tsort

PURPOSE

     Sorts an  unordered list of ordered  pairs (a topological
     sort).

SYNOPSIS
     tsort [ file ]


DESCRIPTION

     The tsort  command reads from  file or standard  input an
     unordered list  of ordered pairs, it  builds a completely
     ordered list, and writes it to standard output.

     The input  file should contain pairs  of nonempty strings
     separated by blanks.  Pairs of different items indicate a
     relative order.  Pairs of  identical items indicate pres-
     ence, but no  relative order.  You can use  tsort to sort
     the output of the lorder command.

     If file  contains an odd  number of fields,  tsort writes
     the error message "Odd data".

EXAMPLE

     To create a subroutine library:

       lorder  charin.o  scanfld.o  scan.o  scanln.o  \
       |  tsort  |  xargs  ar  qv  libsubs.a

     This creates a subroutine  library named "libsubs.a" that
     contains    "charin.o",   "scanfld.o",    "scan.o",   and
     "scanln.o".  The  ordering of  the object modules  in the
     library  is  important.   The ld  command  requires  each
     module to precede all the  other modules that it calls or
     references.  The  lorder and tsort commands  together add
     the subroutines to the library in the proper order.

     Suppose that  "scan.o" calls "scanfld.o"  and "scanln.o".
     "scanfld.o"  also calls  "charin.o".   First, the  lorder
     command creates a list of  pairs that shows these depend-
     encies:

       charin.o charin.o
       scanfld.o scanfld.o
       scan.o scan.o
       scanln.o scanln.o
       scanfld.o charin.o
       scanln.o charin.o
       scan.o scanfld.o

     Next, the "|" (vertical bar) sends this list to the tsort
     command, which converts it into the ordering we need:

       scan.o
       scanfld.o
       scanln.o
       charin.o

     Note  that  each module  precedes  the  module it  calls.
     "charin.o", which does not call another module, is last.

     The second "|" then sends  this list to xargs, which con-
     structs and runs the following ar command:

       ar qv libsubs.a scan.o scanfld.o scanln.o charin.o

     This ar command creates the properly ordered library.

RELATED INFORMATION

     The following commands:  "ar," "lorder," and  "xargs."