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https://github.com/jhpyle/mtcp

Unofficial fork of https://www.brutman.com/mTCP with terminal emulator changes
https://github.com/jhpyle/mtcp

Last synced: about 1 year ago
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Unofficial fork of https://www.brutman.com/mTCP with terminal emulator changes

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README 

          
# jhpyle/mTCP



This is an unofficial fork of the Telnet application from Michael

B. Brutman's [mTCP].  It adds:



* [Enhanced Keyboard] support

* Mouse and clipboard support

* Translation of incoming Unicode characters

* [Sixel graphics]

* Printer support



The binary is available as the [TELNET.EXE] file and the

[TELNETNU.EXE] file, which are in the [bin] directory.  The

[TELNETNU.EXE] file is the same as [TELNET.EXE] except that it

disables Unicode translation.



The fork is based on the [mTCP-src_2022-07-01.zip] version of [mTCP].



## The changes



The purpose of this repository is to expand the `ansi` terminal

emulation capabilities of [mTCP]'s Telnet application.  Where a

feature is not supported by the `ansi` standard, ideas are borrowed

from the `xterm` standard.



### Keyboard



The following keys are transmitted:



* Function keys F1-F12;

* Insert, Delete, Home, End, Page Up, Page Down;

* Cursor keys;

* Shift, Ctrl, Ctrl-shift, Alt, and Alt-Shift modifications of the above;

* Tab, Ctrl-Tab, Shift-Tab;

* Ctrl-Backspace;

* Ctrl-Space; and

* Ctrl-PrtScr.



In the official [mTCP], Page Up and Page Down scroll are not passed

through but are used for scrolling through the output history.  In

this version, that function is moved to the Alt-Page Up and Alt-Page

Down keys (or Ctrl-Page Up and Ctrl-Page Dn if the [Enhanced Keyboard]

is not available), and Page Up and Page Down are passed through to the

server.



For compatibility with [Emacs], all Alt-(key) combinations that are

not used by the Telnet application are passed through as ESC-(key).



The Delete key is passed through as `ESC [ 3 ~` instead of the default

of character 127.



Some of the above keys are not available if your computer lacks

support for the [Enhanced Keyboard].



### Mouse



Mouse support is available in two forms.



First, if the server sends back `xterm` [DECSET] signals to enable

mouse tracking, mouse activity is transmitted to the server using

`xterm` escape sequences.  [Emacs] sends these sequences when

`xterm-mouse-mode` is in use, and [Vim] sends them when `set mouse=a`

is used.  [Midnight Commander] provides mouse support if the `-x` switch

is used to enable `xterm` mode.



Second, if the [DECSET] signals are not received, mouse activity does

not result in escape sequences sent to the terminal, but the mouse can

be used for copying and pasting.  The controls are:



* Left-click and drag to select a region;

* Right-click to extend a selection;

* Double-click to select a word;

* Triple-click to select a line; and

* Middle-click to paste the selection.



Clicking the left and right mouse buttons at the same time emulates

the middle mouse button.



For mouse support to work, you may need to install a mouse driver

(typically [MOUSE.COM]) before running [TELNET.EXE] or [TELNETNU.EXE].



### Unicode



When UTF-8 characters are received, they are translated if possible

into one of the 256 characters that can be displayed in text mode.  By

default, Unicode characters are translated into [Code Page 437].  If

no translation is available, a default character, `¿`, is printed.



Unicode translation does not take place when sending outbound

characters.



If you are connected to server that sends "extended ASCII" characters

(codes greater than 127) with the expectation that your Telnet client

will display them directly to video memory (e.g., as [Code Page 437]

character), `TELNET.EXE` will misinterpret these codes as the

first byte of a Unicode sequence. Thus, you will get garbage on the

screen. If you need to to connect to a server that sends "extended

ASCII" characters, use `TELNETNU.EXE`.



The [Code Page] and the default unprintable character are

configurable in the `MTCP.CFG` file using the directives

`TELNET_UTF`, `TELNET_CODEPAGE`, and `TELNET_UTF_DEFAULT`.  For

example, the following excerpt demonstrates enabling [Code Page 737]

translation in place of the default [Code Page 437], and setting the

default character for unprintable Unicode sequences to the space

(0x20).



