Manual: gvpr
GVPR(1) General Commands Manual GVPR(1)
NAME
gvpr - graph pattern scanning and processing language
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, posā
sibly 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 prediā
cateāaction rules supplied in the input program. The rules are evaluated in order. For each predicate evaluating to
true, the corresponding action is performed. 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, initially empty and used to accumulate chosen entiā
ties, 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 whitespaceāseparated tokens, with the individual tokens available as strings in
the gvpr program as ARGV[0],...,ARGV[ARGC-1]. Whitespace characters within single or double quoted subā
strings, 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 conā
catenated.
-c Use the source graph as the output graph.
-i Derive the nodeāinduced 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 nonāopā
tion argument as the program.
-q Turns off warning messages.
-n Turns off graph read-ahead. By default, the variable $NG is set to the next graph to be processed. This reā
quires a read of the next graph before processing the current graph, which may block if the next graph is only
generated in response to some action pertaining to the processing of the current graph.
-v Enable verbose messages.
-V Causes the program to print version information and exit.
-? Causes the program to print usage information and exit.
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 predicateāaction 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 statement,
if any. The topālevel 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 predicate or action may be omitted. If there is no predicate with an action, the action is perā
formed on every node or edge, as appropriate. If there is no action and the predicate evaluates to true, the associā
ated node or edge is added to the target graph.
The blocks are evaluated in the order in which they occur. Within a block, the N clauses (E clauses, respectively)
are evaluated in the order in which they occur. Note, though, that within a block, N or E clauses may be interlaced,
depending on the traversal order.
Predicates and actions are sequences of statements in the C dialect supported by the expr(3) library. The only difā
ference between predicates and actions is that the former must have a type that may interpreted as either true or
false. Here the usual C convention is followed, in which a nonāzero value is considered true. This would include
nonāempty strings and nonāempty references to nodes, edges, etc. However, if a string can be converted to an integer,
this value is used.
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 graphābased 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 cppātype 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 supplied, objects of all types can be used as subscripts. As in C, variables and arrays must be
declared. In particular, an undeclared variable 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 inā
dex in the specified array and then the associated statement is evaluated. For numeric and string indices, the inā
dices 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.
gvpr will attempt to use an expression as a string or numeric value as appropriate. Both C-like casts and function
templates will cause conversions to be performed, if possible.
Expressions of graphical type (i.e., graph_t, node_t, edge_t, obj_t) may be followed by a field reference in the form
of .name. The resulting value is the value of the attribute named name of the given object. In addition, in certain
contexts an undeclared, unmodified identifier is taken to be an attribute name. Specifically, such identifiers denote
attributes of the current node or edge, respectively, in N and E clauses, and the current graph in BEG_G and END_G
clauses.
As usual in the libcgraph(3) model, attributes are stringāvalued. In addition, gvpr supports certain pseudoāattribā
utes of graph objects, not necessarily stringāvalued. 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 "[]",
where is "->" or "--" depending on whether the graph is directed or not. The bracket part []
only appears if the edge has a nonātrivial key.
indegree : int
the indegree of a node.
outdegree : int
the outdegree of a node.
degree : int
the degree of a node.
X : double
the X coordinate of a node. (Assumes the node has a pos attribute.)
Y : double
the Y coordinate of a node. (Assumes the node has a pos attribute.)
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 (nonāzero) if the graph is directed
strict : int
true (nonāzero) if the graph is strict
BUILTāIN 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 interpretation undirected, directed, strict, and nonāstrict, respectively. If t is empty, a
directed, nonāstrict graph is generated.
subg(g : graph_t, s : string) : graph_t
creates a subgraph in graph g with name s. If the subgraph already exists, it is returned.
isSubg(g : graph_t, s : string) : graph_t
returns the subgraph in graph g with name s, if it exists, or NULL otherwise.
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(g : 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 sg. 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 reā
turned.
isSubnode(sg : graph_t, n : node_t) : int
returns non-zero if node n is in (sub)graph sg, or zero otherwise.
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.
rename(n : node_t, newname : string) : int
changes the name of n to newname and returns 0 on success or -1 if there is an existing node with that name.
