PHP str_replace

Question

I have the string $var in which I need to replace some text. The first \"X\" needs to be replaced by \"A\", the second \"X\" needs to be replaced by B and so on, here is an exam

Answer 1

You could use preg_replace_callback():

// as many as you think you'll need, maximum.
// this can be programmatically generated, if need be
$replacements = array('A', 'B', 'C', 'D', 'E', 'F', 'G'); // and so on    

function get_replace_value($matches) {
    global $replacements;
    return array_shift($replacements);
}

$var = preg_replace_callback("/" + preg_quote($needle) + "/",
    "get_replace_value", $var);

Answer 2

You could use preg_replace's limit argument to only replace once.

<?php
    $var = 'X X X X';
    $replace = array('A', 'B', 'C', 'D');
    foreach($replace as $r)
        $var = preg_replace('/X/', $r, $var, 1);
    echo $var;
?>

http://codepad.viper-7.com/ra9ulA

Answer 3

$var = 'X X X X';
$replacements = array('A', 'B', 'C', 'D');

$var = preg_replace_callback('/X/', function() use (&$replacements) {
    return array_shift($replacements);
}, $var);

---

Other solution:

$var = preg_replace('/X/', 'A', $var, 1);
$var = preg_replace('/X/', 'B', $var, 1);
$var = preg_replace('/X/', 'C', $var, 1);
$var = preg_replace('/X/', 'D', $var, 1);

This one uses the $limit parameter of preg_replace (we replace only one occurrence per call).

Answer 4

Lots of loops are happening in the other answers, here's an alternative.

$var = 'X X X X X X X';
$replace = array('A', 'B', 'C', 'D');
$var = preg_replace(array_fill(0, count($replace), '/X/'), $replace, $var, 1);
echo $var; // A B C D X X X

Answer 5

Without use of regex

$arr = explode('X', 'X X X X');
$rep = array('A','B','C','D');
foreach ($arr as $idx=>$val)
{
  $arr[$idx] = $val.$rep[$idx];
}
echo implode($arr);

Answer 6

Yet one more solution (more for a dynamic number of Xs):

<?php

  $foo = 'X X X X X X';

  $Xs = preg_match_all('/\bX\b/',$foo,$_); if ($Xs === false) $Xs = 0;
  $alphabet = range('A', chr(64 + $Xs));
  foreach ($alphabet as $letter){
    $foo = preg_replace('/\bX\b/', $letter, $foo, 1);
  }

  echo $foo;

I also added the \b in to the pattern to only replace Xs that are free-standing, so "FAUX PAS X" only replaces the last X.

demo

alphabet_replace (more modular form)