trim()

(PHP 4, PHP 5, PHP 7)

去除字符串首尾处的空白字符（或者其他字符）

说明

trim(string $str[,string $character_mask=" tnr0x0B"]): string

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：

""(ASCII32(0x20))，普通空格符。
"t"(ASCII9(0x09))，制表符。
"n"(ASCII10(0x0A))，换行符。
"r"(ASCII13(0x0D))，回车符。
"0"(ASCII0(0x00))，空字节符。
"x0B"(ASCII11(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 #1trim()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"

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
Becausetrim()trims characters from the beginning and end of astring, 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"whereastrim('abc','b')seemingly does not.

参见

ltrim() 删除字符串开头的空白字符（或其他字符）
rtrim() 删除字符串末端的空白字符（或者其他字符）
str_replace() 子字符串替换

It may be useful to know that trim() returns an empty string when the argument is an unset/null variable.

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
----------------------------

Non-breaking spaces can be troublesome with trim:
<?php
// turn some HTML with non-breaking spaces into a "normal" string
$myHTML = "&nbsp;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);
// &nbsp; 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!
?>

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;
}

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

It is worth mentioning that trim, ltrim and rtrim are NOT multi-byte safe, meaning that trying to remove an utf-8 encoded non-breaking space for instance will result in the destruction of utf-8 characters than contain parts of the utf-8 encoded non-breaking space, for instance:
non breaking-space is "\u{a0}" or "\xc2\xa0" in utf-8, "µ" is "\u{b5}" or "\xc2\xb5" in utf-8 and "à" is "\u{e0}" or "\xc3\xa0" in utf-8
$input = "\u{a0}µ déjà\u{a0}"; // " µ déjà "
$output = trim($input, "\u{a0}"); // "▒ déj▒" or whatever how the interpretation of broken utf-8 characters is performed
$output got both "\u{a0}" characters removed but also both "µ" and "à" characters destroyed

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.

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").]

Another way to trim all the elements of an array
<?php
$newarray = array_map('trim', $array);
?>

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;
}
?>

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 `"&nbsp;abà"`.

Beware with trimming apparently innocent characters. It is NOT a Unicode-safe function:
<?php
echo trim('≈ [Approximation sign]', '– [en-dash]'); //  [Approximation sig
?>
The en-dash here is breaking the Unicode characters.
And also prevents the open-square-bracket from being seen as part of the characters to trim on the left side, letting it untouched in the resulting string.

utf-8:
trim($text, " \t\n\r\0\x0B\xC2\xA0");

If you want to check whether something ONLY has whitespaces, use the following:
<?php
if (trim($foobar)=='') {
  echo 'The string $foobar only contains whitespace!';
}
?>

Simple Example I hope you will understand easily:
<?php
// Inserting empty variable;
$name = "";
if( !(empty( $name )) )
{
  $sql = "INSERT INTO `users`( name ) VALUE( '$name' );";
}
// But is not empty that will be inserted but space
$name2 = "   ";
if( !(empty( $name )) )
{
  $sql = "INSERT INTO `users`( name ) VALUE( '$name' );";
}
// Now that will not be inserted by using trim() function
$name3 = "   ";
if( !(empty( trim($name) )) )
{
  $sql = "INSERT INTO `users`( name ) VALUE( '$name' );";
}
?>

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");