A string is series of characters, where a character is the same as a byte.

A string literal can be specified in four different ways:

•     single quoted
•     double quoted
•     heredoc syntax
•     nowdoc syntax (since PHP 5.3.0)

PHP String Functions

• addcslashes — Quote string with slashes in a C style
• addslashes — Quote string with slashes
• bin2hex — Convert binary data into hexadecimal representation
• chop — Alias of rtrim
• chr — Return a specific character
• chunk_split — Split a string into smaller chunks
• convert_cyr_string — Convert from one Cyrillic character set to another
• convert_uudecode — Decode a uuencoded string
• convert_uuencode — Uuencode a string
• count_chars — Return information about characters used in a string
• crc32 — Calculates the crc32 polynomial of a string
• crypt — One-way string hashing
• echo — Output one or more strings
• explode — Split a string by string
• fprintf — Write a formatted string to a stream
• get_html_translation_table — Returns the translation table used by htmlspecialchars and htmlentities
• hebrev — Convert logical Hebrew text to visual text
• hebrevc — Convert logical Hebrew text to visual text with newline conversion
• hex2bin — Decodes a hexadecimally encoded binary string
• html_entity_decode — Convert all HTML entities to their applicable characters
• htmlentities — Convert all applicable characters to HTML entities
• htmlspecialchars_decode — Convert special HTML entities back to characters
• htmlspecialchars — Convert special characters to HTML entities
• implode — Join array elements with a string
• join — Alias of implode
• lcfirst — Make a string's first character lowercase
• levenshtein — Calculate Levenshtein distance between two strings
• localeconv — Get numeric formatting information
• ltrim — Strip whitespace (or other characters) from the beginning of a string
• md5_file — Calculates the md5 hash of a given file
• md5 — Calculate the md5 hash of a string
• metaphone — Calculate the metaphone key of a string
• money_format — Formats a number as a currency string
• nl_langinfo — Query language and locale information
• nl2br — Inserts HTML line breaks before all newlines in a string
• number_format — Format a number with grouped thousands
• ord — Return ASCII value of character
• parse_str — Parses the string into variables
• print — Output a string
• printf — Output a formatted string
• quoted_printable_decode — Convert a quoted-printable string to an 8 bit string
• quoted_printable_encode — Convert a 8 bit string to a quoted-printable string
• quotemeta — Quote meta characters
• rtrim — Strip whitespace (or other characters) from the end of a string
• setlocale — Set locale information
• sha1_file — Calculate the sha1 hash of a file
• sha1 — Calculate the sha1 hash of a string
• similar_text — Calculate the similarity between two strings
• soundex — Calculate the soundex key of a string
• sprintf — Return a formatted string
• sscanf — Parses input from a string according to a format
• str_getcsv — Parse a CSV string into an array
• str_ireplace — Case-insensitive version of str_replace.
• str_pad — Pad a string to a certain length with another string
• str_repeat — Repeat a string
• str_replace — Replace all occurrences of the search string with the replacement string
• str_rot13 — Perform the rot13 transform on a string
• str_shuffle — Randomly shuffles a string
• str_split — Convert a string to an array
• str_word_count — Return information about words used in a string
• strcasecmp — Binary safe case-insensitive string comparison
• strchr — Alias of strstr
• strcmp — Binary safe string comparison
• strcoll — Locale based string comparison
• strcspn — Find length of initial segment not matching mask
• strip_tags — Strip HTML and PHP tags from a string
• stripcslashes — Un-quote string quoted with addcslashes
• stripos — Find the position of the first occurrence of a case-insensitive substring in a string
• stripslashes — Un-quotes a quoted string
• stristr — Case-insensitive strstr
• strlen — Get string length
• strnatcasecmp — Case insensitive string comparisons using a "natural order" algorithm
• strnatcmp — String comparisons using a "natural order" algorithm
• strncasecmp — Binary safe case-insensitive string comparison of the first n characters
• strncmp — Binary safe string comparison of the first n characters
• strpbrk — Search a string for any of a set of characters
• strpos — Find the position of the first occurrence of a substring in a string
• strrchr — Find the last occurrence of a character in a string
• strrev — Reverse a string
• strripos — Find the position of the last occurrence of a case-insensitive substring in a string
• strrpos — Find the position of the last occurrence of a substring in a string
• strspn — Finds the length of the initial segment of a string consisting entirely of characters contained within a given mask.
• strstr — Find the first occurrence of a string
• strtok — Tokenize string
• strtolower — Make a string lowercase
• strtoupper — Make a string uppercase
• strtr — Translate characters or replace substrings
• substr_compare — Binary safe comparison of two strings from an offset, up to length characters
• substr_count — Count the number of substring occurrences
• substr_replace — Replace text within a portion of a string
• substr — Return part of a string
• trim — Strip whitespace (or other characters) from the beginning and end of a string
• ucfirst — Make a string's first character uppercase
• ucwords — Uppercase the first character of each word in a string
• vfprintf — Write a formatted string to a stream
• vprintf — Output a formatted string
• vsprintf — Return a formatted string
• wordwrap — Wraps a string to a given number of characters