gvpr


SYNOPSIS
       gvpr  [-icnqV?]   [ -o outfile ] [ -a args ] [ 'prog' | -f progfile ] [
       files ]

DESCRIPTION
       gvpr (previously known as gpr) is a graph  stream  editor  inspired  by
       awk.  It copies input graphs to its output, possibly transforming their
       structure and attributes, creating new graphs,  or  printing  arbitrary
       information.   The  graph  model  is that provided by libcgraph(3).  In
       particular, gvpr reads and writes graphs using the dot language.

       Basically, gvpr traverses each input graph,  denoted  by  $G,  visiting
       each  node  and  edge, matching it with the predicate-action rules sup-
       plied in the input program.  The rules are  evaluated  in  order.   For
       each  predicate  evaluating  to  true, the corresponding action is per-
       formed.  During the traversal, the current node or edge  being  visited
       is denoted by $.

       For  each  input graph, there is a target subgraph, denoted by $T, ini-
       tially empty and used to accumulate  chosen  entities,  and  an  output
       graph,  $O,  used  for final processing and then written to output.  By
       default, the output graph is the target graph.  The output graph can be
       set in the program or, in a limited sense, on the command line.

OPTIONS
       The following options are supported:

       -a args
              The  string args is split into whitespace-separated tokens, with
              the individual tokens available as strings in the  gvpr  program
              as  ARGV[0],...,ARGV[ARGC-1].  Whitespace characters within sin-
              gle or double quoted substrings, or preceded by a backslash, are
              ignored  as separators.  In general, a backslash character turns
              off any special meaning of the following character.   Note  that
              the tokens derived from multiple -a flags are concatenated.

       -c     Use the source graph as the output graph.

       -i     Derive  the  node-induced subgraph extension of the output graph
              in the context of its root graph.

       -o outfile
              Causes the output stream to be written to the specified file; by
              default, output is written to stdout.

       -f progfile
              Use the contents of the specified file as the program to execute
              on the input. If progfile contains a slash character,  the  name
              is  taken  as the pathname of the file. Otherwise, gvpr will use
              the directories specified in the environment  variable  GVPRPATH
              to  look  for  the  file.  If -f is not given, gvpr will use the
              first non-option argument as the program.

OPERANDS
       The following operand is supported:

       files   Names of files containing 1 or more graphs in the dot language.
               If  no  -f  option is given, the first name is removed from the
               list and used as the input program. If the  list  of  files  is
               empty, stdin will be used.

PROGRAMS
       A  gvpr  program consists of a list of predicate-action clauses, having
       one of the forms:

              BEGIN { action }

              BEG_G { action }

              N [ predicate ] { action }

              E [ predicate ] { action }

              END_G { action }

              END { action }

       A program can contain at most one of each of the BEGIN, END_G  and  END
       clauses.   There  can  be  any number of BEG_G, N and E statements, the
       first applied to graphs, the second  to  nodes,  the  third  to  edges.
       These  are  separated  into  blocks,  a block consisting of an optional
       BEG_G statement and all N and E statements up to the next BEG_G  state-
       ment, if any.  The top-level semantics of a gvpr program are:

              Evaluate the BEGIN clause, if any.
              For each input graph G {
                  For each block {
                      Set G as the current graph and current object.
                      Evaluate the BEG_G clause, if any.
                      For each node and edge in G {
                          Set the node or edge as the current object.
                          Evaluate the N or E clauses, as appropriate.
                      }
                  }
                  Set G as the current object.
                  Evaluate the END_G clause, if any.
              }
              Evaluate the END clause, if any.

       The  actions  of  the BEGIN, BEG_G, END_G and END clauses are performed
       when the clauses are evaluated.  For N or E clauses, either the  predi-
       cate  or  action  may  be  omitted.   If  there is no predicate with an
       action, the action is performed on every node or edge, as  appropriate.
       If  there is no action and the predicate evaluates to true, the associ-
       ated node or edge is added to the target graph.

