---
name: "gv_tcl"
section: "3"
platform: "linux"
package: "libgv-tcl"
version: "2.20.2-3"
release: "Debian 5.0 (Lenny)"
platforms: ["linux"]
url: "https://new.carta.tech/gv_tcl"
---

# gv\_tcl(3)

graph manipulation in tcl

## NAME

gv\_tcl - graph manipulation in tcl

## SYNOPSIS

\#!/usr/bin/tclsh\
 package require gv

## USAGE

Requires tcl8.3 or later.

## INTRODUCTION

**gv\_tcl** is a dynamically loaded extension for **tcl** that provides access to the graph facilities of **graphviz.**

## COMMANDS

- **New graphs**

  - New empty graph

  *\<graph\_handle\>* **gv::graph** *\<name\>*\
   *\<graph\_handle\>* **gv::digraph** *\<name\>*\
   *\<graph\_handle\>* **gv::strictgraph** *\<name\>*\
   *\<graph\_handle\>* **gv::strictdigraph** *\<name\>*\

- New graph from a dot-syntax string or file

  *\<graph\_handle\>* **gv::readstring** *\<string\>*\
   *\<graph\_handle\>* **gv::read** *\<filename\>*\
   *\<graph\_handle\>* **gv::read** *\<channel\>*\

- Add new subgraph to existing graph

  *\<graph\_handle\>* **gv::graph** *\<graph\_handle\> \<name\>*\

- **New nodes**

  - Add new node to existing graph

  *\<node\_handle\>* **gv::node** *\<graph\_handle\> \<name\>*\

- **New edges**

  - Add new edge between existing nodes

  *\<edge\_handle\>* **gv::edge** *\<tail\_node\_handle\> \<head\_node\_handle\>*\

- Add a new edge between an existing tail node, and a named head node which will be induced in the graph if it doesn't already exist

  *\<edge\_handle\>* **gv::edge** *\<tail\_node\_handle\> \<head\_name\>*\

- Add a new edge between an existing head node, and a named tail node which will be induced in the graph if it doesn't already exist

  *\<edge\_handle\>* **gv::edge** *\<tail\_name\> \<head\_node\_handle\>*\

- Add a new edge between named tail and head nodes which will be induced in the graph if they don't already exist

  *\<edge\_handle\>* **gv::edge** *\<graph\_handle\> \<tail\_name\> \<head\_name\>*\

- **Setting attribute values**

  - Set value of named attribute of graph/node/edge - creating attribute if necessary

  *\<string\>* **gv::setv** *\<graph\_handle\> \<attr\_name\> \<attr\_value\>*\
   *\<string\>* **gv::setv** *\<node\_handle\> \<attr\_name\> \<attr\_value\>*\
   *\<string\>* **gv::setv** *\<edge\_handle\> \<attr\_name\> \<attr\_value\>*\

- Set value of existing attribute of graph/node/edge (using attribute handle)

  *\<string\>* **gv::setv** *\<graph\_handle\> \<attr\_handle\> \<attr\_value\>*\
   *\<string\>* **gv::setv** *\<node\_handle\> \<attr\_handle\> \<attr\_value\>*\
   *\<string\>* **gv::setv** *\<edge\_handle\> \<attr\_handle\> \<attr\_value\>*\

- **Getting attribute values**

  - Get value of named attribute of graph/node/edge

  *\<string\>* **gv::getv** *\<graph\_handle\> \<attr\_name\>*\
   *\<string\>* **gv::getv** *\<node\_handle\> \<attr\_name\>*\
   *\<string\>* **gv::getv** *\<edge\_handle\> \<attr\_name\>*\

- Get value of attribute of graph/node/edge (using attribute handle)

  *\<string\>* **gv::getv** *\<graph\_handle\> \<attr\_handle\>*\
   *\<string\>* **gv::getv** *\<node\_handle\> \<attr\_handle\>*\
   *\<string\>* **gv::getv** *\<edge\_handle\> \<attr\_handle\>*\

- **Obtain names from handles**

  *\<string\>* **gv::nameof** *\<graph\_handle\>*\
   *\<string\>* **gv::nameof** *\<node\_handle\>*\
   *\<string\>* **gv::nameof** *\<attr\_handle\>*\

- **Find handles from names**

  *\<graph\_handle\>* **gv::findsubg** *\<graph\_handle\> \<name\>*\
   *\<node\_handle\>* **gv::findnode** *\<graph\_handle\> \<name\>*\
   *\<edge\_handle\>* **gv::findedge** *\<tail\_node\_handle\> \<head\_node\_handle\>*\
   *\<attr\_handle\>* **gv::findattr** *\<graph\_handle\> \<name\>*\
   *\<attr\_handle\>* **gv::findattr** *\<node\_handle\> \<name\>*\
   *\<attr\_handle\>* **gv::findattr** *\<edge\_handle\> \<name\>*\

- **Misc graph navigators returning handles**

  *\<node\_handle\>* **gv::headof** *\<edge\_handle\>*\
   *\<node\_handle\>* **gv::tailof** *\<edge\_handle\>*\
   *\<graph\_handle\>* **gv::graphof** *\<graph\_handle\>*\
   *\<graph\_handle\>* **gv::graphof** *\<edge\_handle\>*\
   *\<graph\_handle\>* **gv::graphof** *\<node\_handle\>*\
   *\<graph\_handle\>* **gv::rootof** *\<graph\_handle\>*\

