How to combine RegEx conditions?

Question

I need to make a QLineEdit with a QRegularExpressionValidator with the following 3 constraints:

1. Cannot start with empty space ^[\\S]
2. Cannot start with Hello ^(?!Hello).+
3. Cannot end with empty space ^.*[\\S]$

How do I combine those 3 in one regex so that I can set it a QRegularExpressionValidator?

Thank you!

Note: As long as I have a regex that is verifiable with a regex tool I am good. I have specified Qt just to provide more context.

Answer 1

You could use

^(?!Hello\b)\S(?:.*\S)?$

Explanation

• ^ Start of string
• (?!Hello\b) Negative lookahead, assert what is directly to thte right is not Hello
• \S Match a non whitespace char
• (?:.*\S)? Optionally match 0+ times any char except a newline and a non whitespace char
• $ End of string

Regex demo