rtrim

rtrim is a string processing function used to remove characters from the end of a string. In PHP, rtrim removes any trailing characters that appear in a specified character mask. If no mask is provided, it defaults to removing whitespace characters from the end of the string.

Syntax and parameters: rtrim(string, charlist). The first argument is the input string. The optional second argument, charlist, contains characters to be stripped from the end. If charlist is omitted, the function trims whitespace, including space, tab, newline, carriage return, NUL, and vertical tab, from the right end of the string. The operation is performed on a byte level and is not inherently Unicode-aware.

Behavior and considerations: rtrim only affects trailing characters, not those in the middle or at the start of the string. Because it uses a character mask rather than a pattern, the exact characters removed depend on what appears in the mask. For Unicode strings, rtrim may not handle multibyte whitespace correctly; consider using multibyte string functions or regular expressions for Unicode-safe trimming.

Examples: rtrim("Hello world ") returns "Hello world". rtrim("foo123", "123") returns "foo".

Related functions: rtrim is the right-side counterpart to ltrim (which trims characters from the left) and trim (which trims from both ends). In SQL, a similar operation is performed by RTRIM, which typically removes trailing spaces from strings, though behavior can vary by database.