如何检查字符串是否包含一个单词并且不包含另一个单词？

Question

I have a string like this:

$str = "this is a test";

I want to validate $str and return true if string is containing is and it isn't containing test. How can I do that?

---

Examples:

"this is a test"   // false
"this is a tes"    // true    "is" exists and "test" doesn't exist
"this iss a tes"   // false
"this iss a test"  // false

---

Here is my pattern \bis\b(?!test). But it seems to just checks existing, I mean it also returns true when test exists. I mean the result of following code us true which shouldn't be (because test exists).

if (preg_match ("/\bis\b(?!test)/","this is a test")) {
    return true;
} else {
    return false;
}

Note: I'm really insist on doing that by regex.

Answer 1

You can do it like this:

^                       # anchor it to the beginning of the line
    (?:(?!\btest\b).)*  # makes sure no test can be matched
    \bis\b              # match is as a word
    (?:(?!\btest\b).)*  # same construct as above
$                       # anchor it to the end of the line

See a demo on regex101.com.

For a PHP code, see the following snippet:

<?php
$string = "this is a test
this is a tes
this iss a tes
this iss a test
this test is";

$regex = '~
            ^                       # anchor it to the beginning of the line
                (?:(?!\btest\b).)*  # makes sure no test can be matched
                \bis\b              # match is as a word
                (?:(?!\btest\b).)*  # same construct as above
            $                       # anchor it to the end of the line
          ~mx';

preg_match_all($regex, $string, $matches);
print_r($matches);
?>

Hint: Note that I have changed the answer after it has been accepted to correct flaws in the original answer).