ncdump-json — JSON (and CDL) output for netCDF

A modification of ncdump (netCDF 4.1.1) that adds JSON output.

If you omit -j, it behaves exactly like the original ncdump.

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Table of contents

• Features
• Quick start
• Usage
• Examples
• Run with Docker
• Install from source
• Platform notes
• Support & maintenance
• Contributors & license

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Features

• Drop-in replacement for ncdump; use -j to emit JSON.
• Streams to stdout; easy to pipe into other tools.
• Familiar ncdump options work as expected (e.g., -h, -v var1,var2).
• Tested with netCDF 4.1.1.

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Quick start

Headers to JSON

ncdump-json -h -j tests/socib-buoy.nc

Variable values to JSON

ncdump-json -v AIRT -j tests/socib-buoy.nc

Without -j, output is standard CDL—just like ncdump.

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Usage

ncdump-json [options] file.nc

Options (common with ncdump):
  -h            # header only
  -v var1,...   # restrict to variables
  -j            # JSON output (otherwise CDL)

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Examples

JSON header

$ ncdump-json -h -j tests/socib-buoy.nc
{"dimensions":{"time":3169},"variables":{"time":{"type":"double","dimensions":["time"],"attributes":{"standard_name":"time","units":"seconds since 1970-01-01 00:00:00","long_name":"time","_FillValue":-99999.9000000000,"axis":"T","calendar":"gregorian"}},"AIRT":{"type":"double","dimensions":["time"],"attributes":{"standard_name":"air_temperature","units":"C","long_name":"air temperature","_FillValue":-99999.9000000000,"coordinates":"time","valid_min":-15.0000000000000,"valid_max":45.0000000000000,"original_units":"C","observation_type":"measured","precision":"0.01"}},"QC_AIRT":{"type":"byte","dimensions":["time"],"attributes":{"long_name":"quality flag for air_temperature","quality_control_convention":"SOCIB Quality control Data Protocol","valid_min":0,"valid_max":9,"_FillValue":10,"flag_values":[0,1,4,9],"flag_meanings":"no_qc_performed good_data bad_data
...

JSON values for a variable

$ ncdump-json -v AIRT -j tests/socib-buoy.nc
{"AIRT":[17.06,null,17.43,16.51,15.22,16.51,15.22,15.32,14.49,16.88,15.96,16.14,15.77,16.6,15.78,16.6,16.05,15.96,16.51,16.97,17.06,15.41,14.95,14.58,14.95,14.03,14.31,14.03,13.21,13.02,13.21,13.02,12.75,12.48,12.29,12.2,11.84,11.75,11.93,11.75,11.2,11.02,11.02,11.02,10.65,10.47,10.65,10.47,10.2,10.02,10.02,9.93,9.75,9.65,9.56,9.65,9.47,9.2,9.11,9.11,9.11,9.29,9.29,9.2,9.11,9.11,8.57,8.84,8.75,8.57,8.66,8.57,9.02,8.75,9.02,9.29,9.11,9.47,9.11,8.93,8.57,8.48,8.3,8.39,8.3,8.21,7.93,8.21,7.93,8.39,7.93,8.39,8.57,8.39,8.48,8.57,8.3,8.3,8.21,8.39,8.21,8.75,9.2,9.47,9.75,9.47,9.56,9.65,9.56,9.56,9.47,9.56
...

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Run with Docker

No toolchain needed. Works on Linux, macOS, and Windows 10+.

1. Install Docker: https://docs.docker.com/get-docker/
2. Clone or download this repository
3. Build the image:

docker build -t ncdump-json .

4. Test:

docker run -it --rm ncdump-json -j tests/socib-buoy.nc

5. Use with your own file (mount current dir):

docker run -it --rm -v "$PWD:/data" ncdump-json -j /data/myfile.nc

Note (paths): On Windows, Docker volume paths use Windows conventions. Mount the folder containing your .nc file and reference it inside the container (e.g., -v "C:\path\to\data:/data" then use /data/file.nc).

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Install from source

Download the latest release: https://github.com/jllodra/ncdump-json/releases

Dependencies:

• cmake
• libnetcdf-dev
• pkg-config

Build:

cd ncdump-json
cmake .
make          # warnings may appear; that’s okay
sudo make install   # installs binary to /usr/local/bin

Run tests (optional):

cd tests
./run_tests.sh

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Platform notes

• Works (tested) on Linux and macOS.
• Debian/Ubuntu: see this comment for package specifics: #16 (comment)
• FreeBSD: see: #17

Please check existing Issues before opening a new one.

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Support & maintenance

This project is not actively maintained. I’m grateful for the emails and issues and try to reply when I can, but I left SOCIB in 2012.

If your work depends on this tool and you need help or enhancements, feel free to reach out via e-mail and we’ll discuss options:

Josep Llodrà – jlg.hrtc@gmail.com

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Contributors & license

Thanks to everyone who has submitted issues and pull requests—your help keeps this useful for others.

Contributors: https://github.com/jllodra/ncdump-json/graphs/contributors

Upstream netCDF copyright and license: http://www.unidata.ucar.edu/software/netcdf/copyright.html

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