All these functions are used to manipulate strings. They are part of the PHP core, so you don't have to install anything to use these functions.

addcslashes

This function is used to quote a given string with slashes in a C style format.

addslashes

This function is used to quote string with slashes.

bin2hex

This function is used to convert binary data into hexadecimal representation.

chop

This function is an alias of rtrim.

chr

This function is used to return a specific character.

chunk_split

This function is used to split a string into smaller chunks.

convert_cyr_string 

This function is used to convert from one Cyrillic character set to another.

convert_uudecode 

This function is used to decode a uuencoded string.

convert_uuencode

This function is used to uuencode a string.

count_chars 

This function is used to return information about characters used in a string.

crc32

This function is used to calculates the crc32 polynomial of a string.

crypt 

This function is used to one-way string hashing.

echo 

This function is used to output one or more strings.

explode

This function is used to split a string by string.

fprintf

This function is used to write a formatted string to a stream.

get_html_translation_table

This function is used to returns the translation table used by htmlspecialchars and htmlentities.

hebrev 

This function is used to convert logical Hebrew text to visual text.

hebrevc

This function is used to convert logical Hebrew text to visual text with newline conversion.

hex2bin

This function is used to decodes a hexadecimally encoded binary string.

html_entity_decode 

This function is used to convert all HTML entities to their applicable characters.

htmlentities

This function is used to convert all applicable characters to HTML entities.

htmlspecialchars_decode

This function is used to convert special HTML entities back to characters.

htmlspecialchars

This function is used to convert special characters to HTML entities.

implode

This function is used to join array elements with a string.

join

This function is an alias of implode.

lcfirst 

This function is used to make a string's first character lowercase.

levenshtein 

This function is used to calculate Levenshtein distance between two strings.

localeconv

This function is used to get numeric formatting information.

ltrim

This function is used to strip whitespace (or other characters) from the beginning of a string.

md5_file

This function is used to calculates the md5 hash of a given file.

md5

This function is used to calculate the md5 hash of a string.

metaphone

This function is used to calculate the metaphone key of a string.

money_format

This function is used to formats a number as a currency string.

nl_langinfo

This function is used to query language and locale information.

nl2br

This function is used to inserts HTML line breaks before all newlines in a string.

number_format

This function is used to format a number with grouped thousands.

ord

This function is used to return ASCII value of character.

parse_str

This function is used to parses the string into variables.

print

This function is used to output a string.

printf

This function is used to output a formatted string.

quoted_printable_decode

This function is used to convert a quoted-printable string to an 8 bit string.

quoted_printable_encode

This function is used to convert a 8 bit string to a quoted-printable string.\

quotemeta

This function is used to quote meta characters.

rtrim

This function is used to strip whitespace (or other characters) from the end of a string.

setlocale

This function is used to set locale information.

sha1_file 

This function is used to calculate the sha1 hash of a file.

sha1

This function is used to calculate the sha1 hash of a string.

similar_text

This function is used to calculate the similarity between two strings.

soundex

This function is used to calculate the soundex key of a string.

sprintf

This function is used to return a formatted string.

sscanf

This function is used to parses input from a string according to a format.

str_getcsv

This function is used to parse a CSV string into an array.

str_ireplace

This function is used to case-insensitive version of str_replace.

str_pad

This function is used to pad a string to a certain length with another string.

str_repeat

This function is used to repeat a string.

str_replace

This function is used to replace all occurrences of the search string with the replacement string.

str_rot13

This function is used to perform the rot13 transform on a string.

str_shuffle

This function is used to randomly shuffles a string.

str_split

This function is used to convert a string to an array.

str_word_count

This function is used to return information about words used in a string.

strcasecmp

This function is used to binary safe case-insensitive string comparison.

strchr

This function is an alias of strstr.

strcmp

This function is used to binary safe string comparison.

strcoll

This function is used to locale based string comparison.

strcspn

This function is used to find length of initial segment not matching mask.

strip_tags

This function is used to strip HTML and PHP tags from a string.

stripcslashes

This function is used to un-quote string quoted with addcslashes.

stripos

This function is used to find the position of the first occurrence of a case-insensitive substring in a string.

stripslashes

This function is used to un-quotes a quoted string.

stristr

This function is used to case-insensitive strstr.

strlen

This function is used to get string length.

strnatcasecmp

This function is used to case insensitive string comparisons using a "natural order" algorithm.

strnatcmp

This function is used to string comparisons using a "natural order" algorithm.

strncasecmp

This function is used to binary safe case-insensitive string comparison of the first n characters.

strncmp

This function is used to binary safe string comparison of the first n characters.

strpbrk

This function is used to search a string for any of a set of characters.

strpos

This function is used to find the position of the first occurrence of a substring in a string.

strrchr

This function is used to find the last occurrence of a character in a string.

strrev

This function is used to reverse a string.

strripos

This function is used to find the position of the last occurrence of a case-insensitive substring in a string.

strrpos

This function is used to find the position of the last occurrence of a substring in a string.

strspn

This function is used to finds the length of the initial segment of a string consisting entirely of characters contained within a given mask.

strstr

This function is used to find the first occurrence of a string.

strtok

This function is used to tokenize string.

strtolower

This function is used to make a string lowercase.

strtoupper

This function is used to make a string uppercase.

strtr

This function is used to translate characters or replace substrings.

substr_compare

This function is used to binary safe comparison of two strings from an offset, up to length characters.

substr_count

This function is used to count the number of substring occurrences.

substr_replace

This function is used to replace text within a portion of a string.

substr

This function is used to return part of a string.

trim

This function is used to strip whitespace (or other characters) from the beginning and end of a string.

ucfirst

This function is used to make a string's first character uppercase.

ucwords

This function is used to uppercase the first character of each word in a string.

vfprintf

This function is used to write a formatted string to a stream.

vprintf

This function is used to output a formatted string.

vsprintf

This function is used to return a formatted string.

wordwrap

This function is used to wraps a string to a given number of characters.