The main duty of FreeCOM is to prompt the user to enter commands, which are interpreted, processed directly by FreeCOM or executed as executable files.
Those commands processed by FreeCOM directly are called Internal Commands.
Non-internal commands, which cannot be processed by FreeCOM directly, are called External Commands, because FreeCOM will search for files equally named as typed-in.
Besides to implement certain commands FreeCOM offers some features.
If present, the first non-option argument specifies the location in which
FreeCOM resides. This location is later stored in the environment variable
COMSPEC. Since DOS3+ this option is no longer necessary to find the shell
invoked during the boot process, but it may be used to let the system boot
a primary shell from one location, but use a shell of the same version from
a different location later on.
One shallt not point to a RAMdisk at this time, because FreeCOM needs to reload
certain information relatively early during execution, before AUTOEXEC.BAT had
been executed, in which, normally, FreeCOM is copied into the RAMdisk.
For convinience FreeCOM checks, if at the given location a FreeCOM exists
and is accessable, if not, the given location is ignored.
Also, the standard requires to specify a path only, but FreeCOM accepts
an absolute filename, so accepting that FreeCOM is not necessarily named
COMMAND.COM.
The second non-option argument, if present, specifies the console FreeCOM shall enable. This setting is system-wide and is not limited to FreeCOM or just this particular process tree. In its result, this argument is identical to the CTTY command.
FreeCOM knows the following options:
FreeCOM uses a number of environment variables for its own purpose.
There are a number of automatic variables that do not follow the above mentioned syntax and which contents is automatically generated. Unlike the normal variables these automatic variables are constructed of exactly two characters, the first one is a single percent sign and the second one the variable identifier:
Because automatic variables have one percent sign only, it sometimes lead to
confusion within the FOR command, e.g. in:
SET adam=eva
FOR %a in (*.*) DO echo %adam% %a
%adam is interpreted as [%a]dam.
The synopsises of the internal commands are described in a style derived from EBNF.
In interactive mode FreeCOM prompts the user to enter a command, the line is interpreted, parsed and, finally, either rejected because of an error or executed.
The first optional ? must not be mixed up with the command ?!
The colon marks the line as label, which causes to let FreeCOM ignore the line completely as no interpretation is tried on this line, neiter are any redirections created.
The ? forces FreeCOM to enable the trace mode for this line. In trace mode FreeCOM prompts the user wether to execute the resulting command.
The optional @ disables the echo status for this line. If the echo status is enabled, the line is displayed right before it is executed; see ECHO for more details.
If commands are chained with the | symbols, those commands are to be executed
as a pipe. For instance the command line:
cmd1 | cmd2 | cmd3
forms a pipe consisting of the three individual commands cmd1, cmd2, and
cmd3, where the standard output stream of cmd1 is connected to the
standard input stream of cmd2 and the output of cmd2 to the input
of cmd3. Note: Because DOS is no multitasking environment, pipes are
simulated with file and the three-command pipe will look like this:
cmd1 >%TEMP%\cmd###1.tmp
cmd2 <%TEMP%\cmd###1.tmp >%TEMP%\cmd###2.tmp
cmd3 <%TEMP%\cmd###2.tmp
The files are temporary ones and will be removed as soon as they are
no longer required, meaning the tempfile #1 is removed after cmd2
terminates and tempfile #2 upon termination of cmd3.
Redirections tie the standard input or output stream to a file or device,
for instance:
cmd arg
redirects the standard input stream of cmd to the file infile and the
standard output stream to outfile. The double output redirection specifies to append
to an existing file rather than overwriting it.
If the echo state is enabled, the user is prompted with the PROMPT string; otherwise no visible or audible prompt is issued to indicate an user activity request.
In either mode the ENTER key terminates the editing and lets FreeCOM start to interprete the entered line.
The standard input mode does neither support command line
history, except the last command line in some circumstances, nor file completion.
