The abs() function is an inbuilt function in PHP which is used to return the absolute (positive) value of a number. The abs() function in PHP is identical to what we call modulus in mathematics. The modulus or absolute value of a negative number is positive.
Syntax:
number abs( value )
Parameters: The abs() function accepts single parameter value which holds the number whose absolute value you want to find.
Return Value: It returns the absolute value of the number passed to it as argument.
Examples:
Input : abs(6) Output : 6 Input : abs(-6) Output : 6 Input : abs(6.4) Output : 6.4 Input : abs(-6.4) Output : 6.4
Below programs illustrate the abs() function in PHP:
Program 1: When a positive number is passed as a parameter:
<?php  echo (abs(6);   ?>      |
Output:
6
Program 2: When a negative number is passed as a parameter:
<?php  echo (abs(-6);   ?> |
Output:
6
Program 3: When a positive number with decimal places is passed as a parameter:
<?php  echo (abs(6.4);   ?>      |
Output:
6.4
Program 4: When a negative number with decimal places is passed as a parameter:
<?php  echo (abs(-6.4);   ?>      |
Output:
6.4
Reference: http://php.net/manual/en/function.abs.php