Edges
edge(t : node_t, h : node_t, s : string) : edge_t
creates an edge with tail node t, head node h and name s in the root graph. If the graph is undirected, the
distinction between head and tail nodes is unimportant. If such an edge already exists, it is returned.
edge_sg(sg : graph_t, t : node_t, h : node_t, s : string) : edge_t
creates an edge with tail node t, head node h and name s in (sub)graph sg (and all parent graphs). If the
graph is undirected, the distinction between head and tail nodes is unimportant. If such an edge already exā
ists, it is returned.
subedge(g : graph_t, e : edge_t) : 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 beā
tween head and tail nodes is unimportant. If such an edge exists, it is returned. Otherwise, NULL is reā
turned.
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(sg : graph_t, e : edge_t) : int
returns non-zero if edge e is in (sub)graph sg, or zero otherwise.
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, n : node_t) : edge_t
returns the next edge after e in the root graph.
nxtedge_sg(sg : graph_t, e : edge_t, n : node_t) : edge_t
returns the next edge after e in the graph sg.
opp(e : edge_t, n : node_t) : node_t
returns the node on the edge e not equal to n. Returns NULL if n is not a node of e. This can be useful when
using fstedge and nxtedge to enumerate the neighbors of n.
Graph I/O
write(g : graph_t) : void
prints g in dot format onto the output stream.
writeG(g : graph_t, fname : string) : void
prints g in dot format into the file fname.
fwriteG(g : graph_t, fd : int) : void
prints g in dot format onto the open stream denoted by the integer 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 subā
graph, 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 created 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 implicitly
cloned. If a graph is cloned, all nodes, edges and subgraphs 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 nodeāinduced subgraph extension in its root graph.
hasAttr(src : obj_t, name : string) : int
returns non-zero if object src has an attribute whose name is name. It returns 0 otherwise.
isAttr(g : graph_t, kind : string, name : string) : int
returns non-zero if an attribute name has been defined in g for objects of the given kind. For nodes, edges,
and graphs, kind should be "N", "E", and "G", respectively. It returns 0 otherwise.
aget(src : obj_t, name : string) : string
returns the value of attribute name in object src. This is useful 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, nonāzero 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, nonāzero on failure. See getDā
flt 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 arguā
ment 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 conā
tains 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", respecā
tively.
lock(g : graph_t, v : int) : int
implements graph locking on root graphs. If the integer v is positive, the graph is set so that future calls
to delete have no immediate effect. If v is zero, the graph is unlocked. If there has been a call to delete
the graph while it was locked, the graph is closed. If v is negative, nothing is done. In all cases, the
previous lock value is returned.
Strings
sprintf(fmt : string, ...) : string
returns the string resulting from formatting the values of the expressions occurring after fmt according to
the printf(3) format fmt
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. Simiā
larly, 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 leftmost (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 leftmost 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.
html(g : graph_t, s : string) : string
returns a ``magic'' version of s as an HTML string. This will typically be used to attach an HTML-like label
to a graph object. Note that the returned string lives in g. In particular, it will be freed when g is closed,
and to act as an HTML string, it has to be used with an object of g. In addition, note that the angle bracket
quotes should not be part of s. These will be added if g is written in concrete DOT format.
ishtml(s : string) : int
returns non-zero if and only if s is an HTML string.
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 nuā
meric.
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 adā
dresses following fmt, addresses having the form &v, where v is some declared variable of the correct type.
Returns the number of items successfully 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 containing 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 have int as its
index type. 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 argument in turn onto stdout, followed by a newline.
printf(fmt : string, ...) : int
printf(fd : int, fmt : string, ...) : int
prints the string resulting from formatting the values of the expressions following fmt according to the
printf(3) format fmt. Returns 0 on success. By default, it prints on stdout. If the optional integer fd is
given, output is written on the open stream associated with fd.
scanf(fmt : string, ...) : int
scanf(fd : int, fmt : string, ...) : int
scans in values from an input stream according to the scanf(3) format fmt. The values are stored in the adā
dresses 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 asā
sociated with fd. Returns the number of items successfully scanned.
openF(s : string, t : string) : int
opens the file s as an I/O stream. The string argument t specifies 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 sucā
cess.
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 character 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.
Associative Arrays
# arr : int
returns the number of elements in the array arr.
idx in arr : int
returns 1 if a value has been set for index idx in the array arr. It returns 0 otherwise.
unset(v : array, idx) : int
removes the item indexed by idx. It returns 1 if the item existed, 0 otherwise.