- **Obtain handles of proto node/edge for setting default attribute values**

  *\<node\_handle\>* **gv::protonode** *\<graph\_handle\>*\
   *\<edge\_handle\>* **gv::protoedge** *\<graph\_handle\>*\

- **Iterators**

  - Iteration termination tests

  *\<boolean\_string\>* **gv::ok** *\<graph\_handle\>*\
   *\<boolean\_string\>* **gv::ok** *\<node\_handle\>*\
   *\<boolean\_string\>* **gv::ok** *\<edge\_handle\>*\
   *\<boolean\_string\>* **gv::ok** *\<attr\_handle\>*\

- Iterate over subgraphs of a graph

  *\<graph\_handle\>* **gv::firstsubg** *\<graph\_handle\>*\
   *\<graph\_handle\>* **gv::nextsubg** *\<graph\_handle\> \<subgraph\_handle\>*\

- Iterate over supergraphs of a graph (obscure and rarely useful)

  *\<graph\_handle\>* **gv::firstsupg** *\<graph\_handle\>*\
   *\<graph\_handle\>* **gv::nextsupg** *\<graph\_handle\> \<subgraph\_handle\>*\

- Iterate over edges of a graph

  *\<edge\_handle\>* **gv::firstedge** *\<graph\_handle\>*\
   *\<edge\_handle\>* **gv::nextedge** *\<graph\_handle\> \<edge\_handle\>*\

- Iterate over outedges of a graph

  *\<edge\_handle\>* **gv::firstout** *\<graph\_handle\>*\
   *\<edge\_handle\>* **gv::nextout** *\<graph\_handle\> \<edge\_handle\>*\

- Iterate over edges of a node

  *\<edge\_handle\>* **gv::firstedge** *\<node\_handle\>*\
   *\<edge\_handle\>* **gv::nextedge** *\<node\_handle\> \<edge\_handle\>*\

- Iterate over out-edges of a node

  *\<edge\_handle\>* **gv::firstout** *\<node\_handle\>*\
   *\<edge\_handle\>* **gv::nextout** *\<node\_handle\> \<edge\_handle\>*\

- Iterate over head nodes reachable from out-edges of a node

  *\<node\_handle\>* **gv::firsthead** *\<node\_handle\>*\
   *\<node\_handle\>* **gv::nexthead** *\<node\_handle\> \<head\_node\_handle\>*\

- Iterate over in-edges of a graph

  *\<edge\_handle\>* **gv::firstin** *\<graph\_handle\>*\
   *\<edge\_handle\>* **gv::nextin** *\<node\_handle\> \<edge\_handle\>*\

- Iterate over in-edges of a node

  *\<edge\_handle\>* **gv::firstin** *\<node\_handle\>*\
   *\<edge\_handle\>* **gv::nextin** *\<graph\_handle\> \<edge\_handle\>*\

- Iterate over tail nodes reachable from in-edges of a node

  *\<node\_handle\>* **gv::firsttail** *\<node\_handle\>*\
   *\<node\_handle\>* **gv::nexttail** *\<node\_handle\> \<tail\_node\_handle\>*\

- Iterate over nodes of a graph

  *\<node\_handle\>* **gv::firstnode** *\<graph\_handle\>*\
   *\<node\_handle\>* **gv::nextnode** *\<graph\_handle\> \<node\_handle\>*\

- Iterate over nodes of an edge

  *\<node\_handle\>* **gv::firstnode** *\<edge\_handle\>*\
   *\<node\_handle\>* **gv::nextnode** *\<edge\_handle\> \<node\_handle\>*\

- Iterate over attributes of a graph

  *\<attr\_handle\>* **gv::firstattr** *\<graph\_handle\>*\
   *\<attr\_handle\>* **gv::nextattr** *\<graph\_handle\> \<attr\_handle\>*\

- Iterate over attributes of an edge

  *\<attr\_handle\>* **gv::firstattr** *\<edge\_handle\>*\
   *\<attr\_handle\>* **gv::nextattr** *\<edge\_handle\> \<attr\_handle\>*\

- Iterate over attributes of a node

  *\<attr\_handle\>* **gv::firstattr** *\<node\_handle\>*\
   *\<attr\_handle\>* **gv::nextattr** *\<node\_handle\> \<attr\_handle\>*\

- **Remove graph objects**

  *\<boolean\_string\>* **gv::rm** *\<graph\_handle\>*\
   *\<boolean\_string\>* **gv::rm** *\<node\_handle\>*\
   *\<boolean\_string\>* **gv::rm** *\<edge\_handle\>*\

- **Layout**

  - Annotate a graph with layout attributes and values using a specific layout engine

  *\<boolean\_string\>* **gv::layout** *\<graph\_handle\> \<engine\>*\

- **Render**

  - Render a layout into attributes of the graph

  *\<boolean\_string\>* **gv::render** *\<graph\_handle\>*\

- Render a layout in a specific format

  *\<boolean\_string\>* **gv::render** *\<graph\_handle\> \<format\>*\
   *\<boolean\_string\>* **gv::render** *\<graph\_handle\> \<format\> \<filename\>*\
   *\<boolean\_string\>* **gv::render** *\<graph\_handle\> \<format\> \<channel\>*\
   *\<string\>* **gv::renderdata** *\<graph\_handle\> \<format\>*\

- Writing graph back to file

  *\<boolean\_string\>* **gv::write** *\<graph\_handle\> \<filename\>*\
   *\<boolean\_string\>* **gv::write** *\<graph\_handle\> \<channel\>*\

## KEYWORDS

graph, dot, neato, fdp, circo, twopi, tcl.