使用strpos和substr:

<?php

$longString = "I have a code snippet written in PHP that pulls a block of text.";
$truncated = substr($longString,0,strpos($longString,' ',30));

echo $truncated;

这将为您提供一个在30个字符后的第一个空格处截断的字符串。

好吧，所以我得到了另一个版本的这个基于上面的答案，但考虑到更多的东西(utf-8， \n和 )，如果与wp一起使用，也是剥离wordpress shortcodes注释的行。

function neatest_trim($content, $chars) 
  if (strlen($content) > $chars) 
  {
    $content = str_replace(' ', ' ', $content);
    $content = str_replace("\n", '', $content);
    // use with wordpress    
    //$content = strip_tags(strip_shortcodes(trim($content)));
    $content = strip_tags(trim($content));
    $content = preg_replace('/\s+?(\S+)?$/', '', mb_substr($content, 0, $chars));

    $content = trim($content) . '...';
    return $content;
  }

我创建了一个更类似于substr的函数，并使用了@Dave的思想。

function substr_full_word($str, $start, $end){
    $pos_ini = ($start == 0) ? $start : stripos(substr($str, $start, $end), ' ') + $start;
    if(strlen($str) > $end){ $pos_end = strrpos(substr($str, 0, ($end + 1)), ' '); } // IF STRING SIZE IS LESSER THAN END
    if(empty($pos_end)){ $pos_end = $end; } // FALLBACK
    return substr($str, $pos_ini, $pos_end);
}

注:全长切割可能小于substr。

通过使用wordwrap函数。它将文本分割成多行，这样最大宽度就是您指定的宽度，在单词边界处断开。分割之后，你只需取第一行:

substr($string, 0, strpos(wordwrap($string, $your_desired_width), "\n"));

这个线性程序不能处理的一件事是，当文本本身比所需的宽度短时。为了处理这种边情况，我们应该这样做:

if (strlen($string) > $your_desired_width) 
{
    $string = wordwrap($string, $your_desired_width);
    $string = substr($string, 0, strpos($string, "\n"));
}

上面的解决方案存在一个问题，即如果文本在实际切点之前包含换行符，则会过早地切割文本。这里有一个解决这个问题的版本:

function tokenTruncate($string, $your_desired_width) {
  $parts = preg_split('/([\s\n\r]+)/', $string, null, PREG_SPLIT_DELIM_CAPTURE);
  $parts_count = count($parts);

  $length = 0;
  $last_part = 0;
  for (; $last_part < $parts_count; ++$last_part) {
    $length += strlen($parts[$last_part]);
    if ($length > $your_desired_width) { break; }
  }

  return implode(array_slice($parts, 0, $last_part));
}

另外，这里是用于测试实现的PHPUnit测试类:

class TokenTruncateTest extends PHPUnit_Framework_TestCase {
  public function testBasic() {
    $this->assertEquals("1 3 5 7 9 ",
      tokenTruncate("1 3 5 7 9 11 14", 10));
  }

  public function testEmptyString() {
    $this->assertEquals("",
      tokenTruncate("", 10));
  }

  public function testShortString() {
    $this->assertEquals("1 3",
      tokenTruncate("1 3", 10));
  }

  public function testStringTooLong() {
    $this->assertEquals("",
      tokenTruncate("toooooooooooolooooong", 10));
  }

  public function testContainingNewline() {
    $this->assertEquals("1 3\n5 7 9 ",
      tokenTruncate("1 3\n5 7 9 11 14", 10));
  }
}

编辑:

像'à'这样的特殊UTF8字符不会被处理。在REGEX的末尾添加'u'来处理它:

部分美元= preg_split (' / ([\ s \ n \ r] +) / u ',美元字符串,null, PREG_SPLIT_DELIM_CAPTURE);

使用strpos和substr:

<?php

$longString = "I have a code snippet written in PHP that pulls a block of text.";
$truncated = substr($longString,0,strpos($longString,' ',30));

echo $truncated;

这将为您提供一个在30个字符后的第一个空格处截断的字符串。

就我所知，这里所有的解只有在起点固定的情况下才有效。 允许你转动这个: 悲伤之神，神圣之神，痛苦之神，痛苦之神。Ut enim ad minim veniam。 到这个: 神圣的，神圣的… 如果想要截断一组特定关键字周围的单词，该怎么办?

