that matching is done, but the matched part ( NOT A “[” in your case) is not included in the matched result.

    Demo : http://regexr.com?32b99

    Edit: to make it fully working, I just added or condition on it

    (?<=[^\[])\*.*|^\*.*
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