On Debian 13 `echo -n test | qrencode -t UTF8` generates the attached QR code, however `zbarimg` *scanned 0 barcode symbols*. I suspect the diamond characters to be to blame, how to solve my QR code generation/scanning issue?
Jul 26, 3:40pm

The issue you're encountering is likely due to the character encoding and terminal/console font limitations when generating a QR code in UTF-8 text mode (-t UTF8) with qrencode. The diamond characters (◊, ♦, etc.) are often used as placeholders for unsupported or misinterpreted UTF-8 characters in terminals, which can break the QR code's structure and make it unscannable.

Root Cause

  1. Terminal Font Support:

    • The UTF-8 output of qrencode relies on block characters (e.g., █, ▀, ▄, etc.) to represent the QR code. If your terminal font does not support these characters, they may render as diamonds or other placeholder symbols.
    • zbarimg expects a visually accurate representation of the QR code to scan it. If the characters are replaced or corrupted, the QR code becomes invalid.

  2. UTF-8 Interpretation:

    • The -t UTF8 flag outputs the QR code as text using Unicode block elements. If the terminal or the file where the output is saved does not handle UTF-8 correctly, the QR code will not render properly.

Solutions

1. Use a Different Output Format

  • Instead of UTF-8 text, generate the QR code in a graphical format (e.g., PNG, SVG) that zbarimg can reliably scan.
  • Example: 
    bash
    echo -n "test" | qrencode -t PNG -o qrcode.png
zbarimg qrcode.png
  • This avoids terminal font issues entirely.

2. Ensure Terminal Font Supports Block Characters

  • Use a font that supports Unicode block elements (e.g., DejaVu Sans Mono, Noto Mono, or GNU FreeFont).
  • Test if your terminal can display block characters correctly: 
    bash
    echo -e "\u2588\u2584\u2580"
    If you see solid blocks (█, ▄, ▀), your font supports them. If not, switch to a compatible font.

3. Use ANSI or ASCII Output

  • If you must use text output, try -t ANSI or -t ASCII instead of UTF-8: 
    bash
    echo -n "test" | qrencode -t ANSI
  • ANSI/ASCII uses simpler characters that are more widely supported, though the QR code may look less "crisp."

4. Pipe to a File and Inspect

  • Save the UTF-8 output to a file and inspect it for corruption: 
    bash
    echo -n "test" | qrencode -t UTF8 > qrcode.txt
cat qrcode.txt
  • If the file contains diamond characters, the issue is with the terminal or shell's UTF-8 handling.

5. Use qrencode with -s (Size) for Better Readability

  • Increase the size of the QR code to make block characters more distinct: 
    bash
    echo -n "test" | qrencode -t UTF8 -s 2

6. Alternative Tools

  • If qrencode continues to cause issues, try alternative QR code generators like:
    • qr (from the qr package)
    • Online tools (for testing)
    • Python libraries (qrcode, pyqrcode)

Recommended Fix

Use PNG output for reliability:

bash
echo -n "test" | qrencode -t PNG -o qrcode.png && zbarimg qrcode.png

This bypasses terminal font issues and ensures zbarimg can scan the QR code correctly.

Jul 26, 3:40pm

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