unable to regex certain pattern (part 2)

Question

Cont from unable to regex certain pattern

I have the following regular expression:

^(?!.*  )[^#+&\'\"\\\\]*$

Now I want to fulfill the followings:

""      ---> invalid
" "     ---> invalid
" a"    ---> invalid
"a b"   ---> valid
"a  b"  ---> invalid

Can someone help me?

you want a regex that contains just one space, and not the excluded char you gave, right? — Thomas Ayoub, Jul 20 '16 at 07:52
Is a finishing space valid? Is it allowed to have multiple spaces in a string like `a b c`? — Sebastian Proske, Jul 20 '16 at 08:06
I think you need [`^[^#+&'"\\\s]+(?:\s[^#+&'"\\\s]+)*$`](https://regex101.com/r/gB4bY6/1) — Wiktor Stribiżew, Jul 20 '16 at 08:09
@SebastianProske finishing space invalid...for the second part, yes, it allowed... but no double spaces between a and b or b and c ... — KKL Michael, Jul 20 '16 at 08:13

Thomas Ayoub · Answer 1 · 2016-07-20T12:32:07.213

1

You can use this regex:

^(?!^.*\s{2}.*$)[^\s][^#+&'"\\\n\r]*[^\s]$

In php:

$re = "/^(?!^.*\\s{2}.*$)[^\\s][^#+&'\"\\\\\\n\\r]*[^\\s]$/m";

See demo

(?!^.*\s{2}.*$) will ensure that the string doesn't contains consecutive spaces.

^[^\\s][^#+&'\"\\\\\\n\\r]*[^\\s]$ will ensure that the string doesn't contain leading nor trailing spaces.

edited Jul 20 '16 at 12:32

answered Jul 20 '16 at 08:00

Thomas Ayoub

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Wiktor Stribiżew · Answer 2 · 2016-07-20T08:16:51.400

You can use

^[^#+&'"\\\s]+(?:\s[^#+&'"\\\s]+)*$

PHP:

$re = '~^[^\s#+&\'"\\\\]+(?:\s[^\s#+&\'"\\\\]+)*$~';

See the regex demo. This regex does not allow consequent whitespaces and any leading/trailing whitespaces, is linear and fast.

Details:

^ - start of string
[^#+&'"\\\s]+ - 1+ chars other than whitespace and any of #, +, &, ', ", \ chars
(?:\s[^#+&'"\\\s]+)* - zero or more sequences of:
- \s - whitespace (1 time)
- [^#+&'"\\\s]+ - 1+ chars other than whitespace and any of #, +, &, ', ", \ chars
$ - end of string (replace with \z for safer matching)

Here is an IDEONE PHP demo that only echos Matched 'a b':

if (preg_match('~^[^\s#+&\'"\\\\]+(?:\s[^\s#+&\'"\\\\]+)*$~', "")) {
    echo "Matched ''\n";
}
if (preg_match('~^[^\s#+&\'"\\\\]+(?:\s[^\s#+&\'"\\\\]+)*$~', " ")) {
    echo "Matched ' '\n";
}
if (preg_match('~^[^\s#+&\'"\\\\]+(?:\s[^\s#+&\'"\\\\]+)*$~', " a")) {
    echo "Matched ' a'\n";
}
if (preg_match('~^[^\s#+&\'"\\\\]+(?:\s[^\s#+&\'"\\\\]+)*$~', "a b")) {
    echo "Matched 'a b'\n";
}
if (preg_match('~^[^\s#+&\'"\\\\]+(?:\s[^\s#+&\'"\\\\]+)*$~', "a  b")) {
    echo "Matched 'a  b'\n";
}

unable to regex certain pattern (part 2)

2 Answers2