>```
>RUN source /root/.nvm/nvm.sh \
>    && node -p "crypto.randomBytes(32).toString('base64')" > key.txt
>
>#RUN sed -ie "s/somelongsecretstring/$(cat key.txt)/g" steem-dev.json
>
>## Warning, big hack, if you can figure out how to get that sed command above to work
># let me know
>RUN sed -ie 's/somelongsecretstring/KrddWYj8wPonvIpjfNvNyJiw8RfVyOfvEaeXcWeOMHI=/g' steem-dev.json
>```

I guess the tricky part is that `/` is a valid character in a base64 string, so if there is a `/` is in key.txt,  the `sed` command sometimes won't work. Try this:
```
RUN sed -ie "s#somelongsecretstring#$(cat key.txt)#g" steem-dev.json
```