feat: add --json flag to read, dump, and scan commands by zakiscoding · Pull Request #5 · 19bk/modbus-cli

zakiscoding · 2026-03-12T16:39:53Z

Summary

Adds a --json flag to the read, dump, and scan commands
When --json is passed, outputs structured JSON instead of Rich tables
Enables piping into jq or other tools

Usage

modbus read 192.168.1.10 40001 -c 5 --json | jq '.registers[].value'
modbus dump 192.168.1.10 40001 40100 --json > dump.json
modbus scan 192.168.1.10 --json | jq '.devices'

JSON Schema (read)

{
  "host": "192.168.1.10",
  "type": "holding",
  "slave": 1,
  "registers": [
    {"address": 40001, "raw": 237, "value": "237"}
  ]
}

Closes #1

Closes #1 Outputs results as JSON instead of Rich tables when --json is passed, enabling piping into jq or other tools: modbus read 192.168.1.10 40001 -c 5 --json | jq '.registers[].value'

Copilot

Pull request overview

This PR adds a --json flag to the read, dump, and scan commands of modbus-cli, enabling structured JSON output for piping into tools like jq. It also adds --float, --byte-order, and --word-order options to the read command for decoding register pairs as 32-bit IEEE 754 floats (not mentioned in the PR description).

Changes:

Added --json flag to read, dump, and scan commands that outputs structured JSON instead of Rich tables
Added --float decoding support with --byte-order and --word-order options to the read command
Added _decode_floats helper function for IEEE 754 float decoding from register pairs

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

Copilot · 2026-03-12T16:43:57Z

+    if as_json:
+        print(__import__("json").dumps({"host": host, "range": scan_range, "register": register, "devices": [{"slave_id": sid, "register_value": val} for sid, val in found]}, indent=2))
+        return


When --json is used, Rich progress bars, spinner output, and "Found slave" messages are still printed to the console (lines 355-392) before the JSON is emitted. This pollutes stdout/stderr and makes the output unsuitable for piping into jq or other tools, which is the stated purpose of the --json flag. The JSON check should be moved earlier, or Rich output should be suppressed (e.g., by redirecting the console to stderr or skipping the progress display) when as_json is true.

Copilot · 2026-03-12T16:43:58Z

+    if as_json:
+        registers = [{"address": start_address + i, "raw": val, "value": _format_value(val, fmt)} for i, val in enumerate(all_values)]
+        print(__import__("json").dumps({"host": host, "type": detected_start, "slave": slave, "registers": registers}, indent=2))
+        return


Similar to the scan command issue: when --json is used, Rich output (connection header at line 539, progress bars at lines 544-557) is still printed to the console before the JSON is emitted. This contaminates the JSON output and breaks piping. The Rich output should be suppressed or redirected to stderr when as_json is true.

Copilot · 2026-03-12T16:43:58Z

+        from rich.table import Table
+        from rich.panel import Panel


Table and Panel are already imported at the top of the file (lines 9-10). These local re-imports are unnecessary.

Suggested change

from rich.table import Table

from rich.panel import Panel

Copilot · 2026-03-12T16:43:58Z

+            pairs = [{"address": address + i * 2, "value": floats[i]} for i in range(len(floats))]
+            print(__import__("json").dumps({"host": host, "type": detected_type, "slave": slave, "float_values": pairs}, indent=2))


IEEE 754 special values (NaN, Infinity) can appear in Modbus register data. Python's json.dumps will serialize these as bare NaN/Infinity tokens, which are not valid JSON and will cause downstream JSON parsers (like jq) to fail. Consider using json.dumps(..., allow_nan=False) with error handling, or converting these values to null or string representations before serialization.

Copilot · 2026-03-12T16:43:59Z

+        floats = _decode_floats(list(values), byte_order=byte_order, word_order=word_order)
+        if as_json:
+            pairs = [{"address": address + i * 2, "value": floats[i]} for i in range(len(floats))]
+            print(__import__("json").dumps({"host": host, "type": detected_type, "slave": slave, "float_values": pairs}, indent=2))


json is already imported at the top of the file (line 3). Using __import__("json") here is unnecessary and inconsistent. Just use json.dumps(...) directly.

