Remove a string from the beginning of a string - php

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 found at the beginning of the string?
With str_replace(), it removes all bla_'s.

Answer 1

Plain form, without regex:
$prefix = 'bla_';
$str = 'bla_string_bla_bla_bla';
if (substr($str, 0, strlen($prefix)) == $prefix) {
$str = substr($str, strlen($prefix));
}
Takes: 0.0369 ms (0.000,036,954 seconds)
And with:
$prefix = 'bla_';
$str = 'bla_string_bla_bla_bla';
$str = preg_replace('/^' . preg_quote($prefix, '/') . '/', '', $str);
Takes: 0.1749 ms (0.000,174,999 seconds) the 1st run (compiling), and 0.0510 ms (0.000,051,021 seconds) after.
Profiled on my server, obviously.

Answer 2

You can use regular expressions with the caret symbol (^) which anchors the match to the beginning of the string:
$str = preg_replace('/^bla_/', '', $str);

Answer 3

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

Answer 4

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 5

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

Answer 6

In PHP 8+ we can simplify using the str_starts_with() function:
$str = "bla_string_bla_bla_bla";
$prefix = "bla_";
if (str_starts_with($str, $prefix)) {
$str = substr($str, strlen($prefix));
}
https://www.php.net/manual/en/function.str-starts-with.php
EDIT: Fixed a typo (closing bracket) in the example code.

Answer 7

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

Answer 8

Lots of different answers here. All seemingly based on string analysis. Here is my take on this using PHP explode to break up the string into an array of exactly two values and cleanly returning only the second value:
$str = "bla_string_bla_bla_bla";
$str_parts = explode('bla_', $str, 2);
$str_parts = array_filter($str_parts);
$final = array_shift($str_parts);
echo $final;
Output will be:
string_bla_bla_bla

Answer 9

Symfony users can install the string component and use trimPrefix()
u('file-image-0001.png')->trimPrefix('file-'); // 'image-0001.png'

Answer 10

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.