Exploring Expect

Adding Extensions To Expect

You can add other extensions to Expect similarly to the way I described adding extensions to tclsh. However, by adding extensions to Expect, you keep aspects of Expect, such as Expect’s command-line argument handling.

The Expect source directory contains the template for Expect in exp_main_exp.c. Copy this file to a new directory and look inside it at the main function. You will find the statements (not necessarily in this order):

if (Tcl_Init(interp) == TCL_ERROR) {
    return TCL_ERROR;
}
if (Exp_Init(interp) == TCL_ERROR) {
    return TCL_ERROR;
}

Most other extensions can be added by calling XXX_Init, where XXX is the extension prefix. The actual call should look similar to the ones for Tcl and Expect.

You can generally put the other XXX_Init calls in any order unless the extensions attempt to use the same command names. In that case, the later extensions “win”. Note that the basic Tcl commands are created before Tcl_Init. Other XXX_Init functions generally define commands for each extension themselves.

Add any include lines near the top of the file (anywhere after the include of "tcl.h“) as appropriate to your extension.

Compile the exp_main_exp.c file with the following command.

cc -I/usr/local/include exp_main_exp.c ... \
      -L/usr/local/lib -lexpect -ltcl -lm

You may need to adjust this command depending on your installation. The −i flag describes the directory where the include files of Tcl, Expect, and other extensions live. Similarly, the -L flag lists where ...