dd if=/dev/s<TAB> not run correctly

[andychu]

2 bugs here:

• bash --rcfile /dev/null DOES complete this by default
• osh --rcfile /dev/null does NOT

Also

• bash-completion has some logic for it
• OSH doesn't run it correctly, it replaces if=/dev/s with /dev, rather than if=/dev/s

inspired by https://twitter.com/n_copa/status/1380569611830169601