Remove a string from the beginning of a string

Question

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 fo

Answer 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);

Answer 2

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));

Answer 3

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/ffffdffffdffffdd/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

Answer 4

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

Answer 5

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

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

Answer 6

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

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