# SQR / SQRM / SQRL (SQRELF) Formats

ModuOS userland programs and related binaries use the **SQRELF** naming convention.

## Terminology

- **SQR** == **SQRELF** == **Squirrel Executable and Linkable Format**
  - Typical file extension: `.sqr`
  - Meaning: a normal executable program (similar role to an ELF executable on Linux).

- **SQRM** == **SQRELFM** == **Squirrel Executable and Linkable Format Module**
  - Typical file extension: `.sqrm`
  - Meaning: a loadable module (kernel module / driver module).

- **SQRL** == **SQRELFL** == **Squirrel Executable and Linkable Format Library**
  - Typical file extension: `.sqrl`
  - Meaning: a shared/static library style binary meant to be linked against.

## Relationship to ELF

At a binary level, ModuOS currently builds userland programs with an **ELF64 toolchain** (`x86_64-elf-gcc` + `x86_64-elf-ld`).

The **SQR/SQRM/SQRL** names are therefore:

- A *project naming convention* for what the binary represents (executable/module/library)
- A *file extension convention* used by the ModuOS ecosystem

In other words:

- `.sqr` files are effectively **ELF64 executables** used by ModuOS.

## Where these files live

- ISO image apps: `targets/AMD64/iso/Apps/*.sqr`
- Example apps shipped on the ISO: `cat.sqr`, `echo.sqr`, `memtest.sqr`, `sh.sqr`, `neofetch.sqr`

## Building a `.sqr`

```bash
cd userland
x86_64-elf-gcc -c program.c -o program.o
x86_64-elf-ld -T user.ld program.o -o program.sqr
```