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*terminal-io*

∗terminal-io∗ Variable

Value Type:

a bidirectional stream.

Initial Value:

implementation-dependent, but it must be an open stream that is not a generalized synonym stream to an I/O customization variables but that might be a generalized synonym stream to the value of some I/O customization variable.

Description:

The value of *terminal-io*, called terminal I/O, is ordinarily a bidirectional stream that connects to the user’s console. Typically, writing to this stream would cause the output to appear on a display screen, for example, and reading from the stream would accept input from a keyboard. It is intended that standard input functions such as read and read-char, when used with this stream, cause echoing of the input into the output side of the stream. The means by which this is accomplished are implementation-dependent.

The effect of changing the value of *terminal-io*, either by binding or assignment, is implementation-defined.

Examples:

(progn (prin1 ’foo) (prin1 ’bar \*terminal-io\*)) 

▷ FOOBAR 
→ BAR 
(with-output-to-string (\*standard-output\*) 
  (prin1 ’foo) 
  (prin1 ’bar \*terminal-io\*)) 
▷ BAR 
→ "FOO"

See Also:

*debug-io*, *error-output*, *query-io*, *standard-input*, *standard-output*, *trace-output* stream-error Condition Type

Class Precedence List:

stream-error, error, serious-condition, condition, t

Description:

The type stream-error consists of error conditions that are related to receiving input from or sending output to a stream. The “offending stream” is initialized by the :stream initialization argument to make-condition, and is accessed by the function stream-error-stream.

See Also:

stream-error-stream

Expanded Reference: *terminal-io*​

Overview​

*terminal-io* is a special variable whose value is a bidirectional stream connected to the user's console. Output to this stream typically appears on the display, and input is accepted from the keyboard.

It Is a Stream​

(streamp *terminal-io*)
=> T

It Is Bidirectional​

(list (input-stream-p *terminal-io*)
      (output-stream-p *terminal-io*))
=> (NIL T)

Direct Output Bypasses Redirection​

Even when *standard-output* is redirected, writing directly to *terminal-io* still goes to the terminal.

(with-output-to-string (*standard-output*)
  (prin1 'foo)                     ; goes to the string
  (prin1 'bar *terminal-io*))     ; goes to the terminal
; "bar" is printed to the terminal
=> "FOO"

Relationship to Standard I/O Variables​

The standard I/O customization variables (*standard-input*, *standard-output*, etc.) are often initially synonym streams to *terminal-io*. Rebinding those variables redirects I/O, while *terminal-io* remains connected to the console.