LVTL-X: a compact and fair VTL-2 port to POSIX AWK

About

LVTL-X is a port of the VTL-2 retro programming language interpreter to the POSIX AWK runtime. Unlike the previous effort, LVTL-W, that only worked in BusyBox and GAWK, this version works in any POSIX-compliant environment. On top of that, LVTL-X is extremely compact and takes under 100 SLOC of portable and readable AWK code.

Usage

The easiest way is to run the ./lvtl shell wrapper, either stand-alone or with a program file path to preload. You can also specify a non-default AWK interpreter to use with the AWK environment variable for the wrapper to use.

Alternatively, you can run the LVTL-X script directly like this:

POSIXLY_CORRECT=1 awk -f lvtl-x.awk -- [/path/to/your/vtl/program.vtl] -

If running without a wrapper and specifying a program to preload, don't forget to put another - after it.

Differences from the Altair original

LVTL-X stands out from other LVTL versions by being closer to the original VTL-2, but still has some important differences that shouldn't be ignored:

both LF and CRLF are accepted (but not saved into RAM)
only LFs are printed instead of CRLFs
maximum line length is not enforced
all whitespace after the line number is fully ignored
any whitespace within expressions is also insignificant
parentheses are NOT auto-closed at the end of the statement
only 26 characters (A-Z) are valid generic variable names
supports all standard VTL-2 binary operators: +, -, *, /, =, >, <
jumps to itself (like 10 #=10) are prohibited and counted as nops
no file I/O (only the option to preload VTL code from a file)
self-modifying programs won't work correctly

Nevertheless, any program that's valid on LVTL-X will run on the original VTL-2/02 implementations too.

Credits

Created by Luxferre in 2026, released into the public domain with no warranties.