Remove a string from the beginning of a string
PhpStringPhp Problem Overview
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.
Php Solutions
Solution 1 - Php
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.
Solution 2 - Php
You can use regular expressions with the caret symbol (^
) which anchors the match to the beginning of the string:
$str = preg_replace('/^bla_/', '', $str);
Solution 3 - Php
function remove_prefix($text, $prefix) {
if(0 === strpos($text, $prefix))
$text = substr($text, strlen($prefix)).'';
return $text;
}
Solution 4 - Php
Here's an even faster approach:
// strpos is faster than an unnecessary substr() and is built just for that
if (strpos($str, $prefix) === 0) $str = substr($str, strlen($prefix));
Solution 5 - Php
Here.
$array = explode("_", $string);
if($array[0] == "bla") array_shift($array);
$string = implode("_", $array);
Solution 6 - Php
> 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
Solution 7 - Php
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.