       The blocks are evaluated in the order in which they  occur.   Within  a
       In  addition  to  the usual C base types (void, int, char, float, long,
       unsigned and double), gvpr provides string as a synonym for char*,  and
       the  graph-based  types  node_t,  edge_t, graph_t and obj_t.  The obj_t
       type can be viewed as a supertype of the other 3  concrete  types;  the
       correct base type is maintained dynamically.  Besides these base types,
       the only other supported type expressions are (associative) arrays.

       Constants follow C syntax, but strings may be quoted with either  "..."
       or '...'.  gvpr accepts C++ comments as well as cpp-type comments.  For
       the latter, if a line begins with a '#' character, the rest of the line
       is ignored.

       A statement can be a declaration of a function, a variable or an array,
       or an executable statement. For declarations, there is a single  scope.
       Array declarations have the form:

               type array [ type0 ]

       where   type0   is optional. If it is supplied, the parser will enforce
       that all array subscripts have the specified type. If it  is  not  sup-
       plied,  objects of all types can be used as subscripts.  As in C, vari-
       ables and arrays must be declared. In particular, an  undeclared  vari-
       able will be interpreted as the name of an attribute of a node, edge or
       graph, depending on the context.

       Executable statements can be one of the following:

              { [ statement ... ] }
              expression                                              // commonly var = expression
              if( expression ) statement [ else statement ]
              for( expression ; expression ; expression ) statement
              for( array [ var ]) statement
              forr( array [ var ]) statement
              while( expression ) statement
              switch( expression ) case statements
              break [ expression ]
              continue [ expression ]
              return [ expression ]
       Items in brackets are optional.

       In the second form of the for statement and  the  forr  statement,  the
       variable  var  is  set  to each value used as an index in the specified
       array and then the associated statement is evaluated. For  numeric  and
       string  indices,  the  indices  are returned in increasing (decreasing)
       numeric or lexicographic order for for (forr, respectively).  This  can
       be used for sorting.

       Function definitions can only appear in the BEGIN clause.

       Expressions  include the usual C expressions.  String comparisons using
       == and != treat the right hand operand as a pattern for the purpose  of
       regular  expression  matching.   Patterns use ksh(1) file match pattern
       syntax.  (For simple string equality, use the strcmp function.

       As usual in the libcgraph(3) model, attributes are  string-valued.   In
       addition, gvpr supports certain pseudo-attributes of graph objects, not
       necessarily string-valued. These reflect intrinsic  properties  of  the
       graph objects and cannot be set by the user.

       head : node_t
              the head of an edge.

       tail : node_t
              the tail of an edge.

       name : string
              the  name of an edge, node or graph. The name of an edge has the
              form "<tail-name><edge-op><head-name>[<key>]",  where  <edge-op>
              is  "->"  or  "--" depending on whether the graph is directed or
              not. The bracket part [<key>] only appears if  the  edge  has  a
              non-trivial key.

       indegree : int
              the indegree of a node.

       outdegree : int
              the outdegree of a node.

       degree : int
              the degree of a node.

       root : graph_t
              the root graph of an object. The root of a root graph is itself.

       parent : graph_t
              the  parent  graph  of a subgraph. The parent of a root graph is
              NULL

       n_edges : int
              the number of edges in the graph

       n_nodes : int
              the number of nodes in the graph

       directed : int
              true (non-zero) if the graph is directed

       strict : int
              true (non-zero) if the graph is strict

BUILT-IN FUNCTIONS
       The following functions are built into gvpr. Those functions  returning
       references to graph objects return NULL in case of failure.

   Graphs and subgraph
       graph(s : string, t : string) : graph_t
              creates  a  graph whose name is s and whose type is specified by
              the string t. Ignoring case, the characters U, D, S, N have  the

       fstsubg(g : graph_t) : graph_t
              returns the first subgraph in graph g, or NULL if none exists.

       nxtsubg(sg : graph_t) : graph_t
              returns the next subgraph after sg, or NULL.

       isDirect(g : graph_t) : int
              returns true if and only if g is directed.

       isStrict(g : graph_t) : int
              returns true if and only if g is strict.

       nNodes(g : graph_t) : int
              returns the number of nodes in g.

       nEdges(g : graph_t) : int
              returns the number of edges in g.

