80+ Essential PHP String Functions Every Web Developer Should Know

Strings form the foundation of the web. Whether it‘s HTML markup, URL parameters, form input, database content, or API responses, much of the data that powers websites and web applications comes in the form of strings.

PHP provides an extensive set of built-in functions for inspecting, searching, splitting, combining, encoding, translating, and manipulating strings. Mastering PHP‘s string handling capabilities is essential for any PHP developer building modern web software.

In this guide, we‘ll tour over 80 key string functions in PHP. While not an exhaustive list, we‘ll cover the core string functions that underpin most common use cases.

Let‘s dive in by looking at some fundamental string functions for determining length, searching, and extracting substrings.

Inspecting and Searching Strings

At the heart of string handling is the ability to examine the contents and structure of a string. These fundamental PHP string functions let you determine the length of a string, search for the position of a substring, and extract portions of a string:


// Get string length
strlen("Hello World"); // 11

// Find position of first occurrence of substring
strpos("Hello World", "World"); // 6

// Find position of first occurrence of substring (case-insensitive)
stripos("Hello World", "world"); // 6

// Find position of last occurrence of substring
strrpos("Hello World World", "World"); // 12

// Return portion of string from start to specified length
substr("Hello World", 0, 5); // "Hello"

// Return portion of string from specified start position to end
substr("Hello World", 6); // "World"


These simple functions form the building blocks for most string operations. You‘ll find yourself reaching for them frequently to inspect user input, parse data formats, extract substrings, and beyond.

Modifying String Casing

Ensuring consistent casing is a common need, especially when dealing with user-entered content. PHP offers functions to convert between uppercase, lowercase, title case, and more:


// Uppercase first character
ucfirst("hello world"); // "Hello world"

// Uppercase first character of each word
ucwords("hello world"); // "Hello World"

// Uppercase all characters
strtoupper("Hello World"); // "HELLO WORLD"

// Lowercase first character
lcfirst("HELLO WORLD"); // "hELLO WORLD"

// Lowercase all characters
strtolower("Hello World"); // "hello world"


Standardizing casing helps create more normalized, consistent, and professional looking output. It‘s especially handy for things like article titles, user names, and product names.

Comparing Strings

Testing strings for equality is a fundamental operation. But there are many flavors of equality. Are two strings equal in a case-sensitive or case-insensitive way? In a binary or language-specific way? Should numbers embedded in the strings be compared numerically?

PHP provides an array of string comparison functions to handle common scenarios:


// Compare two strings (case-sensitive)
strcmp("hello", "Hello"); // 32

// Compare two strings (case-insensitive)
strcasecmp("hello", "Hello"); // 0

// Compare two strings using a "natural order" algorithm (case-sensitive)
strnatcmp("img1.png", "img12.png"); // <0

// Compare two strings using a "natural order" algorithm (case-insensitive)
strnatcasecmp("img1.png", "IMG12.PNG");// <0

// Compares two strings based on the current locale (case-sensitive)
strcoll("hello","hello"); // 0


The "natural order" comparison functions are especially handy for sorting strings in a human-friendly way, for example ordering "img2.png" before "img10.png".

Removing Whitespace

Trimming extraneous whitespace is another common need when accepting user input or parsing data. PHP makes it easy to trim whitespace from the start, end, or both sides of a string:


// Trim whitespace from start and end of string
trim(" Hello World "); // "Hello World"

// Trim whitespace from start of string
ltrim(" Hello World "); // "Hello World "

// Trim whitespace from end of string
rtrim(" Hello World "); // " Hello World"


These simple trimming functions help sanitize and normalize data. You‘ll often see them chained with other string functions when processing user input or importing messy data.

Replacing and Translating Characters

Efficiently replacing substrings or translating individual characters is the bread and butter of string manipulation. PHP offers a powerful suite of functions for finding and replacing:


// Replace all occurrences of a substring with a replacement
str_replace("World", "Universe", "Hello World"); // "Hello Universe"

// Replace all occurrences of a substring (case-insensitive)
str_ireplace("world", "Universe", "Hello World"); // "Hello Universe"

// Translate characters or substrings using a replacement table
$table = ["Hello" => "Hi", "world" => "earth"];
strtr("Hello world!", $table); // "Hi earth!"


The strtr function is especially powerful when you need to make multiple replacements in a single pass, for example when mapping HTML entities to their display characters.

Encoding and Escaping

The wild world of the web requires data to be encoded in a variety of ways for different purposes – URL encoding for GET parameters, HTML entity encoding for browser display, escapingcharacters for storing in a database, and so on.

