cat on binary: garbles stdout chars, wastes terminal

jhwilliams · 07-17-2007, 02:50 PM

This is more of an "I'm curious why" question... in regards to a command like this:

Code:

$ cat /bin/vi

Strange things happen. The console prompt becomes garbled nonsense. This phenomenon is not unique to vi, either; many binaries have this effect on standard out when cat'ed.

Why does this happen - are bits of the binary being executed? But if this is so, why is the file not executed properly? Lastly, is there anyway to safeguard the cat command from this sort of thing?

macemoneta · 07-17-2007, 02:57 PM

Terminal programs emulate real hardware, like vt100 (which was an actual device) and xterms. These devices respond to control characters - binary values that do not represent alphanumeric characters - by performing special functions. This is what causes the result you see.

You can usually correct the problem by running the command 'reset' (even if you can't see what you are typing, just type it and hit enter).

There is no need to 'safeguard' the cat command, as no damage is done. Rather than directly using cat on binaries, you probably want to use strings to extract human readable information:

cat /bin/vi | strings | less

You can determine the type of file by using the file command:

file /bin/vi

GregLee · 07-17-2007, 03:10 PM

Also, you can "vi /bin/vi" to look inside (if "vi" is vim, anyway).

marozsas · 07-17-2007, 03:55 PM

you can filter out binary values without a character representation and display only the strings.
This is nice to find hidden strings in the binary program

Code:

cat /bin/vi | strings

or more directly,

Code:

strings /bin/vi