   Nodes
       node(sg : graph_t, s : string) : node_t
              creates  a  node  in  graph  g of name s. If such a node already
              exists, it is returned.

       subnode(sg : graph_t, n : node_t) : node_t
              inserts the node n into the subgraph g. Returns the node.

       fstnode(g : graph_t) : node_t
              returns the first node in graph g, or NULL if none exists.

       nxtnode(n : node_t) : node_t
              returns the next node after n in the root graph, or NULL.

       nxtnode_sg(sg : graph_t, n : node_t) : node_t
              returns the next node after n in sg, or NULL.

       isNode(sg : graph_t, s : string) : node_t
              looks for a node in (sub)graph sg of name  s.  If  such  a  node
              exists, it is returned. Otherwise, NULL is returned.

       isSubnode(sg : graph_t, n : node_t) : int
              returns  non-zero  if node n is in (sub)graph sg, or zero other-
              wise.

       indegreeOf(sg : graph_t, n : node_t) : int
              returns the indegree of node n in (sub)graph sg.

       outdegreeOf(sg : graph_t, n : node_t) : int
              returns the outdegree of node n in (sub)graph sg.

       degreeOf(sg : graph_t, n : node_t) : int
              returns the degree of node n in (sub)graph sg.

   Edges
       edge(t : node_t, h : node_t, s : string) : edge_t
              inserts the edge e into the subgraph g. Returns the edge.

       isEdge(t : node_t, h : node_t, s : string) : edge_t
              looks for an edge with tail node t, head node h and name  s.  If
              the  graph  is undirected, the distinction between head and tail
              nodes is unimportant.  If such an edge exists, it  is  returned.
              Otherwise, NULL is returned.

       isEdge_sg(sg : graph_t, t : node_t, h : node_t, s : string) : edge_t
              looks  for  an  edge with tail node t, head node h and name s in
              (sub)graph sg. If  the  graph  is  undirected,  the  distinction
              between  head  and  tail  nodes is unimportant.  If such an edge
              exists, it is returned. Otherwise, NULL is returned.

       isSubedge(g : graph_t, e : edge_t) : int
              returns non-zero if edge e is in (sub)graph sg, or  zero  other-
              wise.

       fstout(n : node_t) : edge_t
              returns the first outedge of node n in the root graph.

       fstout_sg(sg : graph_t, n : node_t) : edge_t
              returns the first outedge of node n in (sub)graph sg.

       nxtout(e : edge_t) : edge_t
              returns the next outedge after e in the root graph.

       nxtout_sg(sg : graph_t, e : edge_t) : edge_t
              returns the next outedge after e in graph sg.

       fstin(n : node_t) : edge_t
              returns the first inedge of node n in the root graph.

       fstin_sg(sg : graph_t, n : node_t) : edge_t
              returns the first inedge of node n in graph sg.

       nxtin(e : edge_t) : edge_t
              returns the next inedge after e in the root graph.

       nxtin_sg(sg : graph_t, e : edge_t) : edge_t
              returns the next inedge after e in graph sg.

       fstedge(n : node_t) : edge_t
              returns the first edge of node n in the root graph.

       fstedge_sg(sg : graph_t, n : node_t) : edge_t
              returns the first edge of node n in graph sg.

       nxtedge(e : edge_t, node_t) : edge_t
              returns the next edge after e in the root graph.

       nxtedge_sg(sg : graph_t, e : edge_t, node_t) : edge_t
              returns the next edge after e in the graph sg.

       fwriteG(g : graph_t, fd : int) : void
              prints g in dot format onto the open stream denoted by the inte-
              ger fd.

       readG(fname : string) : graph_t
              returns a graph read from the file fname. The graph should be in
              dot format. If no graph can be read, NULL is returned.

       freadG(fd : int) : graph_t
              returns  the  next  graph read from the open stream fd.  Returns
              NULL at end of file.