    TELNET_CODEPAGE 737

    TELNET_UTF_DEFAULT 0x20

    TELNET_UTF 737 0x0000 0x00

    TELNET_UTF 737 0x0001 0x01

    TELNET_UTF 737 0x0002 0x02

    TELNET_UTF 737 0x0003 0x03

    ...

    TELNET_UTF 737 0x00a0 0xff



There are complete example configurations in the [`config`] folder for

[Code Page 737], [Code Page 775], [Code Page 850], [Code Page 852],

[Code Page 855], [Code Page 857] [Code Page 860], [Code Page 861],

[Code Page 862], [Code Page 863], [Code Page 864], [Code Page 865],

[Code Page 866], [Code Page 869], and [Code Page 874].  A file is also

included for [Code Page 437] in case you want to customize the default

translation.



You can copy and paste from these files into your `MTCP.CFG` file.

The `TELNET_CODEPAGE` directive selects a code page, and any

directives beginning with `TELNET_UTF` will be used to define the

translations that are used.  The format of each line is:



    TELNET_UTF   



where `CODE_PAGE_NUMBER` is the number of the code page (e.g. 737),

the `UNICODE_NUMBER` is a hexadecimal Unicode number (e.g., `0x266a`

for the musical note character) and `CHARACTER_NUMBER` is a

hexadecimal 8-bit number representing the character on the screen

(e.g., `0x0d` for the musical note character).  Note that the

`TELNET_CODEPAGE` directive will not have any effect in the absence of

`TELNET_UTF` lines that define the translations for the code page.



For best results, sort your `TELNET_UTF` lines by the Unicode

numbers. If they are out of order, they will need to be sorted when

Telnet starts, which extends the start time.



The `TELNET_UTF_DEFAULT` directive indicates which character should be

printed if there is no translation for a particular Unicode character.

The number must be written in hexadecimal.  The default is `0xa8`,

which is the character ¿ in [Code Page 437].



If you switch between code pages, you can keep definitions for several

code pages in your `MTCP.CFG` file and change only the

`TELNET_CODEPAGE` line when you want to switch among them.



Depending on what applications you use and what content you view, you

may wish to modify the standard Unicode translations, add additional

characters, or add additional code pages.



The code page translations in the [`config`] folder were created using

translation tables available on [unicode.org].



### Graphics



If a [Sixel graphics] escape sequence is encountered, the image will

be downloaded and then displayed on the screen.  It may take

significant time for the image to download.  While the image is

downloading, the screen is unchanged; this is so that you can keep

reading what is on the screen while you wait for the graphics image to

appear.  After viewing the image, you can then press any key to get

back to text mode.



The supported graphics modes are:



* 720x348x2 - requires a [Hercules Graphics Card]

* 320x200x256 - requires [VGA] or [MCGA]

* 640x480x2 - requires [VGA] or [MCGA]

* 320x200x4 - [CGA]

* 640x200x2 - [CGA]



Telnet will use the highest resolution graphics mode available, given

the number of colors in the image.  If there are two colors, it will

use a two-color graphics mode.  If there are four colors, it will use

a 320x200x4 mode with the matching palette.



Telnet does not autodetect whether you have a [Hercules Graphics

Card], [VGA], or [MCGA].  By default, it assumes you have [VGA] or

[MCGA] and it will try to display images in the [VGA]/[MCGA] modes.



If your computer does not support the [VGA]/[MCGA] modes, you will

need to add a line to your `MTCP.CFG` file to stop it from using those

modes.  If you have a [CGA] adapter, set the following:



    TELNET_CGA 1



If you have a [Hercules Graphics Card], set the following instead:



    TELNET_HGC 1



Telnet will not do any image resizing or dithering.  If an image is

wider or taller than the graphics mode supports, then it will not

display.



For best results when connected to a Linux machine, use the included

[show] script to convert an image file to [Sixel] escape sequences.

This script calls the [`img2sixel`] command with the appropriate

parameters for resizing images and converting colors.



