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PROLOG
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.
NAME
tsort — topological sort
SYNOPSIS
tsort [file]
DESCRIPTION
The tsort utility shall write to standard output a totally ordered list of items consistent with a
partial ordering of items contained in the input.
The application shall ensure that the input consists of pairs of items (non-empty strings) separated by
<blank> characters. Pairs of different items indicate ordering. Pairs of identical items indicate
presence, but not ordering.
OPTIONS
None.
OPERANDS
The following operand shall be supported:
file A pathname of a text file to order. If no file operand is given, the standard input shall be
used.
STDIN
The standard input shall be used if no file operand is specified, and shall be used if the file operand
is '−' and the implementation treats the '−' as meaning standard input. Otherwise, the standard input
shall not be used. See the INPUT FILES section.
INPUT FILES
The input file shall be a text file.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of tsort:
LANG Provide a default value for the internationalization variables that are unset or null. (See the
Base Definitions volume of POSIX.1‐2008, 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 and input files).
LC_MESSAGES
Determine the locale that should be used to affect the format and contents of diagnostic
messages written to standard error.
NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES.
ASYNCHRONOUS EVENTS
Default.
STDOUT
The standard output shall be a text file consisting of the order list produced from the partially ordered
input.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The LC_COLLATE variable need not affect the actions of tsort. The output ordering is not lexicographic,
but depends on the pairs of items given as input.
EXAMPLES
The command:
tsort <<EOF
a b c c d e
g g
f g e f
h h
EOF
produces the output:
a
b
c
d
e
f
g
h
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .