CLI

Commands

nexus run [FILE|-]

Interpret a Nexus source file:

nexus run program.nx
nexus run --allow-console --allow-fs program.nx
echo 'let main = fn () -> unit do return () end' | nexus run -

Supports stdin piping and shebang scripts.

nexus build [FILE|-]

Compile to a WASM component:

nexus build program.nx                  # outputs main.wasm
nexus build program.nx -o output.wasm   # custom output path

Requires wasm-merge for dependency bundling. Configure via:

• --wasm-merge PATH flag
• NEXUS_WASM_MERGE environment variable

Resolution order: --wasm-merge > NEXUS_WASM_MERGE > wasm-merge from PATH.

Inspect declared capabilities:

nexus build program.nx --explain-capabilities       # human-readable
nexus build program.nx --explain-capabilities=json   # machine-readable

Run the built component:

wasmtime run -Scli main.wasm
wasmtime run -Scli -Shttp -Sinherit-network -Sallow-ip-name-lookup -Stcp main.wasm

nexus check [FILE|-]

Parse and typecheck only. No execution, no WASM output.

nexus check program.nx

REPL

Run nexus with no arguments to start an interactive session:

nexus

• Persistent definitions across inputs
• Multi-line input support (prompt changes to ..)
• PermConsole auto-enabled
• :help for commands, :exit or Ctrl-D to quit

Capability Flags

Flag	Permission	Description
--allow-fs	PermFs	Filesystem access
--allow-net	PermNet	Network access
--allow-console	PermConsole	Standard I/O
--allow-random	PermRandom	Random number generation
--allow-clock	PermClock	Clock and timers
--allow-proc	PermProc	Process control
--preopen DIR	(with PermFs)	Preopen a directory for filesystem access

Capability flags apply to nexus run. The compiled WASM binary encodes required capabilities in the nexus:capabilities section – the host runtime (e.g., wasmtime) enforces them at execution time. See WASM and WASI.

Development

Build and run from source:

cargo run -- run program.nx --allow-console
cargo run -- build program.nx
cargo run -- check program.nx