A Channel implements low-level input/output for the AST library. Writing an Object to a Channel (using AST_WRITE) will generate a textual representation of that Object, and reading from a Channel (using AST_READ) will create a new Object from its textual representation.
Normally, when you use a Channel, you should provide "source" and "sink" routines which connect it to an external data store by reading and writing the resulting text. By default, however, a Channel will read from standard input and write to standard output.
If the null routine AST_NULL is suppied as the SOURCE value, the Channel will read from standard input instead.
If the null routine AST_NULL is suppied as the SINK value, the Channel will write to standard output instead.
AST A Library for Handling World Coordinate Systems in Astronomy