# tsort

## 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.1‐2017, _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.
    


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