Without any parameters, [show] will display an image in 256 colors.



    show my_image.png



If you have the [Hercules Graphics Card], use the `--hercules` switch:



    show --hercules my_mono_image.png



If you have [CGA] graphics only, use the `--cga` switch so that color

images are reduced to four colors.



    show --cga my_image.png



By default, [show] will use the bright cyan/magenta/white palette in

`--cga` mode.  You can tell it to use a different palette with the

`--colors` switch:



    show --colors CyanMagenta my_image.png

    show --colors LightCyanMagenta my_image.png

    show --colors GreenRed my_image.png

    show --colors LightGreenRed my_image.png



To make an image display in monochrome, use the `--mono` switch:



    show --mono my_mono_image.png



By default, the `--mono` switch will shrink the image to fit in

640x480, which [VGA] and [MCGA] monitors can display.  If you have

[CGA] only, make sure to include the `--cga` switch:



    show --mono --cga my_mono_image.png



This will resize the image to fit within [CGA]'s 640x200 resolution.



With the `--me` parameter, [show] will take a picture with

`/dev/video0` and then display it:



    show --me



To see the usage instructions, call `show` with the `--help` switch.



    show --help



For instructions on installing the [show] utility and integrating it

with applications, see the Setup section below.



The [show] utility is a [bash] script, so you can edit it. You can

change the script so that you do not have to provide any flags to get

the image format you want.



### Printing



Historically, the typewriter preceded the computer, and the [first

terminals] acted like typewriters, printing characters to paper rather

than to a screen.  Early video terminals, like the [VT52] and [VT100],

supported connecting a printer to the terminal, and could switch into

a mode in which incoming characters were sent to the printer and the

user could create a "hardcopy" of the session.  When the [VT100]

terminal received `ESC [ 5 i`, all characters received thereafter

would be relayed to the attached printer.  When the terminal received

`ESC [ 4 i`, the terminal would stop relaying the characters to the

printer.  The `ansi` and `xterm` protocols incorporated this feature.



This version of [mTCP] Telnet has been modified to provide support for

this method of printing.  By default, printing is disabled, however,

so that even if the remote server sends `ESC [ 5 i`, the printer will

not print anything.  Pressing Alt-P toggles the enabling and disabling

of printing.  You can see whether printing is enabled by visiting the

help screen (Alt-H).  If printing is enabled and the remote server

sends `ESC [ 5 i`, Telnet will start sending all received characters

to the LPT1 printer.  It will continue to do so until it receives `ESC

[ 4 i`.  Characters will also be sent to the screen.



If your printer requires initialization, you can add a

`TELNET_PRINTER_INIT` line to your `MTCP.CFG` file, listing a series

of ASCII characters expressed as two-digit hexadecimal numbers

separated by commas.  For example, these are printer initialization

codes for a Diablo 630 printer.



```

TELNET_PRINTER_INIT 1b,51,0d,1b,1f,0b,1b,1e,09,1b,35

```



Up to sixteen ASCII characters can be defined using

`TELNET_PRINTER_INIT`.  These characters are sent to the printer the

first time you type Alt-P to enable printing.



This repository contains a Python script, [tprint], that can be used

to print a file or an output stream.  You can call it either as a pipe

or you can give it the name of one or more files:



    ps ax | tprint

    tprint foo.txt

    tprint foo.txt bar.txt

    tprint *.msg



In addition, this repository contains two [bash] scripts, [startprint]

and [stopprint], which echo the escape sequences for turning printing

on and off.  As explained in "Configuring your applications," below,

you can also bind keys in [bash] for turning printing on and off.



## Compatibility



This package has been tested on:



* [IBM PS/2 Model 25] with an 8086 processor running PC-DOS 4.0 and

  Microsoft Mouse Driver ([MOUSE.COM]) version 7.03.

* [IBM PC model 5150] with the [Hercules Graphics Card].



Unfortunately, I do not have access to other machines, so I do not

know what problems may arise on other systems.  Please feel free to

create GitHub issues to let me know what doesn't work.



As discussed above, you will need to add `TELNET_HGC 1` or

`TELNET_CGA 1` to your `MTCP.CFG` file if you have a [Hercules

Graphics Card] or [CGA] adapter in your system.



