NFCShell

Writing
Use an app like NFCTools to write a raw data record with the mime tag text/sh. You can also use ZLIB compression if you need to compress your script.

Scanning
The app has no foreground screen. An NFC intent will trigger NFCShell to open a background thread, which executes your script.

Notes
There is no script output.
Your working directory is /sdcard/Android/data/id/files, /sdcard/Android/data/id/cache, or /data/data/id/files depending on what is available.