It may be useful to know that trim() returns an empty string when the argument is an unset/null variable.
trim
(PHP 4, PHP 5, PHP 7)
trim — 去除字符串首尾处的空白字符（或者其他字符）
说明
string trim
( string
$str
[, string $character_mask = " \t\n\r\0\x0B"
] )
此函数返回字符串 str 去除首尾空白字符后的结果。如果不指定第二个参数，trim() 将去除这些字符：
- " " (ASCII 32 (0x20))，普通空格符。
- "\t" (ASCII 9 (0x09))，制表符。
- "\n" (ASCII 10 (0x0A))，换行符。
- "\r" (ASCII 13 (0x0D))，回车符。
- "\0" (ASCII 0 (0x00))，空字节符。
- "\x0B" (ASCII 11 (0x0B))，垂直制表符。
参数
-
str -
待处理的字符串。
-
character_mask -
可选参数，过滤字符也可由
character_mask参数指定。一般要列出所有希望过滤的字符，也可以使用 “..” 列出一个字符范围。
返回值
过滤后的字符串。
范例
Example #1 trim() 使用范例
<?php
$text = "\t\tThese are a few words :) ... ";
$binary = "\x09Example string\x0A";
$hello = "Hello World";
var_dump($text, $binary, $hello);
print "\n";
$trimmed = trim($text);
var_dump($trimmed);
$trimmed = trim($text, " \t.");
var_dump($trimmed);
$trimmed = trim($hello, "Hdle");
var_dump($trimmed);
// 清除 $binary 首位的 ASCII 控制字符
// （包括 0-31）
$clean = trim($binary, "\x00..\x1F");
var_dump($clean);
?>
以上例程会输出：
string(32) " These are a few words :) ... " string(16) " Example string " string(11) "Hello World" string(28) "These are a few words :) ..." string(24) "These are a few words :)" string(5) "o Wor" string(14) "Example string"
Example #2 使用 trim() 清理数组值
<?php
function trim_value(&$value)
{
$value = trim($value);
}
$fruit = array('apple','banana ', ' cranberry ');
var_dump($fruit);
array_walk($fruit, 'trim_value');
var_dump($fruit);
?>
以上例程会输出：
array(3) {
[0]=>
string(5) "apple"
[1]=>
string(7) "banana "
[2]=>
string(11) " cranberry "
}
array(3) {
[0]=>
string(5) "apple"
[1]=>
string(6) "banana"
[2]=>
string(9) "cranberry"
}
注释
Note: Possible gotcha: removing middle characters
Because trim() trims characters from the beginning and end of a string, it may be confusing when characters are (or are not) removed from the middle. trim('abc', 'bad') removes both 'a' and 'b' because it trims 'a' thus moving 'b' to the beginning to also be trimmed. So, this is why it "works" whereas trim('abc', 'b') seemingly does not.
add a note
User Contributed Notes 12 notes
Piopier ¶
11 years ago
ludko2 at gmail dot com ¶
7 years ago
Non-breaking spaces can be troublesome with trim:
<?php
// turn some HTML with non-breaking spaces into a "normal" string
$myHTML = " abc";
$converted = strtr($myHTML, array_flip(get_html_translation_table(HTML_ENTITIES, ENT_QUOTES)));
// this WILL NOT work as expected
// $converted will still appear as " abc" in view source
// (but not in od -x)
$converted = trim($converted);
// are translated to 0xA0, so use:
$converted = trim($converted, "\xA0"); // <- THIS DOES NOT WORK
// EDITED>>
// UTF encodes it as chr(0xC2).chr(0xA0)
$converted = trim($converted,chr(0xC2).chr(0xA0)); // should work
// PS: Thanks to John for saving my sanity!
?>
jubi at irc dot pl ¶
14 years ago
To remove multiple occurences of whitespace characters in a string an convert them all into single spaces, use this:
<?
$text = preg_replace('/\s+/', ' ', $text);
?>
------------
JUBI
http://www.jubi.buum.pl
tongcheong77 at gmail dot com ¶
10 months ago
if you are using trim and you still can't remove the whitespace then check if your closing tag inside the html document is NOT at the next line.
