TAB4DOS

A small resident utility (TSR) for MS-DOS that adds bash-style TAB completion, command history, and command-line editing to the standard COMMAND.COM prompt.

It hooks INT 21h / AH=0Ah (buffered line input) and replaces COMMAND.COM's line editor with its own, while leaving everything else untouched.

Download: https://github.com/Projanglez/TAB4DOS/releases/latest

Features

• TAB / Shift+TAB — complete and cycle matches (forward / backward) for files, directories, path fragments, DOS internal commands, and executables found on PATH.
• Up / Down — browse command history (64 entries), replaces DOSKEY
• Line editing — Left/Right, Home/End, Del, Ins (insert/overwrite), Ctrl+Left/Ctrl+Right (jump word), ESC (clear line).
• Small footprint — ~9 KB resident. The command list and the history ring are kept in small files (TAB4DOS.IDX / TAB4DOS.HST) next to the EXE (or in %TEMP% with /usetemp), not in resident memory; with SmartDrive these reads/writes are effectively RAM-speed.
• See full changelog for more details

Requirements

• CPU: Intel 8086/8088 or later. The binary is pure 16-bit real-mode code with no 386- or 286-specific instructions.
• OS: MS-DOS 3.0 or later. It uses DOS 2.0+ services (file handles, FindFirst/Next, environment, get/set interrupt vector, TSR) plus the program path in the environment block (DOS 3.0+) to find its own directory. Developed and tested on MS-DOS 6.22.
• Files location: by default TAB4DOS.IDX / TAB4DOS.HST are written next to tab4dos.exe. With /usetemp they go to %TEMP% (or %TMP%); if neither variable is set, TAB4DOS prints an error and does not install.
• Optional: SmartDrive (SMARTDRV) makes the per-keystroke index/history file access RAM-fast.

Usage

TAB4DOS          Install the TSR (shows a banner)
TAB4DOS /s       Install silently (no output)
TAB4DOS /u       Uninstall and free the resident memory
TAB4DOS /h       Show help
TAB4DOS /usetemp Store index/history in %TEMP% (default: program directory)

After installing, just type at the DOS prompt and use the keys above.

Prior art

Adding history and filename completion to the bare COMMAND.COM prompt is an old idea, kudos for all persons who developed a similar program.

TAB4DOS aims for a single, tiny (~9 KB) TSR that combines bash-style TAB completion, history, and full line editing, while keeping COMMAND.COM itself in place — and keeps its data out of resident memory by offloading the command index and history ring to small files.

Build

Built with Open Watcom 16-bit (real mode) — not wcl386; a TSR runs in real mode.

1. Install Open Watcom (the build expects it under C:\WATCOM).

2. From a CMD prompt, run:

   build.bat
   

   Output: tab4dos.exe. The script compiles with wcc -bt=dos -ms -os -s -zq (-s is mandatory — it disables Watcom's __STK stack checks, which would falsely fire on the foreign stack a TSR runs on) and links with wlink @tab4dos.lnk.

Notes

• Test on real DOS hardware (or a faithful emulator). DOSBox ships its own built-in TAB completion that overrides this tool, so results there are not meaningful.
• This software was developed with the help of an AI coding assistant (Claude Code).

Contributing

Bug reports and ideas are welcome — please open an issue. Since this is a real-mode DOS TSR, see CHANGELOG.md for the version history and the build notes above before sending a pull request.

License

MIT — see LICENSE.

TAB4DOS is free and donationware: If you like it, you can leave a tip at liberapay.com/Projanglez. Entirely optional — the tool is and stays fully functional without it.

Copyright (c) 2026 Projanglez