Replace substrings with an incremented counter value

Question

Basically what I\'m looking for is the PHP version of this thread: Find, replace, and increment at each occurence of string

I would like to replace the keyword follow

Answer 1

I prefer to use preg_replace_callback() for this task . It is a more direct solution than making iterated single preg_replace() calls which restart from the beginning of the string each time (checking text that has already been replaced).

• ^ means the start of a line because of the m pattern modifier.
• \K means restart the full string match. This effectively prevents the literal > from being replaced and so only the literal string num is replaced.
• the static counter declaration will only set $counter to 0 on the first visit.
• the custom function does not need to receive the matched substring because the entire full string match is to be replaced.

Code: (Demo)

$text = <<<TEXT
>num, blah, blah, blah

ATCGACTGAATCGA

>num, blah, blah, blah

ATCGATCGATCGATCG

>num, blah, blah, blah

ATCGATCGATCGATCG
TEXT;

echo preg_replace_callback(
         "~^>\Knum~m",
         function () {
             static $counter = 0;
             return ++$counter;
         },
         $text
     );

Answer 2

preg_replace(array_fill(0, 5, '/'.$findme.'/'), range(1, 5), $string, 1);

Example:

preg_replace(array_fill(0, 5, '/\?/'), range(1, 5), 'a b ? c ? d ? e f g ? h ?', 1);

Output

a b 1 c 2 d 3 e f g 4 h 5

Answer 3

$str = 'a hello a some a';
$i = 0;

while (strpos($str, 'a') !== false)
{
    $str = preg_replace('/a/', $i++, $str, 1);
}

echo $str;

Answer 4

Here's my two cents

function str_replace_once($correct, $wrong, $haystack) {
    $wrong_string = '/' . $wrong . '/';
    return preg_replace($wrong_string, $correct, $haystack, 1);
}

The above function is used to replace the string occurence only once, but you are free to edit the function to perform every other possible operation.

Answer 5

If I understood your question properly...

<?php
//data resides in data.txt
$file = file('data.txt');
//new data will be pushed into here.
$new = array();
//fill up the array
foreach($file as $fK =>$fV) $new[] = (substr($fV, 0, 1)==">")? str_replace("num", $fK/2, $fV) : $fV;
//optionally print it out in the browser.
echo "<pre>";
print_r($new);
echo "</pre>";
//optionally write to file...
$output = fopen("output.txt", 'w');
foreach($new as $n) fwrite($output, $n);
fclose($output);