Download Sessions via Script

If you need to download many sessions at once — a whole project, or a long list of specific sessions — the Download Images button on the Project page in CNDA works, but it's built for downloading a handful of sessions at a time through your browser. For many sessions or sessions of a large size, use the CNDA Bulk Download script instead.

It logs into CNDA for you, downloads each session as a .zip, skips anything it already downloaded, retries a failed download once automatically, and keeps a log of everything it did.

This page walks Windows users all the way from "I have nothing installed" to a finished download. Mac and Linux users already have everything the script needs and can skip to step 4.

Instructions

  1. If you only need a few sessions, use Downloading Sessions From CNDAopen in new window instead — it's faster for a small number of sessions and doesn't require any of the setup below.

  2. Download the script file: cndaBulkDownload.sh. Right-click the link and choose Save link as..., then save it somewhere you'll remember — your Desktop or Documents folder works well. Note: your browser may warn you that .sh files can be harmful. This is a standard warning for any script file, not specific to this one — click Keep if prompted.

  3. Install Git Bash (Windows only, one-time setup). This gives Windows the command-line tools (bash, curl) the script needs, which aren't included by default.

    1. Go to https://git-scm.com/download/winopen in new window — the download starts automatically. If it doesn't, click the "Click here to download" link on that page.
    2. Once downloaded, double-click the installer file (something like Git-2.xx.x-64-bit.exe) to run it.
    3. Windows may show a "Do you want to allow this app to make changes to your device?" prompt — click Yes.
    4. Click through the installer screens. The default settings on every screen are fine for this script — just click Next on each one, then Install on the final screen.
    5. When it finishes, click Finish. Note: if your team already has WSL (Windows Subsystem for Linux) set up on your machine, you can use that instead of Git Bash — open your Linux distro from the Start menu and follow the same steps below. If you're not sure whether you have WSL, Git Bash is faster to get running and is all this script needs.

  4. Open a command line.

    • Windows: click the Start menu, type Git Bash, and click Git Bash in the results. A dark window with a text prompt opens — this is your command line for every step below.
    • Mac: press Cmd + Space, type Terminal, and press Enter.
    • Linux: open your distro's terminal application from your applications menu.

  5. Go to the folder where you saved the script. Type cd followed by the folder path. For example, if you saved it to your Desktop:

    cd ~/Desktop

    or if you saved it to Documents:

    cd ~/Documents

    Note: in Git Bash, ~ always means your Windows user folder (C:\Users\yourname), so ~/Desktop and ~/Documents work the same way they do on Mac and Linux. If you saved the script somewhere else, like a Downloads folder or a specific project folder, use that path instead — for example cd ~/Downloads or cd "/c/Users/yourname/My Folder". Tip: you can also type cd (with a trailing space) and then drag the folder from File Explorer directly into the Git Bash window — it will fill in the correct path for you automatically.

  6. Confirm the script is actually there before continuing:

    ls cndaBulkDownload.sh

    If it prints back cndaBulkDownload.sh, you're in the right folder. If you instead see No such file or directory, you're either in the wrong folder or the file didn't save with that exact name — check step 5 and step 2 again.

  7. Make the script runnable. This is a one-time step per computer:

    chmod +x cndaBulkDownload.sh

    You won't see any output from this — that's expected. It only needs to be done once; you don't need to repeat it the next time you use the script on the same computer.

  8. Run the script. You have two ways to tell it what to download:

    Download an entire project

    ./cndaBulkDownload.sh -u yourUsername -p MRF_1234

    Replace yourUsername with your CNDA username and MRF_1234 with the actual project ID. You'll be prompted to type your CNDA password — it won't show anything on screen as you type, not even dots. This is normal terminal behavior, not a freeze. Type it and press Enter.

    Download a specific list of sessions

    Create a CSV file listing the sessions first — see Session List CSV Format below — then run:

    ./cndaBulkDownload.sh -u yourUsername -s mysessions.csv

    Note: use one or the other, not both — the script will stop with an error if you pass -p and -s together.

  9. (Optional) Choose where files are saved. By default, downloads go into a new folder named after the project (or cnda_downloads if you used a session list), created inside whatever folder you were in when you ran the script. To pick your own folder instead, add -d:

    ./cndaBulkDownload.sh -u yourUsername -p MRF_1234 -d /path/to/my/folder

  10. (Optional) Avoid typing your password every time. For a long-running download, or if you're downloading several projects back to back, you can save your credentials to a file instead of using -u:

    1. In the same folder as the script, create a plain text file named creds.json containing exactly this, with your own username and password:
      {"user": "yourUsername", "password": "yourPassword"}
    2. Run the script with -c instead of -u:
      ./cndaBulkDownload.sh -c creds.json -p MRF_1234

    Note: this file holds your password in plain text. Restrict who can read it (chmod 600 creds.json), never commit it to Git, never email it, and delete it when you're done with it. Do not use -u and -c together — the username comes from the file.

Session List CSV Format

If you're downloading specific sessions instead of a whole project, create a plain CSV file — you can build this in Excel and use Save As → CSV, or write it directly in a plain text editor. No header row — just one session per line, in this order: Project,Subject,Session

MRF_1234,Subj001,Subj001_MR1
MRF_1234,Subj002,Subj002_MR1
CCIR_5678,Subj010,Subj010_MR2

What Happens While It Runs

You'll see output scroll by that looks like this:

[1]
Downloading Subj001_MR1 (MRF_1234/Subj001)...
[2]
Subj002_MR1.zip already exists, skipping

When it finishes, you'll see a summary line:

Done. OK=42  FAIL=1  SKIP=3
See /path/to/logs/cndaBulkDownload_20260803_143000.log for details.
  • OK — successfully downloaded.
  • SKIP — already downloaded in a previous run; left alone.
  • FAIL — something went wrong with that specific session. Open the log file named in that line for details on exactly which session and why.

Note: if anything fails, it's almost always safe to just run the exact same command again. The script automatically skips everything it already downloaded successfully, so a rerun only retries what actually failed.

Troubleshooting

  • command not found: ./cndaBulkDownload.sh — you're either not in the same folder as the script, or you forgot step 7 (chmod +x). Run ls cndaBulkDownload.sh to check you're in the right place.
  • "Your access is probably not enabled for this project, or the project id is wrong." — double-check the project ID is typed exactly as it appears in CNDA, and confirm you have access to that project.
  • "CNDA login failed. Check your credentials and retry." — your username or password was entered incorrectly. Just run the command again.
  • A session fails every time, even after rerunning — check the log file named in the "Done." summary line for the specific reason next to that session.
  • You're not sure if you're signed in for too long — CNDA sessions expire automatically after a period of inactivity. The script detects this on its own and re-logs in for you mid-run; you don't need to do anything.