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dddparser writes JSON to stdout by default. Diagnostic messages, warnings, and errors are sent to stderr so they do not contaminate the JSON stream. You can redirect output to a file with the -output flag, or pipe it directly to other tools. The JSON structure closely mirrors the EU tachograph data specification. Each data block defined in the regulation corresponds to a key in the output object.

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Top-level keys for VU data

When parsing vehicle unit data with -vu, the output object may contain the following top-level keys depending on which data blocks are present in the file:
KeyDescription
vu_overview_1First-generation VU overview — contains member state and VU certificates, control activity, and other overview fields
vu_overview_2Second-generation VU overview
vu_overview_2_v2Second-generation v2 VU overview
vu_activities_1Array of first-generation activity records
vu_activities_2Array of second-generation activity records
vu_activities_2_v2Array of second-generation v2 activity records
vu_events_and_faults_1First-generation events and faults
vu_events_and_faults_2 / vu_events_and_faults_2_v2Second-generation events and faults
vu_detailed_speed_1 / vu_detailed_speed_2Detailed speed data
vu_technical_data_1 / vu_technical_data_2 / vu_technical_data_2_v2Technical data blocks
The verified field on each signed block indicates whether its cryptographic signature was successfully verified against the loaded ERCA certificates.

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Example output structure

A trimmed example of VU JSON output: 
{
  "vu_download_interface_version": "...",
  "vu_overview_1": {
    "verified": true,
    "member_state_certificate": { ... },
    "vu_certificate": { ... },
    "vu_identification": { ... },
    "vu_sensor_paired_records": [ ... ],
    "vu_control_activity_data": { ... }
  },
  "vu_activities_1": [
    {
      "verified": true,
      "vu_driver_activity_daily_records": [ ... ]
    }
  ]
}
All struct fields use the omitempty JSON tag. Any field that is absent from the tachograph file or has a zero value will be omitted entirely from the output. The presence of a key in the output means the corresponding data block was found in the file.

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Pretty-printing output

By default, dddparser outputs compact JSON. Use the -format flag to enable indented output: 
./dddparser -vu -input tachodata.ddd -format
Alternatively, pipe through jq: 
cat tachodata.ddd | ./dddparser -vu | jq .

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Filtering with jq

jq is the most practical way to extract specific fields from Tachoparser output. Install it via your system package manager (apt install jq, brew install jq, etc.).
# Check if first-generation overview signature is verified
cat tachodata.ddd | ./dddparser -vu | jq '.vu_overview_1.verified'

# List all activity record dates from first-generation data
cat tachodata.ddd | ./dddparser -vu | jq '[.vu_activities_1[].vu_driver_activity_daily_records[].activity_daily_presence_counter]'

# Pretty print and page through output
cat tachodata.ddd | ./dddparser -vu | jq . | less

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