The following script will upload a file to the WonderSwan using XMODEM through lrzsz:

  #!/bin/sh
  stty -F "$2" 38400 cs8 raw -echo
  lrzsz-sx -X "$1" < "$2" > "$2"
  

Usage: ./upload.sh file.bin /dev/ttyACM0

The following script will download a file from the WonderSwan using XMODEM through lrzsz:

  #!/bin/sh
  stty -F "$2" 38400 cs8 raw -echo
  lrzsz-rx -X "$1" < "$2" > "$2"
  

Usage: ./download.sh file.bin /dev/ttyACM0