   Graph miscellany
       delete(g : graph_t, x : obj_t) : void
              deletes object x from graph g.  If g is NULL, the function  uses
              the  root graph of x.  If x is a graph or subgraph, it is closed
              unless x is locked.

       isIn(g : graph_t, x : obj_t) : int
              returns true if x is in subgraph g.

       cloneG(g : graph_t, s : string) : graph_t
              creates a clone of graph g with name of s.  If s is "", the cre-
              ated graph has the same name as g.

       clone(g : graph_t, x : obj_t) : obj_t
              creates  a clone of object x in graph g.  In particular, the new
              object has the same name/value attributes and structure  as  the
              original  object.   If  an object with the same key as x already
              exists, its attributes are overlaid by those of x and the object
              is  returned.   If an edge is cloned, both endpoints are implic-
              itly cloned.  If a graph is cloned, all nodes,  edges  and  sub-
              graphs  are  implicitly cloned.  If x is a graph, g may be NULL,
              in which case the cloned object will be a  new  root  graph.  In
              this case, the call is equivalent to cloneG(x,"").

       copy(g : graph_t, x : obj_t) : obj_t
              creates  a copy of object x in graph g, where the new object has
              the same name/value attributes as the original  object.   If  an
              object with the same key as x already exists, its attributes are
              overlaid by those of x and the object is  returned.   Note  that
              this  is  a  shallow  copy.  If x is a graph, none of its nodes,
              edges or subgraphs are copied into the new graph.  If  x  is  an
              edge,  the  endpoints are created if necessary, but they are not
              cloned.  If x is a graph, g may  be  NULL,  in  which  case  the
              cloned object will be a new root graph.

       copyA(src : obj_t, tgt : obj_t) : int
              copies  the  attributes of object src to object tgt, overwriting
              any attribute values tgt may initially have.

       induce(g : graph_t) : void
              extends g to its node-induced subgraph  extension  in  its  root
              graph.
              returns  the value of attribute name in object src. This is use-
              ful for those cases when name conflicts with one of the keywords
              such  as  "head"  or  "root".   If  the  attribute  has not been
              declared in the graph, the function will initialize  it  with  a
              default  value  of "". To avoid this, one should use the hasAttr
              or isAttr function to check that the attribute exists.

       aset(src : obj_t, name : string, value : string) : int
              sets the value  of  attribute  name  in  object  src  to  value.
              Returns 0 on success, non-zero on failure. See aget above.

       getDflt(g : graph_t, kind : string, name : string) : string
              returns  the  default value of attribute name in objects in g of
              the given kind. For nodes, edges, and  graphs,  kind  should  be
              "N",  "E", and "G", respectively.  If the attribute has not been
              declared in the graph, the function will initialize  it  with  a
              default  value  of  "". To avoid this, one should use the isAttr
              function to check that the attribute exists.

       setDflt(g : graph_t, kind : string, name : string, value  :  string)  :
       int
              sets  the default value of attribute name to value in objects in
              g of the given kind. For nodes, edges, and graphs,  kind  should
              be  "N", "E", and "G", respectively.  Returns 0 on success, non-
              zero on failure. See getDflt above.

       fstAttr(g : graph_t, kind : string) : string
              returns the name of the first attribute of objects in g  of  the
              given  kind.  For  nodes, edges, and graphs, kind should be "N",
              "E", and "G", respectively.  If there  are  no  attributes,  the
              string "" is returned.

       nxtAttr(g : graph_t, kind : string, name : string) : string
              returns  the  name  of the next attribute of objects in g of the
              given kind after the attribute name.  The argument name must  be
              the  name  of  an  existing  attribute; it will typically be the
              return value of an previous call to  fstAttr  or  nxtAttr.   For
              nodes,  edges,  and  graphs,  kind  should be "N", "E", and "G",
              respectively.  If there are no attributes left, the string "" is
              returned.

