The tty utility shall write to the standard output the name of the
terminal that is open as standard input. The name that is used shall be
equivalent to the string that would be returned by the ttyname()
function defined in the System Interfaces volume of
IEEE Std 1003.1-2001.
The following environment variables shall affect the execution of tty:
Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to standard error and
informative messages written to standard output.
Determine the location of message catalogs for the
processing of LC_MESSAGES.
If standard input is a terminal device, a pathname of the terminal as specified
by the ttyname() function defined in the System Interfaces volume of
IEEE Std 1003.1-2001 shall be written in the following format:
"%s\n", <terminal name>
Otherwise, a message shall be written indicating that standard input is not
connected to a terminal. In the POSIX locale, the tty utility shall use
This utility checks the status of the file open as standard input against that
of an implementation-defined set of files. It is possible that no match can be
found, or that the match found need not be the same file as that which was
opened for standard input (although they are the same device).
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html