截断一组特定关键字周围的文本。

我们的目标是能够转换这个:

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna liqua. Ut enim ad minim veniam.

到这个:

...consectetur adipisicing elit, sed do eiusmod tempor...

这是在显示搜索结果、摘要等时非常常见的情况。为了实现这一点，我们可以结合使用以下两种方法:

    /**
     * Return the index of the $haystack matching $needle,
     * or NULL if there is no match.
     *
     * This function is case-insensitive  
     * 
     * @param string $needle
     * @param array $haystack
     * @return false|int
     */
    function regexFindInArray(string $needle, array $haystack): ?int
    {
        for ($i = 0; $i < count($haystack); $i++) {
            if (preg_match('/' . preg_quote($needle) . '/i', $haystack[$i]) === 1) {
                return $i;
            }
        }
        return null;
    }

    /**
     * If the keyword is not present, it returns the maximum number of full 
     * words that the max number of characters provided by $maxLength allow,
     * starting from the left.
     *
     * If the keyword is present, it adds words to both sides of the keyword
     * keeping a balanace between the length of the suffix and the prefix.
     *
     * @param string $text
     * @param string $keyword
     * @param int $maxLength
     * @param string $ellipsis
     * @return string
     */
    function truncateWordSurroundingsByLength(string $text, string $keyword, 
            int $maxLength, string $ellipsis): string
    {
        if (strlen($text) < $maxLength) {
            return $text;
        }

        $pattern = '/' . '^(.*?)\s' .
                   '([^\s]*' . preg_quote($keyword) . '[^\s]*)' .
                   '\s(.*)$' . '/i';
        preg_match($pattern, $text, $matches);

        // break everything into words except the matching keywords, 
        // which can contain spaces
        if (count($matches) == 4) {
            $words = preg_split("/\s+/", $matches[1], -1, PREG_SPLIT_NO_EMPTY);
            $words[] = $matches[2];
            $words = array_merge($words, 
                              preg_split("/\s+/", $matches[3], -1, PREG_SPLIT_NO_EMPTY));
        } else {
            $words = preg_split("/\s+/", $text, -1, PREG_SPLIT_NO_EMPTY);
        }

        // find the index of the matching word
        $firstMatchingWordIndex = regexFindInArray($keyword, $words) ?? 0;

        $length = false;
        $prefixLength = $suffixLength = 0;
        $prefixIndex = $firstMatchingWordIndex - 1;
        $suffixIndex = $firstMatchingWordIndex + 1;

        // Initialize the text with the matching word
        $text = $words[$firstMatchingWordIndex];

        while (($prefixIndex >= 0 or $suffixIndex <= count($words))
                and strlen($text) < $maxLength and strlen($text) !== $length) {
            $length = strlen($text);
            if (isset($words[$prefixIndex])
                and (strlen($text) + strlen($words[$prefixIndex]) <= $maxLength)
                and ($prefixLength <= $suffixLength 
                     or strlen($text) + strlen($words[$suffixIndex]) <= $maxLength)) {
                $prefixLength += strlen($words[$prefixIndex]);
                $text = $words[$prefixIndex] . ' ' . $text;
                $prefixIndex--;
            }
            if (isset($words[$suffixIndex])
                and (strlen($text) + strlen($words[$suffixIndex]) <= $maxLength)
                and ($suffixLength <= $prefixLength 
                     or strlen($text) + strlen($words[$prefixIndex]) <= $maxLength)) {
                $suffixLength += strlen($words[$suffixIndex]);
                $text = $text . ' ' . $words[$suffixIndex];
                $suffixIndex++;
            }
        }

        if ($prefixIndex > 0) {
            $text = $ellipsis . ' ' . $text;
        }
        if ($suffixIndex < count($words)) {
            $text = $text . ' ' . $ellipsis;
        }

        return $text;
    }

现在你可以做:

$text = 'Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do' .
        'iusmod tempor incididunt ut labore et dolore magna liqua. Ut enim' .
        'ad minim veniam.';

$text = truncateWordSurroundingsByLength($text, 'elit', 25, '...');

var_dump($text); // string(32) "... adipisicing elit, sed do ..."

运行代码。