[php] Remove a string from the beginning of a string

I have a string that looks like this:

$str = "bla_string_bla_bla_bla";

How can I remove the first bla_; but only if it's found at the beginning of the string?

With str_replace(), it removes all bla_'s.

You can use regular expressions with the caret symbol (^) which anchors the match to the beginning of the string:

$str = preg_replace('/^bla_/', '', $str);

function remove_prefix($text, $prefix) {
    if(0 === strpos($text, $prefix))
        $text = substr($text, strlen($prefix)).'';
    return $text;
}

Here's an even faster approach:

// strpos is faster than an unnecessary substr() and is built just for that 
if (strpos($str, $prefix) === 0) $str = substr($str, strlen($prefix));

Here.

$array = explode("_", $string);
if($array[0] == "bla") array_shift($array);
$string = implode("_", $array);

Nice speed, but this is hard-coded to depend on the needle ending with _. Is there a general version? – toddmo Jun 29 at 23:26

A general version:

$parts = explode($start, $full, 2);
if ($parts[0] === '') {
    $end = $parts[1];
} else {
    $fail = true;
}

Some benchmarks:

<?php

$iters = 100000;
$start = "/aaaaaaa/bbbbbbbbbb";
$full = "/aaaaaaa/bbbbbbbbbb/cccccccccc/dddddddddd/eeeeeeeeee";
$end = '';

$fail = false;

$t0 = microtime(true);
for ($i = 0; $i < $iters; $i++) {
    if (strpos($full, $start) === 0) {
        $end = substr($full, strlen($start));
    } else {
        $fail = true;
    }
}
$t = microtime(true) - $t0;
printf("%16s : %f s\n", "strpos+strlen", $t);

$t0 = microtime(true);
for ($i = 0; $i < $iters; $i++) {
    $parts = explode($start, $full, 2);
    if ($parts[0] === '') {
        $end = $parts[1];
    } else {
        $fail = true;
    }
}
$t = microtime(true) - $t0;
printf("%16s : %f s\n", "explode", $t);

On my quite old home PC:

$ php bench.php

Outputs:

   strpos+strlen : 0.158388 s
         explode : 0.126772 s

Remove www. from beginning of string, this is the easiest way (ltrim)

$a="www.google.com";
echo ltrim($a, "www.");

<?php
$str = 'bla_string_bla_bla_bla';
echo preg_replace('/bla_/', '', $str, 1); 
?>

str_replace ( mixed $search , mixed $replace , mixed $subject [, int &$count ] )

now does what you want.

$str = "bla_string_bla_bla_bla";
str_replace("bla_","",$str,1);

I think substr_replace does what you want, where you can limit your replace to part of your string: http://nl3.php.net/manual/en/function.substr-replace.php (This will enable you to only look at the beginning of the string.)

You could use the count parameter of str_replace ( http://nl3.php.net/manual/en/function.str-replace.php ), this will allow you to limit the number of replacements, starting from the left, but it will not enforce it to be at the beginning.

This will remove first match wherever it is found i.e., start or middle or end.

$str = substr($str, 0, strpos($str, $prefix)).substr($str, strpos($str, $prefix)+strlen($prefix));