       compOf(g : graph_t, n : node_t) : graph_t
              returns  the  connected component of the graph g containing node
              n, as a subgraph of g. The subgraph only contains the nodes. One
              can  use induce to add the edges. The function fails and returns
              NULL if n is not in g. Connectivity is based on  the  underlying
              undirected graph of g.

       kindOf(obj : obj_t) : string
              returns an indication of the type of obj.  For nodes, edges, and
              graphs, it returns "N", "E", and "G", respectively.

       lock(g : graph_t, v : int) : int
              implements graph locking on root graphs. If  the  integer  v  is

       gsub(str : string, pat : string) : string

       gsub(str : string, pat : string, repl : string) : string
              returns str with all substrings matching pat deleted or replaced
              by repl, respectively.

       sub(str : string, pat : string) : string

       sub(str : string, pat : string, repl : string) : string
              returns str with the leftmost substring matching pat deleted  or
              replaced  by  repl, respectively. The characters '^' and '$' may
              be used at the beginning and end, respectively, of pat to anchor
              the pattern to the beginning or end of str.

       substr(str : string, idx : int) : string

       substr(str : string, idx : int, len : int) : string
              returns the substring of str starting at position idx to the end
              of the string or of length len, respectively.   Indexing  starts
              at  0.  If  idx is negative or idx is greater than the length of
              str, a fatal error occurs. Similarly, in the second case, if len
              is  negative  or  idx + len is greater than the length of str, a
              fatal error occurs.

       strcmp(s1 : string, s2 : string) : int
              provides the standard C function strcmp(3).

       length(s : string) : int
              returns the length of string s.

       index(s : string, t : string) : int

       rindex(s : string, t : string) : int
              returns the index of the character in string s where  the  left-
              most  (rightmost)  copy  of string t can be found, or -1 if t is
              not a substring of s.

       match(s : string, p : string) : int
              returns the index of the character in string s where  the  left-
              most match of pattern p can be found, or -1 if no substring of s
              matches p.

       toupper(s : string) : string
              returns a version of s with the alphabetic characters  converted
              to upper-case.

       tolower(s : string) : string
              returns  a version of s with the alphabetic characters converted
              to lower-case.

       canon(s : string) : string
              returns a version of s appropriate to be used as  an  identifier
              in a dot file.

       xOf(s : string) : string
              returns the string "x" if s has the form "x,y", where both x and
              y are numeric.

       yOf(s : string) : string
              returns the string "y" if s has the form "x,y", where both x and
              y are numeric.

       llOf(s : string) : string
              returns    the    string   "llx,lly"   if   s   has   the   form
              "llx,lly,urx,ury", where all of  llx,  lly,  urx,  and  ury  are
              numeric.

       urOf(s)
              urOf(s  : string) : string returns the string "urx,ury" if s has
              the form "llx,lly,urx,ury", where all of llx, lly, urx, and  ury
              are numeric.

       sscanf(s : string, fmt : string, ...) : int
              scans the string s, extracting values according to the sscanf(3)
              format fmt.  The values are stored in  the  addresses  following
              fmt,  addresses  having  the  form  &v, where v is some declared
              variable of the correct type.  Returns the number of items  suc-
              cessfully scanned.

       split(s : string, arr : array, seps : string) : int

       split(s : string, arr : array) : int

       tokens(s : string, arr : array, seps : string) : int

       tokens(s : string, arr : array) : int
              The  split  function  breaks the string s into fields, while the
              tokens function breaks the string into tokens.  A field consists
              of all non-separator characters between two separator characters
              or the beginning or end of the string. Thus, a field may be  the
              empty string. A token is a maximal, non-empty substring not con-
              taining a separator character.   The  separator  characters  are
              those  given in the seps argument.  If seps is not provided, the
              default value is " \t\n".  The functions return  the  number  of
              fields or tokens.