[EGA] is currently not supported, because I do not own an [EGA] card

or [EGA]-compatible monitor.



## Performance



This version of mTCP Telnet is not as fast as the official mTCP

Telnet, so you may see that screens do not draw as fast.



The reason for the slowness is due to the increased feature

support. In the main loop of the Telnet application, there are more

if/else statements that need to run in order to support additional

incoming escape sequences, process multi-byte Unicode sequences,

support the mouse feature, and support the printing feature.



If the server you are connected to sends UTF-8 instead of [Code Page

437] "extended ASCII" characters, it will send two or three bytes

instead of one byte to draw one character, so screen draws may appear

slower just because more bytes need to be transferred.



If you can think of ways the code can run more efficiently while

supporting the same set of features, feel free to create a GitHub pull

request.



## Setup



In order for your Telnet client and remote servers to communicate

effectively using escape sequences for colors, mouse support, and

keypresses, the remote machines will need to know the precise

capabilities of your Telnet client.  On Linux, terminal capabilites

are defined in a "terminfo" file.  The `TERM` variable in your remote

shell environment tells the remote machine which "terminfo" file to

use.  `TERM` is typically set to a value like `ansi`, `vt320`, or

`xterm`.  Terminal-based applications use the `TERM` variable to

decide what features will be enabled and how they will communicate

with you.



The Telnet client reports its terminal type as `ANSI`.  This can be

changed by setting the variable `TELNET_TERMTYPE` in the `MTCP.CFG`

file, but it is generally better to keep it as `ANSI`.  Many

terminal-based applications look at the `TERM` variable and expect it

to be set to a standard value like `xterm`, `vt100`, or `ansi`, so you

are generally better off using a standard terminal type like `ANSI`.



The `ANSI` standard is not well-defined.  There are many variants, and

the one that this Telnet uses is its own variant.  In order to use all

of the features of this Telnet's ANSI terminal emulation, you need to

create your own "terminfo" file.  This package contains the source

code for this "terminfo" file ([ansi.src]).



On every Linux machine to which you might want to connect (directly

with Telnet or indirectly with [ssh]), install the `ansi` "terminfo"

file and the [show] script.



You can do this by cloning the GitHub repository with `git` and

running `./install.sh` as root.  If you don't have `git` installed,

you can install it with `sudo apt-get install git`.



The [install.sh] script copies [show] to `/usr/local/bin`, installs

color map PNG files in `/usr/local/share/sixel`, and compiles and

installs the `ansi` "terminfo" file using `tic`.



The [show] script depends on `libsixel-bin` (for `img2sixel`),

`libimage-size-perl` (for `imgsize`), and `streamer` (for the `--me`)

option.  The installation of the `ansi` "terminfo" file depends on the

`tic` command, which is available in `ncurses-bin`.



    sudo apt-get install libsixel-bin libimage-size-perl streamer ncurses-bin

    git clone https://github.com/jhpyle/mTCP

    cd mTCP

    sudo ./install.sh

    cd ..



The names of these packages and the application for installing

packages (in this example, `apt-get`) might be different on your

machines, so you may need to revise this.



If `/usr/local/bin` is not part of your `PATH` (try `echo $PATH` to

see what your `PATH` is) you might want to edit the install script so

that it installs the `show` script elsewhere.



### Manual installation



If you want to install the [show] script manually, run commands

equivalent to the following:



    git clone https://github.com/jhpyle/mTCP

    sudo install mTCP/sixel/show /usr/local/bin

    sudo mkdir -p /usr/local/share/sixel

    sudo install -m 644 mTCP/sixel/*.png /usr/local/share/sixel



The [show] script needs to go into a directory that is in your `PATH`.

The PNG files can go in any directory, but if you put them in a

directory other than `/usr/local/share/sixel`, make sure you edit the

[show] script to change the definition of `COLORMAPS` so that it

points to the directory you are using.



To install the `ansi` "terminfo" file manually, compile the `ansi.src`

file with `tic`:



    sudo tic -x -o/etc/terminfo mTCP/ansi.src



Here, `/etc/terminfo` is the directory where custom terminfo

description files are installed.  It might be located in a different

directory on your system.



