The fcsh (Flex Compiler Shell) utility provides a shell environment that you use to compile Flex applications, modules, and component libraries. It works very similarly to the mxmlc and compc command line compilers, but it compiles faster than the mxmlc and compc command-line compilers. One reason is that by keeping everything in memory, fcsh eliminates the overhead of launching the JVM and loading the compiler classes. Another reason is that compilation results (for example, type information) can be kept in memory for subsequent compilations.

This utility is intended to improve the experience of users of the command-line compilers. If you are using Flex Builder, you do not need to use fcsh. The Flex Builder tool already uses the optimizations provided by fcsh.

For simple applications, fcsh might not be necessary. But for more complex applications that you compile frequently, you should experience a significant performance improvement over using the mxmlc and compc command-line compilers.

When you first compile an application with fcsh, you will not typically notice any difference in speed between the fcsh and the command-line compilers. This is because fcsh must load the application model and custom libraries into memory, just as the command-line compilers would. After that, however, each subsequent compilation uses the libraries in memory to compile. This reduces the amount of disk access that the compilers need to perform and should result in shorter compile times.

The fcsh tool is in the bin directory. For Unix and Mac OS, it is a shell script called fcsh. For Windows, it is fcsh.exe. You invoke it only from the command line. The Java settings are managed by the jvm.config file in the bin directory.

Using fcsh

You invoke fcsh from the command line. You can launch the utility either as an executable (Windows) or shell command (Unix/Linux/Mac).

1. Open a command prompt.
2. Navigate to the {SDK_root}/bin directory.
3. Enter fcsh at the command line. Your commands will now be executed within the fcsh environment. You will know this if the (fcsh).

Typically, you compile a simple application when you first launch fcsh; for example:

(fcsh) mxmlc c:/myfiles/MyApp.mxml

The fcsh utility returns a target id:

fcsh: Assigned 1 as the compile target id.

You then refer to the target ids when using subsequent commands inside the fcsh utility. For example, to compile the application with incremental compilation:

(fcsh) compile 1

You can enter help in the fcsh shell to see a list of available options; for example:

(fcsh) help

You can enter quit in the fcsh shell to exit fcsh and return to the command prompt; for example:

(fcsh) quit

The following example shows that fcsh dramatically reduces compilation time when compiling the same application multiple times:

(fcsh) mxmlc -benchmark=true flexstore.mxml
    Total time: 8885ms
    Peak memory usage: 84 MB (Heap: 58, Non-Heap: 26)
(fcsh) mxmlc -benchmark=true flexstore.mxml
    Total time: 5140ms
    Peak memory usage: 84 MB (Heap: 57, Non-Heap: 27)

Then, the second full compilation of the same application is much faster:

> touch flexstore.mxml

(fcsh) compile 1
    Files changed: 1 Files affected: 0
    Total time: 933ms
    Peak memory usage: 88 MB (Heap: 62, Non-Heap: 26)
    flexstore.swf (522456 bytes)
    Total time: 1102ms
    Peak memory usage: 77 MB (Heap: 51, Non-Heap: 26)
(fcsh)

About fcsh options

The following table describes the available fcsh options: