PHP String Cleanup Functions

PHP provides functions that help to clean up strings by removing unwanted whitespace or other characters from the beginning and/or end of the string: trim, rtrim, and ltrim. PHP also provides another type of cleanup function: strip_tags, which removes HTML and PHP tags from strings.

Let's start with trim and related functions. The strip_tags function is described and demonstrated below.

Cleanup Beginning and End of Strings

PHP's trim function removes whitespace or other characters you specify from both the beginning and end of the string passed to it. The rtrim function removes these unwanted characters from the end of the string (right) while ltrim removes them from the beginning (left).

The trim, rtrim, and ltrim functions all accept two arguments: the string to clean up, and an optional list of characters to remove. If you don't specify a second argument, these functions will remove the following whitespace characters from the beginning and/or end of the string: spaces, tabs (\t), newlines (\n), carriage returns (\r), vertical tabs (\x0B), and NUL-byte characters (\0).

First we demonstrate the trim function with two example strings. In the first string, white space characters are entered literally, while the second uses escape sequences:

// whitespace entered via keyboard
$str = "    Dear Mr. Martin, 
";
var_dump( trim($str) ); // string(16) "Dear Mr. Martin," 

// whitespace using escape sequences
$str2 = "\tDear Mr. Martin,\n";
var_dump( trim($str2) ); // string(16) "Dear Mr. Martin," 

As the output of var_dump shows, the result of applying trim is the same for both strings. All the whitespace characters are removed from the beginning and end of the string.

Next we demonstrate the ltrim function, which just removes characters from the left, the beginning of the string. We apply ltrim to the strings from the example above:

// apply ltrim to both example strings
var_dump( ltrim($str) );
var_dump( ltrim($str2) );
// View Source display:
/*
string(17) "Dear Mr. Martin,
"
*/ 

The result is the same for both strings: the whitespace has been removed from the left but remains intact on the right.

We use var_dump to get an accurate view of the results of our trim functions. It gives us the length of the string and encloses it in quotes. Note that when viewed in the browser, line breaks and extra spaces that exist in the string cannot be seen. To see an accurate display of the string, view browser page source (Ctrl-U), or display the output inside <pre> tags. Find out more about using var_dump to display data.

Specifying Characters to Remove

As mentioned above, you can pass a second argument to trim and related functions to specify the characters to remove. In this example, we demonstrate using rtrim to remove a trailing comma:

// second argument specifies characters to trim from first
var_dump( rtrim('Hello,', ',') ); // string(5) "Hello" 

In the example below, our second argument specifies that we would like to remove spaces, tabs, and commas from the beginning and end of the string passed to the trim function:

// trim spaces, tabs, and commas 
var_dump( trim("\tHello, ", " \t,") ); // string(5) "Hello"

The output of var_dump shows that we have succeeded in removing the specified characters in both examples.

Remove Range of Characters

You can specify a range of characters in the second argument by using two dots between them. For example, to remove integers, specify a range using 0..9. In the following example, our string includes integers and spaces at the beginning and end of the string. We can use trim to remove them as follows:

// trim integers and spaces from left and right of string
var_dump( trim('12 Hello World 34', ' 0..9') ); // string(11) "Hello World" 

Strip HTML and PHP Tags

PHP's strip_tags function removes all HTML and PHP tags from the string passed to it. HTML attributes and values are removed, leaving only tag content. The following example demonstrates:

// example string with HTML markup
$str = <<<EOS
    <p class="txt">Some paragraph text here.</p>
    <script src="http://example.com/script.js"></script>
EOS;

// apply strip_tags to above string
$stripped = strip_tags($str);
var_dump($stripped);
// browser display (View Source shows more whitespace):
// string(34) " Some paragraph text here. " 

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