替换某个行号的字符串

Question

I have a big piece of text, and i know at what line number a specific piece of string occurs. I need to replace that with something else. But how can i replace a certain string only at a certain line number?

Example text:

1: Lorem ipsum dolor sit amet, [[consectetur]] adipiscing elit. Aliquam 
2: imperdiet dolor ut urna hendrerit tempus in sit amet nibh. Maecenas 
3: est est, imperdiet quis tristique pulvinar, convallis et justo. 
4:
5: Duis nulla lacus, [[aliquet]] at ornare nec, ultricies ac erat. Aliquam 
6: dignissim, tellus et pharetra [[rhoncus]], magna nisi scelerisque urna, in 
7: imperdiet [[metus]] orci id risus. 

In this case, i only want to replace the [[ characters at line 1 and at line 6 with -- (two dashes).

Is there an easy of doing this in PHP?

Answer 1

There's no compact way for PHP, but you can read the file line by line and replace the string, where needed:

$f = fopen('example.txt', 'r');
for ($i = 1; ($line = fgets($f)) !== false; $i++) {
    if ($i == 1 || $i == 6)
        $line = str_replace('[[', '--', $line);

    echo $line;
}

fclose($f);