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tty - return user's terminal name
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 tty utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
While no input is read from standard input, standard input shall be examined to determine whether or not it is a terminal, and, if so, to determine the name of the terminal.
The following environment variables shall affect the execution of tty: LANG 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.) LC_ALL If set to a non-empty string value, override the values of all the other internationalization variables. LC_CTYPE 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). LC_MESSAGES 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. NLSPATH 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 the format: "not a tty\n"
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned: 0 Standard input is a terminal. 1 Standard input is not a terminal. >1 An error occurred.
CONSEQUENCES OF ERRORS
Default. The following sections are informative.
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).
The System Interfaces volume of IEEE Std 1003.1-2001, isatty(), ttyname()
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 .