This will override the standard terminfo file that is used when the

`TERM` environment variable is set to `ansi`.



If you do not have administrator access on the machine, you can

install the terminfo description for yourself only.  You can do this

by running:



    tic -x mTCP/ansi.src



This will compile the [ansi.src] file and create the terminfo

description file `~/.terminfo/a/ansi`.



After installing the terminfo file, you can run `rm ansi.src` because

you will not need the `ansi.src` file any longer (unless you would

like to edit it).



To install the [tprint], [startprint], and [stopprint] utilities

manually, run commands equivalent to the following:



    sudo install mTCP/printing/tprint /usr/local/bin

    sudo install mTCP/printing/stopprint /usr/local/bin

    sudo install mTCP/printing/startprint /usr/local/bin



### Configuring your applications



The "terminfo" file, on its own, is not sufficient for all of your

Linux applications to work appropriately with the Telnet client.  Many

applications look at the `TERM` environment variable but bypass the

"terminfo" system.  You will need to edit the configuration files of

your applications to get the most out of Telnet.



To improve your [bash] command line experience, add this to your

`~/.inputrc` file:



    "\e[7;5~" backward-kill-word

    "\e[3;2~" delete-char

    "\e[3;5~" kill-word

    "\e[5~": beginning-of-history

    "\e[6~": end-of-history



If you don't have an `~/.inputrc` file, you can create one with just

these lines in it.  This will allow you to type Ctrl-Backspace, Delete,

Ctrl-Delete, Page Up, and Page Down on the command line.



If you use [Emacs], download [ansi.el].



    curl -o ansi.el https://github.com/jhpyle/mTCP/blob/master/ansi.el



Incorporate the contents of this file into your `.emacs` file.  This

will ensure that [Emacs] will recognize the control sequences that the

Telnet client will send.



If you are using [Vim], add the following to your `.vimrc` file:



    if &term =~ "ansi"

      set mouse=a

    endif



However, I was not able to get [Vim] to respect this setting unless I

set `TERM=xterm`, which is not ideal because [mTCP]'s screen-updating

mechanism uses `ansi` sequences rather than `xterm` sequences.



Modify your `.bashrc` to add the following before the part that

references `force_color_prompt`:



    if [ "$TERM" = "ansi" ]; then

        force_color_prompt=yes

    fi



If you would prefer a monochrome prompt, leave out

`force_color_prompt=yes`.



If you want to toggle printing while using [bash] using keystrokes,

you can add the following to your `.bashrc` file:



    bind -x '"\eOP":"echo -n -e \\e[5i"'

    bind -x '"\eOQ":"echo -n -e \\e[4i"'



This tells [bash] that when you press F1, it should send the escape

sequence for turning printing on, and when you press F2, it should send

the escape sequence for turning printing off.



Add a `.mailcap` file to your home directory that contains:



    image/*; show %s



This will signal to other applications that the [show] command should

be used to display images.



If you are using [Lynx], you can set `USE_MOUSE:TRUE` in your

`/etc/lynx.cfg` file to enable mouse support.



You can also view images using [Sixel graphics] while using [Lynx].

You can press `*` to show links to images, or set

`MAKE_LINKS_FOR_ALL_IMAGES:TRUE` in your `/etc/lynx.cfg` file to turn

this feature on by default.  When you click on a link to an image,

your `~/.mailcap` file will be consulted and the [show] command will be

used to show the image.



You can also view images while using [Links].  To set this up, go to

the Setup menu (press Escape to open the menu bar) and go to

Associations.  Then you can add file associations for images.  The

first "Label" should be, e.g., "PNG," and the "Content-Type" should be

`image/png`, and "Program" should be `show %`.  Unselect "Block

terminal while program running" (this causes problems).  Make sure

that "Run on terminal" is selected.  Unselect "Ask before opening."

Don't select "Accepts HTTP URLs" or "Accepts FTP URLs."  Then save the

Association and repeat the process for `image/jpeg` and `image/gif`.

