with-input-from-string

(with-input-from-string (stream string) body...)

Binds stream to an input stream reading from string, evaluates the body forms, and returns the value of the last one. read-line consumes the string line by line and returns nil at the end; read parses one datum per line (like read on a file stream, it is line-oriented, so the rest of a line after the first datum is skipped). Works in all three backends.

Naming the bound variable *standard-input* redirects the whole stream-argument-less read family for the extent of the body -- including inside called functions -- because read-line, read-char, read and peek-char read the current (dynamically bound) value of *standard-input* at call time. A nil stream argument is the same designator, so a reader forwarding its own optional argument follows the redirect too; only t always names the process standard input.