console.md

Simple console command

You can check VCL behavior without VCL file in repl of falco console.

Usage

falco console -h
=========================================================
    ____        __
   / __/______ / /_____ ____
  / /_ / __  // //  __// __ \
 / __// /_/ // // /__ / /_/ /
/_/   \____//_/ \___/ \____/  Fastly VCL developer tool

=========================================================
Usage:
    falco console [flags]

Flags:
    -s, --scope : Define initial scope
    -h, --help  : Show this help

Run console with fetch scope example:
    falco console -s fetch

Control Commands

In console, some control commands that start with \ are enabled.

Command	Desctiption
\s, \scope [scope]	Change input evaluation scope (recv, fetch, deliver, etc...)
\h, \help	Show this help
\q, \quit	Quit console

Console Behavior

The console does single-line code evaluatation and must be valid of VCL syntax. And some predefined variables depends on the scope, then you can change artibrary scope by typing the \s command:

@RECV>> \s FETCH

Now you can switch to the fetch scope.

Evaluation

falco evaluates input as statement and expression, it means you cannot declare backend, subroutine - of root declarations. By inputting set statement, falco can store the value in this session. Of course declare local var.XXX statement also available.

If you want to see the variable value, type variable as expression:

@RECV>> set req.http.Foo = "bar";
@RECV>> req.http.Foo;
(STRING)bar

Falco evaluates expression and display value with its type.

Note that console runtime uses interpreter, therefore the result depends on the intepreter implementation.