Using the REPL
The default Chicken REPL (Read Eval Print Loop) can be accessed by executing the csi program.
$ csi CHICKEN (c)2008-2011 The Chicken Team (c)2000-2007 Felix L. Winkelmann Version 4.7.0 linux-unix-gnu-x86 [ manyargs dload ptables ] compiled 2011-05-25 on mario (Linux) #;1>
By default the REPL doesn't have some features you'd find in command line interfaces which use GNU readline library. But you can have such features by using either the readline egg or the linenoise egg.
You can also call csi using rlwrap, but the readline egg has additional features like tab-completion of function and variable names.