This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
The logname utility shall write the user's login name to standard output. The login name shall be the string that would be returned by the getlogin() function defined in the System Interfaces volume of POSIX.1-2017. Under the conditions where the getlogin() function would fail, the logname utility shall write a diagnostic message to standard error and exit with a non-zero exit status.
The following environment variables shall affect the execution of logname:
Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2017, 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.
Determine the location of message catalogs for the processing of LC_MESSAGES.
The logname utility output shall be a single line consisting of the user's login name:
"%s\n", <login name>
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
An error occurred.
Consequences of Errors
The following sections are informative.
The logname utility explicitly ignores the LOGNAME environment variable because environment changes could produce erroneous results.
The passwd file is not listed as required because the implementation may have other means of mapping login names.
The Base Definitions volume of POSIX.1-2017, Chapter 8, Environment Variables
The System Interfaces volume of POSIX.1-2017, getlogin()
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
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