cheat sheets.

Undirected graphs

graph graphname {
  a -- b -- c;
  b -- d;
}

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Directed graphs

digraph graphname {
  a -> b -> c;
  b -> d;
}

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Attributes

graph graphname {
  // The label attribute can be used to change the label of a node
  a [label="Foo"];
  // Here, the node shape is changed.
  b [shape=box];
  // These edges both have different line properties
  a -- b -- c [color=blue];
  b -- d [style=dotted];
}

More attributes:
http://www.graphviz.org/doc/schema/attributes.xml

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Comments

 // This is a single line comment.
 /* This is a
    multiple line
    comment. */
 # Lines like this are also ignored.