PHP provides a solid set of functions for the most common encoding needs:


// URL encode a string
urlencode("Hello World!"); // "Hello%20World%21"

// URL decode a string
urldecode("Hello%20World%21"); // "Hello World!"

// HTML encode a string
htmlentities("5 < 7"); // "5 < 7"

// HTML decode a string
html_entity_decode("5 < 7"); // "5 < 7"

// Add backslashes before predefined characters
addslashes("It‘s Mario‘s \"Castle\""); // "It\‘s Mario\‘s \"Castle\""

// Strip backslashes added by addslashes()
stripslashes("It\‘s Mario\‘s \"Castle\""); // "It‘s Mario‘s "Castle""


These encoding and escaping functions are critical for handling untrusted input and ensuring your application is secure from injection attacks. They also help ensure data is transmitted and displayed correctly across different contexts.

Splitting and Joining Strings

Converting between strings and arrays is a key skill when dealing with structured string formats like CSV, query parameters, or file paths. PHP offers a variety of functions for splitting strings into arrays and joining arrays into strings:


// Split string by a delimiter into an array
explode(",", "apple,banana,pear"); // ["apple", "banana", "pear"]

// Join array elements into a string using a glue string
implode(", ", ["apple", "banana", "pear"]); // "apple, banana, pear"

// Split string into array of characters
str_split("Hello"); // ["H", "e", "l", "l", "o"]

// Parse a query string into variables
parse_str("name=John&age=30"); // $name = "John", $age = "30"

// Generate a query string from named values
http_build_query(["name" => "John", "age" => 30]); // "name=John&age=30"


Splitting and joining operations form the backbone of many data processing tasks. Whether parsing CSV files, building SQL statements, or constructing URLs, these functions will be your constant companions.

Hashing and Encrypting

Though not strictly part of the string function family, hashing and encryption functions often go hand-in-hand with string handling, especially when dealing with passwords or other sensitive data.

PHP provides a variety of hash functions for one-way mapping of strings to fixed-length digests:


// Calculate MD5 hash of string
md5("Hello World"); // "b10a8db164e0754105b7a99be72e3fe5"

// Calculate SHA1 hash of string
sha1("Hello World"); // "0a4d55a8d778e5022fab701977c5d840bbc486d0"

// Create a password hash using bcrypt
password_hash("mysecretpassword", PASSWORD_BCRYPT);
// "$2y$10$YxoiBQNhp1NeRPCP.KH1SenpqbL3rYfod9pKycBbtoFu9UM5zXdBu"


These functions are critical for secure handling of sensitive data. They ensure data like passwords are never stored in plaintext and help protect your application from rainbow table attacks.

Miscellaneous Functions

Beyond the core categories we‘ve covered, PHP includes a smorgasbord of other useful string functions for tasks like generating excerpts, converting between characters and ASCII codes, wordwrapping, and beyond. Here are a few greatest hits:


// Wrap string to specified line length
wordwrap("The quick brown fox jumps over the lazy dog.", 15, "
");
// "The quick brown
fox jumps over
the lazy dog."

// Reverses a string
strrev("Hello World!"); // "!dlroW olleH"

// Repeat a string a specified number of times
str_repeat("na ", 5) . "Batman!"; // "na na na na na Batman!"

// Get character for an ASCII value
chr(65); // "A"

// Get ASCII code for a character
ord("A"); // 65


These utility functions help provide the glue for many common string manipulations. Commit a few of them to memory and you‘ll quickly find opportunities to employ them.

Tips and Tricks

We‘ve toured an extensive collection of PHP string functions, but there are a few additional tips to keep in mind when working with strings in PHP:

• Many string functions accept and return byte positions rather than character positions. Be mindful of this distinction when working with multibyte character encodings.

• When doing repeated concatenation, it‘s often more efficient to build an array and implode it rather than using repeated concatenation operations.

• Some string functions like html_entity_decode are not safe to use on untrusted input as they can be leveraged for XSS attacks. Always sanitize user input before passing it to these functions.

• For more complex string parsing needs, consider using regular expressions with the PCRE functions rather than building long chains of string function calls.

Conclusion

We‘ve covered over 80 essential PHP string functions in this guide. While we can‘t possibly memorize them all, internalizing the key concepts will give you a strong foundation for efficient string handling.

Remember the core function groups – inspecting, modifying, comparing, splitting, joining, encoding, and hashing. Commit a few key functions from each group to memory, and you‘ll be well-equipped to tackle most common string manipulation tasks.

Most importantly, always be mindful of security when handling strings, especially with user-supplied input. Prefer escaping and encoding over string concatenation. Sanitize diligently, hash carefully, and you‘ll be well on your way to string mastery!