Then do "Save options" under "Setup."  This will create a file

`~/.links2/links.cfg`.  The file will contain something like the

following:



    association "PNG" "image/png" "show %" 11 1

    association "JPEG" "image/jpeg" "show %" 11 1

    association "GIF" "image/gif" "show %" 11 1



Image support is a little better in [Lynx] than it is on [Links]

because it will show a link to an image that is itself a hyperlink.



If you use Midnight Commander, you can edit the file

`/usr/lib/mc/ext.d/image.sh` and change this line:



    ("${MC_XDG_OPEN}" "${MC_EXT_FILENAME}" >/dev/null 2>&1) || \



to:



    ("${MC_XDG_OPEN}" "${MC_EXT_FILENAME}") || \



Then, if your `~/.mailcap` has been set up as discussed above, the

`xdg-open` command will run `show` in the terminal when you open an

image file.



If you use [R], you might want to use this shorthand for showing a

[ggplot2] image:



    sx <- function(){

      ggsave("graph.png", width=3.2, height=2.4)

      system("show graph.png")

    }



## Compiling



I compiled [TELNET.EXE] and [TELNETNU.EXE] using [Open Watcom 1.9]

inside [DosBox] on a Linux machine.



I created a folder `~/dos` and installed Watcom under `~/dos/WATCOM`

and installed the [mTCP] source code under `~/dos/MTCP`.  I used the default

DosBox configuration (see `~/.dosbox`) with this at the end:



    [autoexec]

    # Lines in this section will be run at startup.

    # You can put your MOUNT lines here.

    @echo off

    mount c ~/dos

    SET PATH=C:\WATCOM\BINW

    SET WATCOM=C:\WATCOM

    SET INCLUDE=C:\WATCOM\H;C:\MTCP\TCPINC;C:\MTCP\INCLUDE

    C:\

    CD C:\MTCP\APPS\TELNET



The COMMAND.COM in [DosBox] limits command lines to 128 characters and

there does not appear to be a way to change this.  So I had to modify

the [MAKEFILE] by commenting out this line:



    compile_options += -i=$(tcp_h_dir) -i=$(common_h_dir)



In its place, I used the `INCLUDE` environment variable to let the

compiler know where the `.h` files are.



Then I was able to compile Telnet by running `wmake` from the

`~/dos/MTCP/APPS/TELNET` directory.



I created a batch file called `MAKE.BAT` to recompile only the parts I was editing:



    del telnet.exe

    del telnet.obj

    del telnetsc.obj

    del telnetsx.obj

    del telnet.map

    del misc.obj

    wmake telnet.exe config=UTF.H



This is much faster than waiting for a full `wmake` to complete.



To build a version of `telnet.exe` without the Unicode translation feature

support, use the `NOUTF.H` file instead of `UTF.H`.



For a final build, run `wmake` and then `wmake patch`, and generate

both `TELNETNU.EXE` and `TELNET.EXE`.  (See the file `MAKEALL.BAT`.)



[ansi.src]: https://github.com/jhpyle/mTCP/blob/master/ansi.src

[MAKEFILE]: https://github.com/jhpyle/mTCP/blob/master/MTCP/APPS/TELNET/MAKEFILE

[TELNET.EXE]: https://github.com/jhpyle/mTCP/blob/master/bin/telnet.exe

[TELNETNU.EXE]: https://github.com/jhpyle/mTCP/blob/master/bin/telnetnu.exe

[bin]: https://github.com/jhpyle/mTCP/blob/master/bin

[mTCP]: https://www.brutman.com/

[ansi.el]: https://github.com/jhpyle/mTCP/blob/master/ansi.el

[DECSET]: https://invisible-island.net/xterm/ctlseqs/ctlseqs.pdf

[Code Page 437]: https://en.wikipedia.org/wiki/Code_page_437

[MOUSE.COM]: https://www.computerhope.com/issues/ch000007.htm

[Open Watcom 1.9]: https://sourceforge.net/projects/openwatcom/files/open-watcom-1.9/

