CLI · fx docs

Everyday commands

Command	Purpose
`fx doctor`	Check C toolchain + zspec paths
`fx version`	Print version (expect `v0.7.1`)
`fx help`	Show help
`fx new <name>`	Create a project from a scaffold
`fx check <file.fx>`	Parse and typecheck
`fx run <file.fx>`	Emit C, link, run
`fx build <file.fx>`	Emit C and link (do not run)
`fx emit-c <file.fx> -o <dir>`	Emit `.c` / `.h` only

fx doctor

Reports whether gcc, clang, and/or zig are on your PATH, and whether zspec headers/libraries can be found by walking up from the current directory. Exit code 0 if at least one C toolchain is found.

fx new

fx new hello
fx new tiny --scaffold minimal
fx new firmware --scaffold embedded

Scaffold	Intent
`simple` (default)	Named region + `import std/vec`; stages `std/`
`minimal`	Bare `main` returning 42
`embedded`	Tiny arena footprint; builtin `vec_*`; no staged `std/`

fx run / fx build

fx run main.fx
fx run main.fx --release
fx build main.fx -o out

Flag	Meaning
`-o <dir>`	Output directory (default `out/`)
`--release`	Optimize more; less debug instrumentation
`--watch`	Rebuild when sources change
`--no-zspec`	Do not link zspec (only when appropriate)
`--host <file.c>`	Use this C file as `main`; link fx objects with it
`--link-args-file`	Extra linker args, one per line
`--link-include` / `--link-dir` / `--link-lib`	Extra include/lib paths

Default linking expects gcc and the zspec library that matches your OS (build/gcc or build/gcc-linux).

fx emit-c

fx emit-c main.fx -o out_c

Agent / editor helpers

Command	Role
`fx lsp`	Language server (stdio)
`fx mcp`	Lean MCP server (`fx_check`, `fx_locate`, `fx_run`, …)
`fx locate --c-file <f.c> --line <n>`	Map a C line back to fx via `.fxmap`

Exit codes

Application main return values become process exit codes when you fx run (the simple scaffold returns 42). Tooling failures use non-zero codes. fx doctor exits 1 when no C toolchain is found.