preg_match_ALL 的简单模式可以正常工作吗？ 如何与 preg_replace 一起使用？

Question

thanks by your help.

my target is use preg_replace + pattern for remove very sample strings.

then only using preg_replace in this string or others, I need remove ANY content into <tag and next symbol > , the pattern is so simple, then:

$x = '@<\w+(\s+[^>]*)>@is';
$s = 'DATA<td class="td1">111</td><td class="td2">222</td>DATA';
preg_match_all($x, $s, $Q);
print_r($Q[1]);

[1] => Array
    (
        [0] =>  class="td1"
        [1] =>  class="td2"
    )

work greath!

now I try remove strings using the same pattern:

$new_string = '';
$Q = preg_replace($x, "\\1$new_string", $s);
print_r($Q);

result is completely different.

what is bad in my use of preg_replace ?

using only preg_replace() how I can remove this strings?

(we can use foreach(...) for remove each string, but where is the error in my code?)

my result expected when I intro this value:

$s = 'DATA<td class="td1">111</td><td class="td2">222</td>DATA';

is this output:

$Q = 'DATA<td>111</td><td>222</td>DATA';

Answer 1

Let's break down your RegEx, @<\w+(\s+[^>]*)>@is , and see if that helps.

@          // Start delimiter
<          // Literal `<` character
\w+        // One or more word-characters, a-z, A-Z, 0-9 or _
(          // Start capturing group
  \s+      // One or more spaces
  [^>]*    // Zero or more characters that are not the literal `>`
)          // End capturing group
>          // Literal `>` character
@          // End delimiter
is         // Ignore case and `.` matches all characters including newline

Given the input DATA<td class="td1">DATA this matches <td class="td1"> and captures class="td1" . The difference between match and capture is very important.

When you use preg_match you'll see the entire match at index 0 , and any subsequent captures at incrementing indexes.

When you use preg_replace the entire match will be replaced. You can use the captures , if you so choose, but you are replacing the match .

I'm going to say that again: whatever you pass as the replacement string will replace the entirety of the found match . If you say $1 or \\=1 , you are saying replace the entire match with just the capture.

Going back to the sample after the breakdown, using $1 is the equivalent of calling:

str_replace('<td class="td1">', ' class="td1"', $string);

which you can see here: https://3v4l.org/ZkPFb

To your question "how to change [0] by $new_string ", you are doing it correctly, it is your RegEx itself that is wrong. To do what you are trying to do, your pattern must capture the tag itself so that you can say "replace the HTML tag with all of the attributes with just the tag".

As one of my comments noted, this is where you'd invert the capturing. You aren't interesting in capturing the attributes, you are throwing those away. Instead, you are interested in capturing the tag itself:

$string = 'DATA<td class="td1">DATA';
$pattern = '@<(\w+)\s+[^>]*>@is';

echo preg_replace($pattern, '<$1>', $string);

Demo: https://3v4l.org/oIW7d