如果字符串以这些字符结尾，那么

I have the following string examples:

$text = 'Hello world. '; // true
$text = 'Hello world? '; // true
$text = 'Hello world! '; // true
$text = 'Hello world.   '; // true
$text = 'Hello world.'; // true

$text = 'Hello world '; // false
$text = 'Hello world'; // false
$text = 'Hello world-'; // false

If string ends with . or ? or !, then return true, otherwise, return false.

What's the best approach to this?

You can use substr, rtrim and strpos for this, like this:

$result = strpos("!?.", substr(rtrim($text), -1)) !== false;

This will set $result to true or false as you have indicated.

Assuming you're asking how you can test what the last character of the string is, you can use substr().

You can write an if statement like this:

<?php
// Test if the last character in the string is '!'.
if (substr($text, -1) === '!') {
    return true;
}

If you want to remove the blank spaces at the end of the string, you can use $text = trim($text) first.

If you want to test all the examples, you can use in_array() with an array containing all the characters you want to test.

if (in_array(substr(trim($text), -1), array('!', '.', '?', )) {
    return true;
}

Use preg_match to find those special string endings.

$text = array();
$text[] = 'Hello world. '; // true
$text[] = 'Hello world? '; // true
$text[] = 'Hello world! '; // true
$text[] = 'Hello world.   '; // true
$text[] = 'Hello world.'; // true

$text[] = 'Hello world '; // false
$text[] = 'Hello world'; // false
$text[] = 'Hello world-'; // false

foreach($text as $t) {
  echo "'" . $t . "' " . (hasSpecialEnding($t) ? 'true' : 'false') . "
";
}

function hasSpecialEnding($text) {
  return preg_match('/(\?|\.|!)[ ]*$/',$text);
}

Output:

'Hello world. ' true
'Hello world? ' true
'Hello world! ' true
'Hello world.   ' true
'Hello world.' true
'Hello world ' false
'Hello world' false
'Hello world-' false

You can see the code in action here: http://sandbox.onlinephpfunctions.com/code/51d839a523b940b4b4d9440cc7011e3f2f635852

This should do it:

if(preg_match('/[.?!]\h*$/', $string)){
      echo 'true';
} else {
     echo 'false';
}

This is a character class, [], allowing one of the characters inside. The $ is the end of the string. The \h* is any amount of horizontal whitespace after the symbol and before the end of the string. If you want new lines as well to be allowed use \s*.

Regex101 Demo: https://regex101.com/r/yS3fQ6/1

PHP Demo: https://eval.in/495500