How to combine RegEx conditions?

Question

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

Cannot start with empty space ^[\\S]
Cannot start with Hello ^(?!Hello).+
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.

Peter Thoeny · Answer 1 · 2020-07-25T23:41:19.267

1

This should do it:

var strings = [
  'a',
  'this is ok',
  ' leading space',
  'trailing space ',
  'Hello text',
  'Hello'
];
var re = /^([^\s]|(?!(Hello|\s)).*[^\s])$/;
strings.forEach((str) => {
  var val = re.test(str);
  console.log('"' + str + '" ==> ' + val);
});

Console output:

"a" ==> true
"this is ok" ==> true
" leading space" ==> false
"trailing space " ==> false
"Hello text" ==> false
"Hello" ==> false

Explanation of the regex:

^...$ -- anchor at the beginning and end
([^\s]|...) -- logical or, where the first part is a single non space char
(?!(...)).+ -- negative lookahead
(Hello|\s) -- ... of 'Hello' or space
.+[^\s] -- followed by any number of chars, except space at the end

edited Jul 25 '20 at 23:41

answered Jul 25 '20 at 00:30

Peter Thoeny

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It's working except that it expects at least two characters at the start of the string. Could you please fix that? So for instance if I just type "a" it should match, but I get no match. – santahopar Jul 25 '20 at 02:06
```^(?!(RBX|\\s)).+$``` this seems to solve it, but then the last requirement of not ending with an empty space does not meet. – santahopar Jul 25 '20 at 02:17
Updated the regex with example to allow a single non-space char. Please accept if this solves your question. – Peter Thoeny Jul 25 '20 at 04:37
Just typed "Hello" at https://regex101.com and it accepted, which it shouldn't. The single non-space character at the beginning is OK. – santahopar Jul 25 '20 at 05:52
Did you try to tweak the regex? Please, at last show us that you make an effort, not just ask. – Peter Thoeny Jul 25 '20 at 23:37
In any case, I updated the answer with a `'Hello'` test case. – Peter Thoeny Jul 25 '20 at 23:41
`Hello` should not be legal, with your regex it shows as if its legal. And I did try to tweak it, but with no success. Please look at the answer above. That one works. I have however voted up on your answer since it also gives valuable information. – santahopar Jul 26 '20 at 03:52
Fair enough. Run the code snippet, or test with regex101.com, and you can see that just `Hello` is a no match – Peter Thoeny Jul 27 '20 at 04:49
After your last edit yes, it does satisfy all the requirements, which is why I have voted up your answer anyways. But since "The fourth bird's" answer was correct from the very beginning, I chose his as the solution. I think it's only fair, don't you agee? – santahopar Jul 27 '20 at 20:49

score 1 · Accepted Answer · answered Jul 25 '20 at 09:33

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

How to combine RegEx conditions?

2 Answers2