php 从字符串的开头删除字符串
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Remove a string from the beginning of a string
提问by Alex
I have a string that looks like this:
我有一个看起来像这样的字符串：
$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?
我怎样才能删除第一个bla_；但前提是它位于字符串的开头？
With str_replace(), it removes allbla_'s.
使用str_replace()，它会删除所有bla_的。
回答by Fabio Mora
Plain form, without regex:
普通形式，没有正则表达式：
$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)
耗时：0.0369 毫秒（0.000,036,954 秒）
And with:
与：
$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.
注意到：0.1749毫秒（0.000,174,999秒）第一次运行（编译），和0.0510毫秒（0.000,051,021秒）之后。
Profiled on my server, obviously.
显然，在我的服务器上进行了分析。
回答by Tatu Ulmanen
You can use regular expressions with the caret symbol (^) which anchors the match to the beginning of the string:
您可以使用带有插入符号 ( ^) 的正则表达式，它将匹配锚定到字符串的开头：
$str = preg_replace('/^bla_/', '', $str);
回答by Pavel
function remove_prefix($text, $prefix) {
if(0 === strpos($text, $prefix))
$text = substr($text, strlen($prefix)).'';
return $text;
}
回答by cbrandolino
Here.
这里。
$array = explode("_", $string);
if($array[0] == "bla") array_shift($array);
$string = implode("_", $array);
回答by Aleksandar Bosakov
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
速度不错，但这是硬编码的，取决于以 _ 结尾的针。有通用版吗？– toddmo 6 月 29 日 23:26
A general version:
一般版本：
$parts = explode($start, $full, 2);
if ($parts[0] === '') {
$end = $parts[1];
} else {
$fail = true;
}
Some benchmarks:
一些基准：
<?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:
在我相当旧的家用电脑上：
$ php bench.php
Outputs:
输出：
strpos+strlen : 0.158388 s
explode : 0.126772 s
回答by Stefan Gabos
Here's an even faster approach:
这是一个更快的方法：
// strpos is faster than an unnecessary substr() and is built just for that
if (strpos($str, $prefix) === 0) $str = substr($str, strlen($prefix));
回答by Muzaffar Mahmood
This will remove first match wherever it is found i.e., start or middle or end.
这将删除找到的第一个匹配项，即开始或中间或结束。
$str = substr($str, 0, strpos($str, $prefix)).substr($str, strpos($str, $prefix)+strlen($prefix));
回答by Inca
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.)
我认为 substr_replace 可以满足您的需求，您可以将替换限制为字符串的一部分：http: //nl3.php.net/manual/en/function.substr-replace.php（这将使您只能查看字符串的开头。）
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.
您可以使用 str_replace ( http://nl3.php.net/manual/en/function.str-replace.php)的 count 参数，这将允许您限制替换次数，从左侧开始，但它不会强制它在开头。
回答by Bhanu Prakash Pandey
<?php
$str = 'bla_string_bla_bla_bla';
echo preg_replace('/bla_/', '', $str, 1);
?>
回答by Bog
str_replace ( mixed $search , mixed $replace , mixed $subject [, int &$count ] )
str_replace ( mixed $search , mixed $replace , mixed $subject [, int &$count ] )
now does what you want.
现在做你想做的。
$str = "bla_string_bla_bla_bla";
str_replace("bla_","",$str,1);
