Tornado

Tornado 2.0
User’s Guide
shell of its location; the shell then issues the requests to actually copy the string to
that memory. This request reaches the agent on the target, and it writes the 14 bytes
(including the terminating null) there.
The shell’s C-expression interpreter must now determine what the name opendir
represents. Because opendir( ) is not one of the shell’s own commands, the shell
looks up the symbol (through the target server) in the symbol table.
The C interpreter now needs to evaluate the function call to opendir( ) with the
particular argument specified, now represented by a memory location on the
target. It instructs the agent (through the server) to spawn a task on the target for
that purpose, and awaits the result.
As before, the C interpreter looks up a symbol name (dir) through the target server;
when the name turns out to be undefined, it instructs the target server to allocate
storage for a new int and to make an entry pointing to it with the name dir in the
symbol table. Again these symbol-table manipulations take place entirely on the
host.
The interpreter now has an address (in target memory) corresponding to dir, on the
left of the assignment statement; and it has the value returned by opendir( ), on the
right of the assignment statement. It instructs the agent (again, through the server)
to record the result at the dir address, and evaluation of the statement is complete.
5.8.2 Shell Components
The Tornado shell includes two interpreters, a common front end for command
entry and history, and a back end that connects the shell to the global Tornado
environment to communicate with the target server. Figure 5-3 illustrates these
components:
Line Editing
The line-editing and command history facilities are designed to be
unobtrusive, and support your access to the interpreters. 5.5 Shell Line Editing,
p.193 describes the vi-like editing and history front end.
C-Expression Interpreter
The most visible component is the C-expression interpreter, because it is the
interface that most closely resembles the application programming
environment. The bulk of this chapter describes that interpreter.
Tcl Interpreter
An interface for extending the shell or automating shell interactions, described
in 5.7 Tcl: Shell Interpretation, p.198.
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