The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### 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 XBD 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
>   [XSI] 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

> XBD Environment Variables

#### CHANGE HISTORY

> First released in Issue 2.

#### Issue 6

> The normative text is reworded to avoid use of the term "must" for application requirements.

#### Issue 7

> Austin Group Interpretation 1003.1-2001 #092 is applied.

> The tsort utility is moved from the XSI option to the Base.

> POSIX.1-2008, Technical Corrigendum 1, XCU/TC1-2008/0146 [241] is applied.

End of informative text.

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