Why did my bash prompt turn to gibberish after I accidentally ran `cat` on a .coverage file?

Question

I had just installed coverage and run it a few times when I noticed a .coverage file hanging around in my repo, which is -- according to the file utility -- a 8086 relocatable (Microsoft) file. And then I did this, because I had no idea what it was and wanted to know what was inside it...

~/repos/personalsite(master 7↑)$ cat .coverage
...lots of output...
≤☃─☃┼±@≤⎽☃└:·/⎼e⎻⎺⎽/≤☃─☃┼±⎽☃└↓c⎺└/≤☃─☃┼±⎽☃└(└▒⎽├e⎼ 7↑)$ 

Even when I pressed Enter a couple times it remained like that. Not only that, when I typed into the command line, characters that I didn't expect showed up, e.g.

$ ↓┘ ┼⎺├ ⎺┼┌≤ ├▒▒├┬▒≤ ☃⎽ ├▒e⎼e ┼⎺├

The only solution was for me to close the (tmux) window. I'm just wondering (a) why this happened, and (b) if there's any way to fix this next time I happen to do this?

Answer 1

For question a): this depends on which type of terminal you have. Just do a echo $TERM to see which type of terminal you have. xterm should be fine. I had this problem a lot when connecting via serial console and the only working type of terminal was vt100 (an old but very compatible terminal). Also when changing $TERM to vt100 via SSH I had the same problem.

for question b): executing the command reset should do the trick. Maybe you see the command also in gibberish but it should work.

Just for clarification: this happens every time you try to do cat on a binary encoded file, not specially .coverage files.

Answer 2

The literal character ^N can cause this behavior on certain terminals when printed. cat printed that character when trying to read the binary encoded file.

To reproduce this behavior, you can write the ^N character to a file using literal character entry in vi. Open vi, enter Ctrl-vCtrl-n in insert mode, and save the file. If you cat this file, your terminal's encoding will be borked.

The literal character ^O reverses this behavior, and can be written in vi by entering Ctrl-vCtrl-o.