Strings in PHP

Master string handling in PHP: single-quoted, double-quoted, heredoc, nowdoc, interpolation, indexing, traversal, searching, slicing, comparing, replacing, and common string functions.

Creating Strings

PHP has four ways to create strings: single quotes (`''`), double quotes (`""`), heredoc (`<<<LABEL`), and nowdoc (`<<<'LABEL'`). Each behaves differently regarding variable interpolation and escape sequences.

1. Single-quoted Strings

The simplest form — no interpolation, almost no escape sequences. What you type is literally what you get.

2. Double-quoted Strings

Support variable interpolation and all escape sequences — the most commonly used string style.

3. Heredoc (<<<LABEL)

A multiline string that behaves like a double-quoted string — supports interpolation and escape sequences.

4. Nowdoc (<<<'LABEL')

A multiline string that behaves like a single-quoted string — NO interpolation whatsoever.

String Basics (Indexing, Length, Traversal)

PHP strings are sequences of bytes. You can access individual characters by index, get the total length with `strlen()`, and traverse every character with a `for` loop or `str_split()`.

1. Accessing a Character at a Specific Index

Use `$str[index]` or `substr()` to access a character. Index starts from 0.

2. Getting String Length

`strlen()` returns the byte length. For multibyte (UTF-8) strings use `mb_strlen()`.

3. Traversing Through a String

Loop through each character using a `for` loop or `str_split()`.

String Interpolation

PHP supports several interpolation styles inside double-quoted strings and heredocs. Understanding all forms helps you write clean, readable output without messy concatenation.

1. Simple Variable Interpolation

PHP replaces `$varName` directly inside double-quoted strings.

2. Curly-brace Interpolation `{$var}`

Curly braces make the variable boundary explicit and allow array/property access inside strings.

3. Complex (Variable Variable) Interpolation `${expr}`

The `${expr}` form evaluates the expression inside braces as a variable name — useful for variable variables.

Comparing & Concatenating Strings

PHP uses the dot (`.`) operator for concatenation and provides `strcmp()`, `strcasecmp()`, and the spaceship operator for comparisons.

1. Concatenation with . and .=

The `.` operator joins two strings. `.=` appends to an existing variable.

2. Comparing Strings (Exact & Case-insensitive)

`strcmp()` for case-sensitive comparison, `strcasecmp()` for case-insensitive.

3. Repeating a String (str_repeat)

`str_repeat()` returns a string repeated a given number of times.

String Transformations

PHP provides a rich set of functions to transform string values — converting case, reversing, padding to a fixed width, and wrapping long text.

1. Case Conversion

`strtoupper()`, `strtolower()`, `ucfirst()`, `ucwords()` cover all common case needs.

2. Reversing a String (strrev)

`strrev()` returns the string in reverse character order.

3. Padding Strings (str_pad)

`str_pad()` pads a string to a given length — left, right, or both sides.

4. Wrapping Long Text (wordwrap)

`wordwrap()` breaks a string into lines of a given maximum width.

Slicing, Substrings, Splitting & Trimming

These operations are essential for parsing URLs, emails, CSV data, and user input.

1. substr() — Extract a Substring

`substr($str, $start, $length)` extracts a portion of the string.

2. explode() and implode() — Split & Join

`explode()` splits a string into an array; `implode()` joins an array into a string.

3. Trimming Whitespace (trim, ltrim, rtrim)

Remove leading and/or trailing whitespace or custom characters.

Searching & Replacing in Strings

PHP provides a complete toolkit for string searching — from simple `strpos()` to regex-based `preg_match()`. PHP 8.0 added `str_contains()`, `str_starts_with()`, and `str_ends_with()` for cleaner intent.

1. strpos() and strrpos() — Find Position

`strpos()` finds the first occurrence; `strrpos()` finds the last.

2. str_contains, str_starts_with, str_ends_with — PHP 8.0+

Clean, readable helpers that return `true`/`false` without the `!== false` pattern.

3. str_replace() and str_ireplace()

`str_replace()` replaces all occurrences of a substring. `str_ireplace()` is case-insensitive.

4. sprintf() and number_format()

Format values into strings with precise control over decimals, padding, and separators.

ASCII & Character Encoding

PHP provides `ord()` and `chr()` for converting between a character and its ASCII/Unicode code point.

1. ord() and chr() — Character ↔ Code

`ord()` returns the ASCII value of a character; `chr()` converts a code back to a character.