stuck on a simple preg_replace with backreference

Question

Sorry guys, I got stuck on this:

$data_update = preg_replace($id.'(.*?)'.$s.PHP_EOL, $id.$1.$s.$text.PHP_EOL, $data_update, 1);

$id = '23423';
$s = '|';
$text = 'content to insert';

Basically what I am trying to do is match everything that's between $id and a PHP End of Line in a flat file text that has multiple lines and replace it with the same line that has some content inserted right before the end of line. And I have the "1" modifier at the end because I want this to happen ONLY on the line that matches that id.

What am I doing wrong?

Why use $s="|"? Please post the line example. Maybe you need preg_replace('/\b(' . $id . '\b.*)(\R)/', '$1 ' . $text . '$2', $data_update, 1);? See this PHP demo. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 3, 2020 at 21:46
@WiktorStribiżew I need to patch for EOL because the end of line has been inserted in the flat file text as PHP_EOL so you can think of my data variable as this: $data_update = "23423 in between some text".PHP_EOL; $data_update .= "00000 in between some more text".PHP_EOL; $data_update .= "11111 in between even more text".PHP_EOL; — marcnyc
– marcnyc, Commented May 3, 2020 at 23:49
If you need help, provide an MCVE (minimal complete verifiable example). — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 4, 2020 at 0:24
your example helped and that PHP demo was great for me to figure it out! thank you! @WiktorStribiżew — marcnyc
– marcnyc, Commented May 4, 2020 at 1:46

Wiktor Stribiżew · Accepted Answer · 2020-05-04 08:42:32Z

1

I suggest using

preg_replace('/\b(' . $id . '\b.*)(\R)/', '$1 ' . $text . '$2', $data_update, 1);

The pattern will look like \b(23423\b.*)(\R) and will match

\b - a word boundary
(23423\b.*) - Group 1: the ID as a whole word and then the rest of the line
(\R) - Group 2: any line break sequence

See full PHP demo:

$id = '23423';
$s = '|';
$text = 'content to insert';
$data_update = "Some text 23423 in between end\nsome text";
$data_update = preg_replace('/\b(' . $id . '\b.*)(\R)/', '$1 ' . $text . '$2', $data_update, 1);

Output:

Some text 23423 in between end content to insert
some text

answered May 4, 2020 at 8:42

Wiktor Stribiżew

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