$re = '/<span\b[^>]*+>(?# Открывающий span с любыми атребутами
)\s*+(?# Пробелы
)(?<number>\-?+\d++(?:[\.\,]\d++)?+)(?# Число
)\s*+(?# Пробелы
)<\/span>(?# Закрывающий span)/us';
$str = '<span class="company__segment__inner">0</span>
<span class="company__segment__inner">1</span>
<span class="company__segment__inner">1.</span>
<span class="company__segment__inner">1.0</span>
<span class="company__segment__inner">-1</span>
<span class="company__segment__inner">12121.12212</span>
<span class="company__segment__inner">192.168.0.1</span>
<span class="company__segment__inner">Только числа</span>
<span>1</span>
<spank>1</spank>
<span>-0,123</span>
<span>
-0,123
</span>';
$subst = "${number}";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php