              The  fields  and  tokens  are  stored in the argument array. The
              array must be string-valued and, if an index type is  specified,
              it must be int. The entries are indexed by consecutive integers,
              starting at 0. Any values already stored in the  array  will  be
              either  overwritten,  or  still  be  present  after the function
              returns.

   I/O
       print(...) : void
              print( expr, ... ) prints a string representation of each  argu-
              ment in turn onto stdout, followed by a newline.

              scans  in  values from an input stream according to the scanf(3)
              format fmt.  The values are stored in  the  addresses  following
              fmt,  addresses  having  the  form  &v, where v is some declared
              variable of the correct type.  By default, it reads from  stdin.
              If the optional integer fd is given, input is read from the open
              stream associated with fd.  Returns the number of items success-
              fully scanned.

       openF(s : string, t : string) : int
              opens  the file s as an I/O stream. The string argument t speci-
              fies how the file is opened. The arguments are the same  as  for
              the  C  function  fopen(3).   It returns an integer denoting the
              stream, or -1 on error.

              As usual, streams 0, 1 and 2 are already open as stdin,  stdout,
              and  stderr,  respectively. Since gvpr may use stdin to read the
              input graphs, the user should avoid using this stream.

       closeF(fd : int) : int
              closes the open stream denoted by the integer fd.  Streams  0, 1
              and 2 cannot be closed.  Returns 0 on success.

       readL(fd : int) : string
              returns  the next line read from the input stream fd. It returns
              the empty string "" on end of file. Note that the newline  char-
              acter is left in the returned string.

   Math
       exp(d : double) : double
              returns e to the dth power.

       log(d : double) : double
              returns the natural log of d.

       sqrt(d : double) : double
              returns the square root of the double d.

       pow(d : double, x : double) : double
              returns d raised to the xth power.

       cos(d : double) : double
              returns the cosine of d.

       sin(d : double) : double
              returns the sine of d.

       atan2(y : double, x : double) : double
              returns the arctangent of y/x in the range -pi to pi.

       MIN(y : double, x : double) : double
              returns the minimum of y and x.

       MAX(y : double, x : double) : double
              returns the maximum of y and x.

       unset(v : array) : void
              re-initializes the array.

   Miscellaneous
       exit(v : int) : void
              causes gvpr to exit with the exit code v.

       system(cmd : string) : int
              provides  the standard C function system(3).  It executes cmd in
              the user's shell environment, and returns the exit status of the
              shell.

       rand() : double
              returns a pseudo-random double between 0 and 1.

       srand() : int

       srand(v : int) : int
              sets  a seed for the random number generator. The optional argu-
              ment gives the seed; if it is omitted, the current time is used.
              The  previous  seed  value  is  returned. srand should be called
              before any calls to rand.

       colorx(color : string, fmt : string) : string
              translates a color from one format to another. The  color  argu-
              ment should be a color in one of the recognized string represen-
              tations. The fmt value should be one of "RGB", "RGBA", "HSV", or
              "HSVA".  An empty string is returned on error.

BUILT-IN VARIABLES
       gvpr provides certain special, built-in variables, whose values are set
       automatically by gvpr depending on the context. Except  as  noted,  the
       user cannot modify their values.

       $ : obj_t
              denotes  the current object (node, edge, graph) depending on the
              context.  It is not available in BEGIN or END clauses.

       $F : string
              is the name of the current input file.

       $G : graph_t
              denotes the current graph being processed. It is  not  available
              in BEGIN or END clauses.

       $NG : graph_t
              denotes the next graph to be processed. If $NG is NULL, the cur-
              rent graph $G is the last graph. Note that if  the  input  comes
              from  stdin, the last graph cannot be determined until the input
              pipe is closed.  It is not available in BEGIN or END clauses, or
              if the -n flag is used.

       $O : graph_t
              "gvpr_result".   If  used multiple times during the execution of
              gvpr, the name will be appended with an integer.  This  variable
              may be set by the user.

