PHP’s filter functions can be used for validation or sanitizing. These filters are used for sanitizing. This means it will alter the data if needed to meet the requirements as defined by the filter used.

ID	Flags
FILTER_SANITIZE_EMAIL
FILTER_SANITIZE_ENCODED	FILTER_FLAG_STRIP_LOW, FILTER_FLAG_STRIP_HIGH, FILTER_FLAG_ENCODE_LOW, FILTER_FLAG_ENCODE_HIGH
FILTER_SANITIZE_MAGIC_QUOTES
FILTER_SANITIZE_NUMBER_FLOAT	FILTER_FLAG_ALLOW_FRACTION, FILTER_FLAG_ALLOW_THOUSAND, FILTER_FLAG_ALLOW_SCIENTIFIC
FILTER_SANITIZE_NUMBER_INT
FILTER_SANITIZE_SPECIAL_CHARS	FILTER_FLAG_STRIP_LOW, FILTER_FLAG_STRIP_HIGH, FILTER_FLAG_ENCODE_HIGH
FILTER_SANITIZE_STRING (or FILTER_SANITIZE_STRIPPED)	FILTER_FLAG_NO_ENCODE_QUOTES, FILTER_FLAG_STRIP_LOW, FILTER_FLAG_STRIP_HIGH, FILTER_FLAG_ENCODE_LOW, FILTER_FLAG_ENCODE_HIGH, FILTER_FLAG_ENCODE_AMP
FILTER_SANITIZE_URL
FILTER_UNSAFE_RAW	FILTER_FLAG_STRIP_LOW, FILTER_FLAG_STRIP_HIGH, FILTER_FLAG_ENCODE_LOW, FILTER_FLAG_ENCODE_HIGH, FILTER_FLAG_ENCODE_AMP

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FILTER_SANITIZE_EMAIL: Remove all characters except letters, digits and !#$%&’*+-/=?^_`{|}~@.[]

FILTER_SANITIZE_ENCODED: URL-encode string, optionally strip or encode special characters

FILTER_SANITIZE_MAGIC_QUOTES: Apply addslashes()

FILTER_SANITIZE_NUMBER_FLOAT: Remove all characters except digits, +- and optionally .,eE

FILTER_SANITIZE_NUMBER_INT: Remove all characters except digits, plus and minus sign

FILTER_SANITIZE_SPECIAL_CHARS: HTML-escape ‘”<>& and characters with ASCII value less than 32, optionally strip or encode other special characters

FILTER_SANITIZE_STRING: Strip tags, optionally strip or encode special characters

FILTER_SANITIZE_URL: Remove all characters except letters, digits and $-_.+!*’(),{}|\\^~[]`<>#%”;/?:@&=

FILTER_UNSAFE_RAW: Do nothing, optionally strip or encode special characters