Section: POSIX Programmer's Manual (1P)
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.
--- topological sort
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
characters. Pairs of different items indicate ordering. Pairs of
identical items indicate presence, but not ordering.
The following operand shall be supported:
A pathname of a text file to order. If no
operand is given, the standard input shall be used.
The standard input shall be used if no
operand is specified, and shall be used if the
and the implementation treats the
as meaning standard input.
Otherwise, the standard input shall not be used.
See the INPUT FILES section.
The input file shall be a text file.
The following environment variables shall affect the execution of
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.)
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 and input files).
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
The standard output shall be a text file consisting of the order list
produced from the partially ordered input.
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.
variable need not affect the actions of
The output ordering is not lexicographic, but depends on the pairs of
items given as input.
a b c c d e
f g e f
produces the output:
The Base Definitions volume of POSIX.1-2008,
, Environment Variables
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
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