The following keys have a special meaning:
| Key | Meaning |
|---|---|
| F1 | Get next character from last line, if available |
| F3 | Get last line, if available |
| F5 | Place current line in last-line buffer and restart editing on a blank line |
| F6 | Insert the pseudo-character End-of-file |
| backspace | delete character to the left |
| cursor left | delete character to the left |
| cursor right | Get next character from last line, if available |
The enhanced input mode does support command line history and
file completion. The following keys have a special meaning:
| Key | Meaning |
|---|---|
| F1 | Get next character from last line, if available |
| F3 | Get last line, if available |
| F5 | Place current line in last-line buffer and restart editing on a blank line |
| backspace | delete character to the left |
| cursor down | Replace the current input line with the previous line from the history |
| cursor left | move cursor one character one position to the left |
| cursor right | Move cursor one position to the right; at the end of the line get next character from last line, if available |
| cursor up | Replace the current input line with the next line from the history |
| delete | Deletes the character on the cursor |
| end | Moves the cursor to the end of the line |
| ESC | Clear current line |
| home | moves the cursor to the beginning of the line |
| insert | Switch between insert and overwrite mode |
| TAB | Take the current word for a file and try to complete it |
| ^C | Clear current line and enable echo state. The echo state is enabled to ensure the user gets to know he is on the command line of FreeCOM rather than stuck in a non-interruptable program. |
cvs -z6 co freecomdownloads the MAIN trunk, also called HEAD, of FreeCOM.
However, CVS allows branch the development of a module at some point from the main trunk into side trees. On these branches the module can be developed further, new features can be added etc., without disturbing the main trunk (and therefore the primary release) of the module. When the side development proved its worthiness, the changes are merged into the main trunk and, hence, becomes part of the primary release.
Branches are marked by tags, though, unlike normal tags branch tags automatically
evolve with the file, what means that when a file from a specific branch is updated,
the branch tag automatically move from the current version of the file to the new one.
To check out a branch, create a new directory, change within it and execute:
cvs -z6 co -r tag freecom, where tag is the name of the branch you want to download. Note: It is not advisable to use the same directory to manage files for two different branches.
The FreeCOM module has the following active branches:
| Tag | Meaning |
|---|---|
| expExec | Stack-based execution context implementation |
| expSpawn | Module based FreeCOM, bases on expRes branch |
The FreeCOM module has the following obsoleted branches:
| Tag | Meaning |
|---|---|
| expRes | Resource management implementation.
Finally merged into trunk as of 2001/03/10 |
| Name | Meaning | Example |
|---|---|---|
| terminal | characters to be enterred on command line or displayed by the computer;EBNF: "terminal symbols" | ECHO |
| 'string' | The quotes remove the metafunction of the enclosed characters in order to specify EBNF operators as terminal symbols. EBNF: "terminal symbols" | '|' |
| bold | operators that constructs portions together; EBNF: "operators" | | |
| italian | placeholders for arguments, which are explained in the description; EBNF: "non-terminal symbols" | varname |
| Symbol | Meaning |
|---|---|
| | | alternative; use either left or right token |
| () | parenthizes enclose tokens limiting the range of | |
| [] | brackets enclose optional tokens, thus, they may appear zero or one time; they also limit the range of | |
| {} | curly brackets enclose repitive tokens, which may appear one or more times; they also limit the range of | |
| { : } | as the normal curly brackets, but any repitive tokens are delimited
by the token(s) right of the colon; for instance:
{ file : '+' }is the same as: file [{ '+' file }]and applies to:
|
| « » | is a placeholder for an arbitary string of terminal symbols, which further syntax is described by the enclosed text in English natural language. |
| ::= | assigns a meaning (right side) to a non-terminal symbol (left side);
for instanceDIR [ { option | filespec } ] option ::= / ( A | B | C )Any occurance -- only one here -- of option on the right side of an ::= or where no ::= is present at all is to be replaced by the right side of option::=. |
Unless modified by above mentioned operators a sequence of tokens specifies
that each token must be present exactly one time in exactly that order.
Note: For the sake of clearness, spaces are inserted between tokens. These
spaces do not mean that a space is allowed at this place!
Also, the fact that no _ is present does not mean that
at this place is none allowed. It is assumed that the reader will find
the places where optional spaces are valid either by "doing" or by reading the
examples.
Copyright 2000-2001 © Steffen Kaiser - current maintainer of FreeCOM