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 pseudoārandom double between 0 and 1.
srand() : int
srand(v : int) : int
sets a seed for the random number generator. The optional argument gives the seed; if it is omitted, the curā
rent 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 argument should be a color in one of the recognized
string representations. The fmt value should be one of "RGB", "RGBA", "HSV", or "HSVA". An empty string is
returned on error.
BUILTāIN VARIABLES
gvpr provides certain special, builtāin variables, whose values are set automatically by gvpr depending on the conā
text. 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 current 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
denotes the output graph. Before graph traversal, it is initialized to the target graph. After traversal and
any END_G actions, if it refers to a nonāempty graph, that graph is printed onto the output stream. It is
only valid in N, E and END_G clauses. The output graph may be set by the user.
$T : graph_t
denotes the current target graph. It is a subgraph of $G and is available only in N, E and END_G clauses.
$tgtname : string
denotes the name of the target graph. By default, it is set to "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) depthāfirst or breadthāfirst 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, see
$tvnext below.
$tvnext : node_t
indicates the next starting node for a (directed or undirected) depthāfirst or breadthāfirst 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 beginā
ning of a traversal, 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 prefix "TV_" deā
scribed 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 traversals, such as TV_fwd, requiring directed edges.
ARGC : int
denotes the number of arguments specified by the -a args commandāline argument.
ARGV : string array
denotes the array of arguments specified by the -a args commandāline argument. The ith argument is given by
ARGV[i].
BUILTāIN 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 seemingly arbitrary order.
TV_ne : tvtype_t
a traversal which first visits all of the nodes, then all of the edges.
TV_en : tvtype_t
a traversal which first visits all of the edges, then all of the nodes.
TV_dfs : tvtype_t
TV_postdfs : tvtype_t
TV_prepostdfs : tvtype_t
a traversal of the graph using a depthāfirst search on the underlying undirected graph. To do the traversal,
gvpr will check the value of $tvroot. If this has the same value that it had previously (at the start, the
previous value is initialized to NULL.), gvpr will simply look for some unvisited node and traverse its conā
nected 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 traversal will stop. Note that using TV_dfs and
$tvroot, it is possible 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 visā
ited 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 depthāfirst search on the graph following only forward arcs. The choice of
roots for the traversal is the same as described for TV_dfs above. The different order of visitation speciā
fied by TV_fwd, TV_postfwd and TV_prepostfwd are the same as those specified by the analogous traversals
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 depthāfirst search on the graph following only reverse arcs. The choice of
roots for the traversal is the same as described for TV_dfs above. The different order of visitation speciā
fied by TV_rev, TV_postrev and TV_prepostrev are the same as those specified by the analogous traversals
TV_dfs, TV_postdfs and TV_prepostdfs.
TV_bfs : tvtype_t
A traversal of the graph using a breadthāfirst search on the graph ignoring edge directions. See the item on
TV_dfs above for the role of $tvroot.
EXAMPLES
gvpr -i 'N[color=="blue"]' file.gv
Generate the nodeāinduced subgraph of all nodes with color blue.
gvpr -c 'N[color=="blue"]{color = "red"}' file.gv
Make all blue nodes red.
BEGIN { int n, e; int tot_n = 0; int tot_e = 0; }
BEG_G {
n = nNodes($G);
e = nEdges($G);
printf ("%d nodes %d edges %s\n", n, e, $G.name);
tot_n += n;
tot_e += e;
}
END { printf ("%d nodes %d edges total\n", tot_n, tot_e) }
Version of the program gc.
BEG_G { graph_t g = graph ("merge", "S"); }
E {
node_t h = clone(g,$.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
Colonāseparated list of directories to be searched to find the file specified by the -f option. gvpr has a deā
fault 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. Otherwise, GVPRPATH is used for the list.
On Windows systems, replace ``colon'' with ``semicolon'' in the previous paragraph.
BUGS AND WARNINGS
Scripts should be careful deleting nodes during N{} and E{} blocks using BFS and DFS traversals as these rely on
stacks and queues of nodes.
When the program is given as a command line argument, the usual shell interpretation takes place, which may affect
some of the special names 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 necessary, as a single backslash will be lost when the string is originally 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 funcā
tions 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 preferable for scope to reā
flect 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
SEE ALSO
awk(1), gc(1), dot(1), nop(1), expr(3), cgraph(3)
29 August 2013 GVPR(1)