       $tvroot : node_t
              indicates  the  starting  node  for  a  (directed or undirected)
              depth-first or breadth-first traversal of the graph (cf. $tvtype
              below).   The default value is NULL for each input graph.  After
              the traversal at the given root, if the  value  of  $tvroot  has
              changed,  a  new  traversal  will  begin  with  the new value of
              $tvroot. Also, set $tvnext below.

       $tvnext : node_t
              indicates the next starting node for a (directed or  undirected)
              depth-first or breadth-first traversal of the graph (cf. $tvtype
              below).  If a traversal finishes and the $tvroot  has  not  been
              reset  but the $tvnext has been set but not used, this node will
              be used as the next choice for $tvroot.  The  default  value  is
              NULL for each input graph.

       $tvedge : edge_t
              For  BFS  and  DFS  traversals,  this is set to the edge used to
              arrive at the current node or edge. At the beginning of  a  tra-
              versal, or for other traversal types, the value is NULL.

       $tvtype : tvtype_t
              indicates  how  gvpr  traverses a graph. It can only take one of
              the constant values  with  the  previx  "TV_"  described  below.
              TV_flat is the default.

              In  the  underlying graph library cgraph(3), edges in undirected
              graphs are given an arbitrary direction. This is used  for  tra-
              versals, such as TV_fwd, requiring directed edges.

       ARGC : int
              denotes  the  number  of arguments specified by the -a args com-
              mand-line argument.

       ARGV : string array
              denotes the array of arguments specified by the -a args command-
              line argument. The ith argument is given by ARGV[i].

BUILT-IN CONSTANTS
       There are several symbolic constants defined by gvpr.

       NULL : obj_t
              a null object reference, equivalent to 0.

       TV_flat : tvtype_t
              a  simple,  flat  traversal, with graph objects visited in seem-
              ingly arbitrary order.

       TV_ne : tvtype_t
              a traversal which first visits all of the nodes, then all of the
              had  previously (at the start, the previous value is initialized
              to NULL.), gvpr will simply look for  some  unvisited  node  and
              traverse  its connected component. On the other hand, if $tvroot
              has changed, its connected component will be toured, assuming it
              has not been previously visited or, if $tvroot is NULL, the tra-
              versal will stop. Note that using TV_dfs and $tvroot, it is pos-
              sible to create an infinite loop.

              By  default, the traversal is done in pre-order. That is, a node
              is visited before all of its unvisited  edges.  For  TV_postdfs,
              all of a node's unvisited edges are visited before the node. For
              TV_prepostdfs, a node is visited twice, before and after all  of
              its unvisited edges.

       TV_fwd : tvtype_t
       TV_postfwd : tvtype_t
       TV_prepostfwd : tvtype_t
              A traversal of the graph using a depth-first search on the graph
              following only forward arcs.  The choice of roots for  the  tra-
              versal is the same as described for TV_dfs above.  The different
              order of visitation specified by TV_fwd, TV_postfwd and  TV_pre-
              postfwd are the same as those specified by the analogous traver-
              sals TV_dfs, TV_postdfs and TV_prepostdfs.

       TV_rev : tvtype_t
       TV_postrev : tvtype_t
       TV_prepostrev : tvtype_t
              A traversal of the graph using a depth-first search on the graph
              following  only  reverse arcs.  The choice of roots for the tra-
              versal is the same as described for TV_dfs above.  The different
              order  of visitation specified by TV_rev, TV_postrev and TV_pre-
              postrev are the same as those specified by the analogous traver-
              sals TV_dfs, TV_postdfs and TV_prepostdfs.

       TV_bfs : tvtype_t
              A  traversal  of  the  graph using a breadth-first search on the
              graph ignoring edge directions. See the item on TV_dfs above for
              the role of $tvroot.

EXAMPLES
              gvpr -i 'N[color=="blue"]' file.gv

       Generate the node-induced subgraph of all nodes with color blue.

              gvpr -c 'N[color=="blue"]{color = "red"}' file.gv

       Make all blue nodes red.