<textarea class="form-control" rows="5"><?php echo trim($comment);?></textarea>
there should be no spaces at the beginning and end of your echo statement, else trim will not work as expected.
aalhad at NOSPAM dot gmail dot com ¶
4 months ago
When specifying the character mask,
make sure that you use double quotes
<?php
$hello = "
Hello World "; //here is a string with some trailing and leading whitespace
$trimmed_correct = trim($hello, " \t\n\r"); //<--------OKAY
$trimmed_incorrect = trim($hello, ' \t\n\r'); //<--------NOT AS EXPECTED
print("----------------------------");
print("TRIMMED OK:".PHP_EOL);
print_r($trimmed_correct.PHP_EOL);
print("----------------------------");
print("TRIMMING NOT OK:".PHP_EOL);
print_r($trimmed_incorrect.PHP_EOL);
print("----------------------------".PHP_EOL);
?>
Here is the output:
----------------------------TRIMMED OK:
Hello World
----------------------------TRIMMING NOT OK:
Hello World
----------------------------
Hayley Watson ¶
13 years ago
Another way to trim all the elements of an array
<?php
$newarray = array_map('trim', $array);
?>
ivijan dot stefan at gmail dot com ¶
10 months ago
Standard trim() functions can be a problematic when come HTML entities. That's why i wrote "Super Trim" function what is used to handle with this problem and also you can choose is trimming from the begin, end or booth side of string.
<?php
function strim($str,$charlist=" ",$option=0){
if(is_string($str))
{
// Translate HTML entities
$return = strtr($str, array_flip(get_html_translation_table(HTML_ENTITIES, ENT_QUOTES)));
// Remove multi whitespace
$return = preg_replace("@\s+\s@Ui"," ",$return);
// Choose trim option
switch($option)
{
// Strip whitespace (and other characters) from the begin and end of string
default:
case 0:
$return = trim($return,$charlist);
break;
// Strip whitespace (and other characters) from the begin of string
case 1:
$return = ltrim($return,$charlist);
break;
// Strip whitespace (and other characters) from the end of string
case 2:
$return = rtrim($return,$charlist);
break;
}
}
return $return;
}
?>
Anonymous ¶
11 months ago
The comment of "ludko2 at gmail dot com" for trimming non-breaking spaces is wrong due the the way UTF-8 works. For example, it breaks on `" abà"`.
johovich at yandex dot ru ¶
9 months ago
trim is the fastest way to remove first and last char.
Benchmark comparsion 4 different ways to trim string with '/'
4 functions with the same result - array exploded by '/'
<?php
$s = '/catalog/lyustry/svet/dom-i-svet/';
$times = 100000;
print cycle("str_preg('$s');", $times);
print cycle("str_preg2('$s');", $times);
print cycle("str_sub_replace('$s');", $times);
print cycle("str_trim('$s');", $times);
print cycle("str_clear('$s');", $times);
//print_r(str_preg2($s));
function cycle($function, $times){
$count = 0;
if($times < 1){
return false;
}
$start = microtime(true);
while($times > $count){
eval($function);
$count++;
}
$end = microtime(true) - $start;
return "\n $function exec time: $end";
}
function str_clear($s){
$s = explode('/', $s);
$s = array_filter($s, function ($s){if(!empty($s)) return true;});
return $s;
}
function str_preg2($s){
$s = preg_replace('/((?<!.)\/(?=.))?((?<=.)\/(?!.))?/i', '', $s);
$s = explode('/', $s);
return $s;
}
function str_preg($s){
$s = preg_replace('/^(\/?)(.*?)(\/?)$/i', '$2', $s);
$s = explode('/', $s);
return $s;
}
function str_sub_replace($s){
$s = str_replace('/' , '' , mb_substr( $s , 0, 1)) . mb_substr( $s , 1, -1) . str_replace('/', '', mb_substr( $s , -1));
$s = explode('/', $s);
return $s;
}
function str_trim($s){
$s = trim($s, '/');
$s = explode('/', $s);
return $s;
}
jianglong at qiyi dot com ¶
3 years ago
Trim full width space will return mess character, when target string starts with '《'
@example
echo trim("《", " ");
@return
�
php version 5.4.27
[EDIT by cmb AT php DOT net: it is not necessarily safe to use trim with multibyte character encodings. The given example is equivalent to echo trim("\xe3\80\8a", "\xe3\x80\x80").]
dmr37 at cornell dot edu ¶
13 years ago
If you want to check whether something ONLY has whitespaces, use the following:
<?php
if (trim($foobar)=='') {
echo 'The string $foobar only contains whitespace!';
}
?>
HW ¶
14 years ago
You can combine character ranges and individual characters in trim()'s second argument (ditto for ltrim and rtrim). All of the specified characters and ranges will be used concurrently (i.e., if a character on either end of the string matches any of the specified charaters or character ranges, it will be trimmed). The characters and character ranges can be in any order (except of course that the character ranges need to be specified in increasing order) and may overlap.
E.g., trim any nongraphical non-ASCII character:
trim($text,"\x7f..\xff\x0..\x1f");