[DosBox]: https://www.dosbox.com/

[Vim]: https://www.vim.org/

[Emacs]: https://www.gnu.org/software/emacs/

[Sixel]: https://en.wikipedia.org/wiki/Sixel

[Sixel graphics]: https://en.wikipedia.org/wiki/Sixel

[show]: https://github.com/jhpyle/mTCP/blob/master/sixel/show

[tprint]: https://github.com/jhpyle/mTCP/blob/master/printing/tprint

[stopprint]: https://github.com/jhpyle/mTCP/blob/master/printing/stopprint

[startprint]: https://github.com/jhpyle/mTCP/blob/master/printing/startprint

[install.sh]: https://github.com/jhpyle/mTCP/blob/master/install.sh

[R]: https://www.r-project.org/

[ggplot2]: https://ggplot2.tidyverse.org/

[Links]: https://en.wikipedia.org/wiki/Links_(web_browser)

[Lynx]: https://en.wikipedia.org/wiki/Lynx_(web_browser)

[unicode.org]: https://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/PC/

[`config`]: https://github.com/jhpyle/mTCP/blob/master/config

[Code Page]: https://en.wikipedia.org/wiki/Code_page

[Code Page 437]: https://en.wikipedia.org/wiki/Code_page_437

[Code Page 737]: https://en.wikipedia.org/wiki/Code_page_737

[Code Page 775]: https://en.wikipedia.org/wiki/Code_page_775

[Code Page 850]: https://en.wikipedia.org/wiki/Code_page_850

[Code Page 852]: https://en.wikipedia.org/wiki/Code_page_852

[Code Page 855]: https://en.wikipedia.org/wiki/Code_page_855

[Code Page 857]: https://en.wikipedia.org/wiki/Code_page_857

[Code Page 860]: https://en.wikipedia.org/wiki/Code_page_860

[Code Page 861]: https://en.wikipedia.org/wiki/Code_page_861

[Code Page 862]: https://en.wikipedia.org/wiki/Code_page_862

[Code Page 863]: https://en.wikipedia.org/wiki/Code_page_863

[Code Page 864]: https://en.wikipedia.org/wiki/Code_page_864

[Code Page 865]: https://en.wikipedia.org/wiki/Code_page_865

[Code Page 866]: https://en.wikipedia.org/wiki/Code_page_866

[Code Page 869]: https://en.wikipedia.org/wiki/Code_page_869

[Code Page 874]: https://en.wikipedia.org/wiki/Code_page_874

[Hercules Graphics Card]: https://en.wikipedia.org/wiki/Hercules_Graphics_Card

[VGA]: https://en.wikipedia.org/wiki/Video_Graphics_Array

[MCGA]: https://en.wikipedia.org/wiki/Multi-Color_Graphics_Array

[`img2sixel`]: https://github.com/saitoha/libsixel

[CGA]: https://en.wikipedia.org/wiki/Color_Graphics_Adapter

[Enhanced Keyboard]: https://en.wikipedia.org/wiki/IBM_PC_keyboard

[IBM PC 5150]: https://en.wikipedia.org/wiki/IBM_Personal_Computer

[IBM PC model 5150]: https://en.wikipedia.org/wiki/IBM_Personal_Computer

[IBM PC/XT]: https://en.wikipedia.org/wiki/IBM_Personal_Computer_XT

[IBM PC/AT]: https://en.wikipedia.org/wiki/IBM_Personal_Computer/AT

[IBM XT 286]: https://en.wikipedia.org/wiki/IBM_Personal_Computer_XT#IBM_XT_286

[PS/2]: https://en.wikipedia.org/wiki/IBM_PS/2

[IBM PS/2 Model 25]: https://en.wikipedia.org/wiki/IBM_PS/2

[EGA]: https://en.wikipedia.org/wiki/Enhanced_Graphics_Adapter

[ssh]: https://en.wikipedia.org/wiki/Secure_Shell

[bash]: https://en.wikipedia.org/wiki/Bash_(Unix_shell)

[Diablo 630]: https://en.wikipedia.org/wiki/Diablo_630

[mTCP-src_2022-07-01.zip]: http://www.brutman.com/mTCP/download/mTCP-src_2022-07-01.zip

[first terminals]: https://en.wikipedia.org/wiki/Teletype_Model_33

[VT52]: https://en.wikipedia.org/wiki/VT52

[VT100]: https://en.wikipedia.org/wiki/VT100

[Midnight Commander]: https://midnight-commander.org/