PHP Substring Function (PHP substr)

The PHP substring function, substr, allows a programmer to retrieve a specified portion of a string known as a substring. String manipulation is a very important and sometimes tricky task so care must be taken to ensure that the functions are properly used and understood.

We usually need to use the PHP substring function anytime we want to break a larger string into a smaller string.

The tutorial below will show you how to properly use the PHP substring function and will help get you up to speed with PHP substrings.

PHP substr Syntax

The syntax of the PHP substring function, substr, is shown below:

$substring = substr($original, $start, $length)

Where $substring is the result after performing the function, $original is the original string, and:

Parameter	Description
$start	Required. Tells where to start in the original string. Zero - Starts at the beginning of the string A positive number - Starts at that character from the beginning of the string A negative number - Starts that many characters from the end of the string
$length	Optional. Tells the length of the substring to be returned. If no $length is specified, everything from the starting point to the end of the string will be returned. A positive number - The number of characters (starting at the start position) to be returned A negative number - That number of characters will be omitted from the end of the string

You do not need to memorize the boring syntax above immediately. Instead, look at our PHP substring examples below to see how it actually works.

PHP substring Example - Using positive parameters

Take a look at the following example. The comments in the code are a guide to what each substring instruction does:

<?php
 
// declare the string we will be breaking into substrings
$string = 'I love Tutorial Arena so much';
 
$result1 = substr($string, 2);  // from 2nd character to the end
$result2 = substr($string, 7);  // from 7th character to the end
 
// start at the 7th character and then be 8 characters long
$result3 = substr($string, 7, 8); 
 
echo $result1 . '<br />';
echo $result2 . '<br />';
echo $result3 . '<br />';
 
?>

The result:

love Tutorial Arena so much
Tutorial Arena so much
Tutorial

The examples above show how to use the PHP substring function with positive parameters only. Negative parameters are less frequently used but we look at them nonetheless below.

PHP Substring Example - Using negative parameters

The example below shows how to use the PHP substring function with negative parameters. Once again, the comments in the code are a guide to what each substring instruction does.

<?php
 
// declare the string we will be breaking into substrings
$string = 'abcdefg';
 
$result1 = substr($string, -3);  // start 3 characters from the end
$result2 = substr($string, -5);  // start 5 characters from the end
 
// start 5 characters from the end, then omit the last 2 characters
$result3 = substr($string, -5, -2);
 
echo $result1 . '<br />';
echo $result2 . '<br />';
echo $result3 . '<br />';
 
?>

The result will be:

efg
cdefg
cde

As you just saw in the example above, using the PHP substr function with negative parameters is not as hard as it would first seem. Just keep the syntax in mind a practice with a bit of code to confirm your understanding.

PHP Single character substring

If we want to retrieve only a single character from a string we do not even need to use substr in PHP. Take a look:

<?php
 
$string = 'I love Tutorial Arena so much';
 
echo substr($string, 7, 1); // start at 7th char and 1 char long
echo '<br />';
echo $string[7]; // return 7th character in string
 
?>

You will get:

T
T

If you are extracting only a single character, it saves you code if you treat the string as an array of characters and retrieve the character you want using its location in the string. Remember that a string in PHP is treated as an array of characters and that is why this is possible.

PHP Substring Function without the use of substr

As we just learnt above, we are able to extract a character from a string without the use of substr in PHP. This concept can be adapted quite easily to return a substring from a string without the use of the PHP substr function at all.

To do this, we would have to get what we want character by character. Have a look below:

<?php
 
$string = 'I love Tutorial Arena so much';
$start = 7; // where in the string to start
$length = 8; // how long our substring should be
$answer = ''; // variable used to hold our answer
 
// loop through string from $start to $length and get characters
for ($i = $start; $i < ($start + $length); $i++)
	$answer .= $string[$i];
 
echo $answer;
 
?>

The result:

Tutorial

As you can see, we actually iterated through our original string starting at the character we want, then pulling each character from the current location and appending it to the variable which holds our answer.

PHP Substring Function Tip

Remember that when working on strings (as with arrays), the first character is always counted as 0. This little rule is easy to forget as it may seem counter-intuitive to some.

We hope this PHP substr tutorial was helpful.

Citation: http://php.net/manual/en/function.substr.php