Copilot · 2026-03-12T16:43:59Z

+            addr_display = address + i if not reg_type else raw_address + i
+            int_val = int(val)
+            registers.append({"address": addr_display, "raw": int_val, "value": _format_value(int_val, fmt) if not isinstance(val, bool) else str(int_val)})
+        print(__import__("json").dumps({"host": host, "type": detected_type, "slave": slave, "registers": registers}, indent=2))


Same issue: json is already imported at the top of the file. Use json.dumps(...) instead of __import__("json").dumps(...). This pattern is repeated in all three commands (read, scan, dump).

Copilot · 2026-03-12T16:43:59Z


+    if as_float:
+        if len(values) % 2 != 0:
+            from .theme import error_panel


error_panel is already imported at the top of the file (line 14). This local re-import is unnecessary.

Suggested change

from .theme import error_panel

Copilot · 2026-03-12T16:43:59Z

+@click.option("--float", "as_float", is_flag=True, default=False, help="Decode register pairs as 32-bit IEEE 754 floats.")
+@click.option("--byte-order", default="BE", type=click.Choice(["BE", "LE"]), help="Byte order for float decoding (default: BE).")
+@click.option("--word-order", default="BE", type=click.Choice(["BE", "LE"]), help="Word order for float decoding (default: BE).")


The --float, --byte-order, and --word-order options are not mentioned in the PR description or issue #1. These are unrelated features bundled into a PR that's supposed to only add --json support. Consider splitting these into a separate PR for cleaner review and history.

Copilot · 2026-03-12T16:44:00Z

+    if as_json:
+        registers = []
+        for i, val in enumerate(values):
+            addr_display = address + i if not reg_type else raw_address + i
+            int_val = int(val)
+            registers.append({"address": addr_display, "raw": int_val, "value": _format_value(int_val, fmt) if not isinstance(val, bool) else str(int_val)})
+        print(__import__("json").dumps({"host": host, "type": detected_type, "slave": slave, "registers": registers}, indent=2))
+        return


When --json is used with the read command, Rich output is still written to stdout before the JSON (e.g., console.print() at line 171, connection_header() at line 176, console.status() at lines 173 and 178). This contaminates the JSON output when piping. Consider suppressing Rich output or redirecting it to stderr when as_json is true.

19bk · 2026-03-12T16:49:59Z

Closing in favor of the focused PRs: #8 (JSON, merged) and #6 (float, pending rebase). Splitting features into separate PRs makes review easier. Appreciate the work!

feat: add --json flag to read, dump, and scan commands

454c4c7

Closes #1 Outputs results as JSON instead of Rich tables when --json is passed, enabling piping into jq or other tools: modbus read 192.168.1.10 40001 -c 5 --json | jq '.registers[].value'

Copilot AI review requested due to automatic review settings March 12, 2026 16:39

Copilot started reviewing on behalf of zakiscoding March 12, 2026 16:40 View session

Copilot AI reviewed Mar 12, 2026

View reviewed changes

19bk closed this Mar 12, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

feat: add --json flag to read, dump, and scan commands#5

feat: add --json flag to read, dump, and scan commands#5
zakiscoding wants to merge 1 commit into
19bk:mainfrom
zakiscoding:feat/json-output-flag

zakiscoding commented Mar 12, 2026

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

Copilot AI Mar 12, 2026

Uh oh!

19bk commented Mar 12, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

		pairs = [{"address": address + i * 2, "value": floats[i]} for i in range(len(floats))]
		print(__import__("json").dumps({"host": host, "type": detected_type, "slave": slave, "float_values": pairs}, indent=2))

Conversation

zakiscoding commented Mar 12, 2026

Summary

Usage

JSON Schema (read)

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

19bk commented Mar 12, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants