The interactive REPL

opp_repl is an IPython shell with every opp_repl public function imported into the top-level namespace, plus convenience variables for every loaded project and a handful of REPL-specific ergonomics.

Upstream references:

• https://github.com/omnetpp/opp_repl/blob/main/doc/repl.md
• https://github.com/omnetpp/opp_repl/blob/main/doc/getting_started.md

Launching

opp_repl --load ~/workspace/omnetpp/omnetpp.opp \ --load ~/workspace/inet/inet.opp

Glob patterns are allowed and --load can be repeated:

opp_repl --load "~/workspace/omnetpp/samples//.opp"

CLI flags

Pre-loaded namespace

On startup every public symbol from opp_repl is imported at the top level — call them without a prefix:

run_simulations(sim_time_limit="1s") run_smoke_tests() build_project() compare_simulations(simulation_project_1=a, simulation_project_2=b)

Press TAB after any partial name to auto-complete function names, method names, and keyword arguments.

Convenience variables

Every loaded project is injected as {name}_project, with hyphens and dots turned into underscores:

• inet.opp --> inet_project
• simu5g.opp --> simu5g_project
• omnetpp-6.3.0.opp --> omnetpp_6_3_0_project

List them: get_simulation_project_variable_names().

Defaults

If the current working directory is inside a loaded project's tree, that project is auto-set as default. Otherwise set explicitly:

set_default_simulation_project(aloha_project)

Or on the command line: -p aloha.

Autoreload

IPython's %autoreload 2 is enabled at startup. Editing Python source files (your own helpers or opp_repl itself) picks up changes before the next command — no restart required.

User module auto-import

At startup the REPL tries import <unix-login-name>, e.g. import alice if $USER is alice. If the module exists, every public name is injected into the namespace. This is the blessed mechanism for per-user helpers, project defaults, and shortcuts — no need to fork opp_repl.

Stopping execution cleanly

Inside a multi-line REPL script, call stop_execution() (or stop_execution(value)) to abort the current cell without a full traceback. Useful for early exits from sourced scripts.

Scripting non-interactively

opp_repl accepts stdin and runs each line as in an interactive session. Pipe a heredoc for one-shot scripted runs:

opp_repl --mcp-port 0 --load aloha.opp <<'EOF' r = run_simulations(config_filter="PureAloha1", sim_time_limit="0.3s") print(r) exit EOF

For CI where IPython-specific features are not needed, prefer the shell wrappers — see opp-repl-cli-tools.

Pitfalls

• --mcp-port defaults to 0 (the MCP server is OFF). Pass a port

(e.g. 9966) to enable TCP mode — which then needs --mcp-token-hash outside opp_sandbox — or use --mcp-socket for the tokenless local transport. Leave both unset in CI / parallel test runs. See opp-repl-mcp-server.

• The user-module auto-import is silent when the module is missing.

If your helpers don't load, check your OS login name vs. module name.

• Running opp_repl without --load and not inside a project tree

gives you a bare REPL — the {name}_project variables only appear after load_opp_file().

See also

• opp-repl-installation — prerequisites.
• opp-repl-concepts — the object model.
• opp-repl-running-simulations — run_simulations() in detail.
• opp-repl-cli-tools — non-interactive shell equivalents.
• opp-repl-mcp-server — expose the REPL to AI agents.
• opp-repl-shared-terminal — let a human and an AI share this REPL.