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PHP Expressions

Introduction to PHP Expressions

In PHP, almost everything you write is an expression. The simplest definition of an expression is “anything that has a value.” PHP expressions are the basic building blocks of any script. They can include constants, variables, functions, and even complex calculations.

Basic Forms of Expressions

The most common expressions in PHP are:

  • Constants like 5, “Hello”, true

  • Variables like $x, $name, $count

Example

$a = 5;

Here, 5 is an expression with the value 5. $a is also treated as an expression after assignment.

Expressions with Variables and Functions

Variables can store values from other expressions. Functions also return values that act as expressions.

Example

$b = $a;           // $b becomes 5
$c = strlen("PHP"); // strlen() returns 3, so $c becomes 3

Here, $a and strlen("PHP") are both expressions.

Operator-Assignment Expressions

When we assign a value using =, that assignment itself becomes an expression with the value being assigned.

Example

$a = 5;      // Expression that returns 5
$b = ($a = 10); // Both $a and $b become 10

Increment and Decrement Operators

These operators increase or decrease the value of a variable and also return a value.

  • ++$a (Pre-increment)

  • $a++ (Post-increment)

  • --$a (Pre-decrement)

  • $a-- (Post-decrement)

Example

$a = 5;
$b = ++$a;  // $b is 6, $a is 6
$c = $a--;  // $c is 6, $a becomes 5

Types of Expressions

PHP supports various types of expressions:

  • Arithmetic expressions
    5 + 3, $a * $b

  • Logical expressions
    $a && $b, !$a

  • Bitwise expressions
    $a & $b, $a | $b

  • Relational expressions
    $a == $b, $a > $b

  • Parentheses expressions
    (5 + 3) * 2

  • Explicit type conversion
    (int)$value, (string)$number

Regular Expressions in PHP

Regular expressions are special string patterns used for searching, matching, and replacing text. They are built with delimiters, pattern rules, and modifiers.

PHP supports:

  • POSIX regular expressions

  • Perl-compatible regular expressions (PCRE)

The most commonly used functions for regular expressions in PHP are:

  • preg_match() – checks if a pattern exists in a string

  • preg_replace() – replaces text based on pattern

  • preg_split() – splits a string using pattern

POSIX Regular Expressions

POSIX expressions are older but still useful. They work with character ranges and pattern quantifiers.

Brackets (Character Ranges)

Example

  • [0-9] – any digit

  • [a-z] – any lowercase letter

  • [A-Z] – any uppercase letter

  • [^a-zA-Z] – any character that is NOT a letter

Quantifiers

Examples

  • p+ – one or more occurrences of “p”

  • p* – zero or more “p”

  • p? – zero or one “p”

  • p{2} – exactly two “p”

  • ^p – starts with “p”

  • p$ – ends with “p”

Matching Examples

Examples

  • p.p – matches “pop”, “pip”

  • ^.{2}$ – matches any two-character string

  • <b>(.*)</b> – matches content inside <b> and </b>

  • p(hp)* – matches “p”, “php”, “phphp”, etc.

Predefined Character Classes

Examples

  • [[:alpha:]] – any alphabet letter

  • [[:digit:]] – any digit

  • [[:alnum:]] – alphanumeric (letters and numbers)

  • [[:space:]] – any whitespace (space, tab, newline)

Advantages and Uses of Regular Expressions

Regular expressions are used to:

  • Validate input (like email, phone number)

  • Search patterns in text

  • Replace or reformat text data

  • Split strings intelligently

They are powerful and efficient for handling complex text operations in web development.

Conclusion

PHP expressions are everywhere in your code. From simple constants to complex function calls and regular expressions, everything that returns a value is an expression. Regular expressions, in particular, allow powerful pattern-based string manipulation and are very useful for tasks like form validation, text search, and replacements.

Mastering expressions is essential to becoming an expert PHP developer.

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