tsort - topological sort

The tsort utility writes to standard output a totally ordered list of items consistent with a partial ordering of items containing in the input.

The input consists of pairs of items (non-empty strings) separated by blanks. Pairs of different items indicate ordering. Pairs of identical items indicate presence, but not ordering.

The actions of tsort are not affected by the locale LC_COLLATE.

Syntax

tsort [file]

file

Name of the file to order.

file not specified:
The standard input is used. 

Error

Odd data:

There is an uneven number of fields in the input file.

Locale

The following environment variables affect the execution of tsort:

LANG

Provide a default value for the internationalization variables that are unset or null. If LANG is unset of null, the corresponding value from the implementation-specific default locale will be used. If any of the internationalization variables contains an invalid setting, the utility will behave as if none of the variables had been defined.

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- as opposed to multi-byte characters in arguments and input files), the classification of characters as upper- to lower-case, and the mapping of characters from one case to the other.

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.

Example

The command

$ tsort <<*EOF*
> a b c c d e
> g g
> f g e f
> g g
> h h
*EOF*

produces the output:

a
b
c
d
e
f
g
h