              BEGIN { int n, e; int tot_n = 0; int tot_e = 0; }
              BEG_G {
                n = nNodes($G);
                e = nEdges($G);
                printf ("%d nodes %d edges %s\n", n, e, $G.name);
                tot_n += n;
                node_t h = clone(g,$.head);
                node_t t = clone(g,$.tail);
                edge_t e = edge(t,h,"");
                e.weight = e.weight + 1;
              }
              END_G { $O = g; }

       Produces  a  strict  version  of  the  input  graph,  where  the weight
       attribute of an edge indicates how many edges from the input graph  the
       edge represents.

              BEGIN {node_t n; int deg[]}
              E{deg[head]++; deg[tail]++; }
              END_G {
                for (deg[n]) {
                  printf ("deg[%s] = %d\n", n.name, deg[n]);
                }
              }

       Computes the degrees of nodes with edges.

              BEGIN {
                int i, indent;
                int seen[string];
                void prInd (int cnt) {
                  for (i = 0; i < cnt; i++) printf ("  ");
                }
              }
              BEG_G {

                 $tvtype = TV_prepostfwd;
                 $tvroot = node($,ARGV[0]);
              }
              N {
                if (seen[$.name]) indent--;
                else {
                  prInd(indent);
                    print ($.name);
                  seen[$.name] = 1;
                  indent++;
                }
              }

       Prints  the  depth-first traversal of the graph, starting with the node
       whose name is ARGV[0], as an indented list.

ENVIRONMENT
       GVPRPATH
              Colon-separated list of directories to be searched to  find  the
              file  specified  by the -f option. gvpr has a default list built
              in. If GVPRPATH is not defined, the default  list  is  used.  If
              GVPRPATH  starts  with  colon,  the  list is formed by appending
              GVPRPATH to the default list. If GVPRPATH ends with  colon,  the
              list is formed by appending the default list to GVPRPATH. Other-

       in  gvpr.  To  avoid  this,  it  is  best to wrap the program in single
       quotes.

       If string constants contain pattern metacharacters  that  you  want  to
       escape to avoid pattern matching, two backslashes will probably be nec-
       essary, as a single backslash will be lost when the  string  is  origi-
       nally  scanned.  Usually,  it is simpler to use strcmp to avoid pattern
       matching.

       As of 24 April 2008, gvpr switched to using  a  new,  underlying  graph
       library,  which uses the simpler model that there is only one copy of a
       node, not one copy for each  subgraph  logically  containing  it.  This
       means  that  iterators such as nxtnode cannot traverse a subgraph using
       just a node argument. For this reason, subgraph traversal requires  new
       functions  ending  in  "_sg",  which also take a subgraph argument. The
       versions without that suffix will always traverse the root graph.

       There is a single global scope, except for formal function  parameters,
       and  even these can interfere with the type system. Also, the extent of
       all variables is the entire life of the program.  It might  be  prefer-
       able  for  scope  to reflect the natural nesting of the clauses, or for
       the program to at least reset locally declared variables.  For now,  it
       is advisable to use distinct names for all variables.

       If  a  function ends with a complex statement, such as an IF statement,
       with each branch doing a return, type  checking  may  fail.   Functions
       should use a return at the end.

       The  expr  library  does  not  support string values of (char*)0.  This
       means we can't distinguish between "" and (char*)0 edge keys.  For  the
       purposes  of  looking  up  and  creating  edges,  we translate "" to be
       (char*)0, since this latter value is necessary in order to look up  any
       edge with a matching head and tail.

       Related  to this, strings converted to integers act like char pointers,
       getting the value 0 or 1  depending  on  whether  the  string  consists
       solely of zeroes or not. Thus, the ((int)"2") evaluates to 1.

       The  language inherits the usual C problems such as dangling references
       and the confusion between '=' and '=='.

AUTHOR
       Emden R. Gansner <erg@research.att.com>

SEE ALSO
       awk(1), gc(1), dot(1), nop(1), expr(3), cgraph(3)



                                29 August 2013                         GVPR(1)
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