Variables¶

Termapy has a variable system that lets you define, expand, and reuse values across commands, scripts, and config fields. Variables use $(NAME) syntax.

Setting variables¶

Assign variables directly at the command line (no / prefix needed):

$(ADDR) = 01
$(PORT) = COM7
$(LABEL) = sensor_a

Or use the REPL command:

/var.set ADDR 01

Capturing command output¶

Use <- to run a command and store its result in a variable. The right-hand side is executed - as a REPL command (if it starts with /) or as a device command (sent to the serial port) - and the response is captured.

$(BAUD) <- /port.baud_rate    # captures REPL command output
$(TEMP) <- AT+TEMP            # captures device response

Using variables¶

Variables expand anywhere: serial commands, REPL commands, scripts:

AT+ADDR=$(ADDR)
/print Reading from $(ADDR)
/cap.text $(LABEL)_log.txt timeout=5s

Built-in variables¶

Dynamic variables update each time they are expanded. Launch variables are frozen when the app starts. Session variables are set once when a script launches from the Scripts button or Run menu.

Custom time formats¶

Any datetime variable accepts a strftime format after a colon. The format runs to the closing paren and may contain its own colons:

$(DATETIME:%Y%m%d_%H%M%S)   # 20260707_143000 -- filename-safe (no colons)
$(TIME:%H%M)                # 1430
$(SESSION_DATE:%d-%b)       # 07-Jul -- works on frozen vars too

This is the way to get a colon-free timestamp for filenames, since the default $(DATETIME) (2026-07-07 14:30:00) contains colons and spaces.

Environment variables¶

Access OS environment variables with $(env.NAME) syntax. This is especially useful in config files for values that differ per machine:

"port": "$(env.TERMAPY_PORT|COM4)"

The | inside the $(env.NAME|...) provides a fallback when the env variable is unset.

Env expansion composes with port-resolution fallback¶

For the port field specifically there is a second, independent | that lives at the port-resolution layer: termapy splits the port value on | at open time and tries each candidate (device name or USB serial number) in order. These layers compose cleanly -- env expansion runs first, then port resolution:

"port": "$(env.DEVICE_SN)|COM3"

• $(env.DEVICE_SN) expands to the env value (or stays as the placeholder if unset).
• The resulting string is fed to port resolution, which tries the SN first and COM3 if it doesn't match.

Both forms are valid and do slightly different things:

• "port": "$(env.DEVICE_SN|COM4)" -- env-layer fallback. If DEVICE_SN is unset, the value is literally COM4.
• "port": "$(env.DEVICE_SN)|COM3" -- port-resolution fallback. The env value (whatever it is, even a wrong SN) is tried first, then COM3 if resolution fails. The idiomatic form for port specs.

Env vars never reach the wire automatically¶

$(env.NAME) expands in config values (like port above) and in REPL commands (/print $(env.HOME), /var set x $(env.TOKEN)), but not in bare device commands -- typing AT+X=$(env.SECRET) sends the literal text, never the value, so environment secrets stay off the serial wire.

The on_connect_cmd family (on_connect_cmd, tui_/cli_/mcp_on_connect_cmd) follows exactly this rule: each line is dispatched as if you had typed it, so /-commands in it expand $(env.X) while device commands do not. They are deliberately not pre-expanded at config-load time -- if you need an env value in a connect-time device command, put it in a user variable via a /-command first ($(NAME) user variables do expand on the wire).

See ports.md for the full port-spec grammar, and Using with Git for team workflow details.

Template placeholders¶

Curly-brace {} placeholders are per-script-run stamps: the auto-incrementing sequence counters plus this run's start time and elapsed time. They are the counterpart to $(NAME) variables, which substitute ambient values (config, environment, wall-clock). The rule:

• {} = per-run: counters ({seqN}), run start ({starttime}), elapsed ({elapsed}). Refreshed at each outermost script boundary.
• $() = ambient: everything else, including the wall clock. For a current-time stamp use $(DATETIME:...), not a {} placeholder.

/ss.svg capture_{seq1+}          # capture_1.svg, capture_2.svg, ...
AT+READ {seq2+}                  # independent counter
/print done in {elapsed}

seq1 is the top level; incrementing counter N resets all deeper (higher-numbered) counters to 0, so bumping an outer level restarts the inner ones. {starttime} and {elapsed} measure from script start inside a run, or from app start when typed interactively.

The former {datetime} and {clock} placeholders were retired: they were ambient wall-clock stamps, so they moved to $() as $(DATETIME:%Y%m%d_%H%M%S) and $(TIME). Old scripts and configs are rewritten automatically.

Variable commands¶

Escaping¶

Use \$ to prevent expansion:

/print \$(ADDR) = $(ADDR)     # prints: $(ADDR) = 01

Use /raw to send a line with no expansion at all:

/raw $(GPS),NMEA,0            # sends literal $(GPS),NMEA,0

Scope¶

User variables persist for the session. They are cleared automatically when a script launches from the Scripts button or Run menu, but NOT when /run is typed interactively. Use /var.clear to reset manually.