modbus-cli

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 |_|  |_|\___/|___/|___/ \___/|___/      \___|____|___|

Like curl, but for Modbus.

A dead-simple command-line tool for reading and writing Modbus TCP and RTU registers. Beautiful terminal UI. No GUI, no config files, no bloat.

pip install modbus-curl

Features

• Styled output -- color-coded panels, value bars, gradient theme
• Live dashboard -- full-screen TUI with sparkline history, change detection, and keybindings (powered by Textual)
• Smart addressing -- auto-detects register type from standard Modbus notation (40001 = holding, 30001 = input, etc.)
• TCP + Serial RTU -- works with network devices and serial RS485 buses
• Multiple formats -- decimal, hex, binary, signed 16-bit
• Progress bars -- animated scan and dump with real-time feedback
• CSV export -- dump register maps straight to file
• JSON output -- pipe read/scan/dump output into jq and automation tools

Quick Start

# Read 5 holding registers
modbus read 192.168.1.10 40001 --count 5

# Write a value
modbus write 192.168.1.10 40001 1234

# Scan for devices on the bus
modbus scan 192.168.1.10 --range 1-10

# Open live monitoring dashboard
modbus watch 192.168.1.10 40001 --count 8

# Dump 200 registers to CSV
modbus dump 192.168.1.10 40001 40200 --csv registers.csv

Why?

Every Modbus device ships with register maps. To test them, you currently need:

• A Windows GUI tool (QModMaster, ModRSsim, Simply Modbus)
• Or a throwaway Python script with pymodbus boilerplate

Neither works well when you're SSH'd into a headless gateway, debugging a PLC at 2am, or just want a quick sanity check.

modbus-cli gives you one command. That's it.

Install

pip install modbus-curl

Requires Python 3.8+. No binary dependencies. Works on Linux, macOS, and Windows.

Docker

# Build local image
docker build -t 19bk/modbus-cli .

# Run a command inside the container
docker run --rm 19bk/modbus-cli read 192.168.1.10 40001 -c 10

Commands

modbus read -- Read registers

# Read a single holding register
modbus read 192.168.1.10 40001

# Read 10 holding registers with value bars
modbus read 192.168.1.10 40001 --count 10

# Read input registers in hex
modbus read 192.168.1.10 30001 --count 4 --format hex

# Read coils
modbus read 192.168.1.10 1 --count 8 --type coil

# Read via serial RTU
modbus read --serial /dev/ttyUSB0 40001 --slave 2 --baudrate 19200

# Signed 16-bit values
modbus read 192.168.1.10 40001 -c 5 -f signed

# JSON output for scripting
modbus read 192.168.1.10 40001 -c 5 --json | jq '.registers[].value'

Output includes styled panels, connection status, and visual value bars showing register magnitude at a glance.

Address notation: Uses standard Modbus addressing. 40001-49999 = holding registers, 30001-39999 = input registers, 10001-19999 = discrete inputs, 1-9999 = coils. Or pass raw 0-based addresses with --type.

modbus write -- Write registers

# Write a single holding register
modbus write 192.168.1.10 40001 1234

# Write multiple registers
modbus write 192.168.1.10 40001 100 200 300

# Write a coil ON
modbus write 192.168.1.10 1 1 --type coil

modbus scan -- Find active devices

# Scan all slave IDs (1-247) with animated progress bar
modbus scan 192.168.1.10

# Scan a specific range
modbus scan 192.168.1.10 --range 1-10

# Scan serial bus
modbus scan --serial /dev/ttyUSB0 --range 1-50

# JSON output
modbus scan 192.168.1.10 --range 1-10 --json

Devices are reported as they're found, with a progress bar showing scan completion.

modbus watch -- Live monitoring dashboard

# Watch 4 registers with full-screen TUI
modbus watch 192.168.1.10 40001 --count 4

# Watch at 500ms intervals in hex
modbus watch 192.168.1.10 40001 -c 8 -i 0.5 -f hex

Opens a full-screen Textual dashboard with:

• Live data table with zebra-striped rows
• Sparkline history per register (up to 60 samples)
• Change detection showing deltas between polls
• Stats bar with poll count, change count, and polling rate

Keybindings:

Key	Action
q	Quit
r	Reset stats and history
f	Cycle format (decimal / hex / bin / signed)
p	Pause / resume polling

modbus dump -- Export register ranges

# Dump 100 registers to terminal with progress bar
modbus dump 192.168.1.10 40001 40100

# Export to CSV
modbus dump 192.168.1.10 40001 40200 --csv registers.csv

# Dump in hex format
modbus dump 192.168.1.10 40001 40200 -f hex

# Dump as JSON
modbus dump 192.168.1.10 40001 40020 --json

Reads in chunks of 125 registers (Modbus protocol max). Shows an animated progress bar for large ranges.

Options

Flag	Short	Description
--port	-p	TCP port (default: 502)
--serial	-s	Serial port (e.g. /dev/ttyUSB0), overrides TCP
--baudrate	-b	Serial baud rate (default: 9600)
--slave	-u	Slave/unit ID (default: 1)
--count	-c	Number of registers to read (default: 1)
--type	-t	Register type: holding, input, coil, discrete
--format	-f	Output format: decimal, hex, bin, signed
--timeout		Connection timeout in seconds (default: 3)

Common Workflows

Quick register check on a field device:

modbus read 10.0.0.50 40001 -c 20 -f hex

Find all devices on a serial bus:

modbus scan --serial /dev/ttyUSB0 --range 1-50 --timeout 0.3

Monitor a sensor value live:

modbus watch 192.168.1.10 40010 -i 0.5

Dump a full register map for documentation:

modbus dump 192.168.1.10 40001 40500 --csv device_map.csv

Compare before/after a config change:

modbus dump 192.168.1.10 40001 40050 --csv before.csv
# ... make changes ...
modbus dump 192.168.1.10 40001 40050 --csv after.csv
diff before.csv after.csv

Built With

• pymodbus -- Modbus protocol implementation
• Click -- CLI framework
• Rich -- Terminal formatting and styled output
• Textual -- TUI framework for the watch dashboard

Development

git clone https://github.com/19bk/modbus-cli.git
cd modbus-cli
python -m venv .venv
source .venv/bin/activate
pip install -e .
modbus --help

Contributing

Issues and PRs welcome. If you work with Modbus devices and want a feature, open an issue describing your use case.

License

MIT