Re: bash displays strange characters after base64 decoding

[Bob Proulx]

Valentin Schmidt wrote:
> Subject: bash displays strange characters after base64 decoding
> Bash displays strange characters (including command prompt) (see attached
> png file) after the execution of the base64 (GNU coreutils 8.21) command
> like described as follows:
> base64 -d base64.txt

This is not related to your command shell bash.  It is only your
terminal that is involved.  Your terminal interprets escape sequences.
Move the cursor.  Change the color.  Use reverse video.  Use a
different character set.  Things like that.

You have sent random binary characters to your terminal.  This is
similar to if you decided to eat random non-food items from random
shelves in a store.  Newspapers.  Shampoo.  Sunscreen.  Things like
that.  It won't be good for you!  Eventually you will eat something
that will upset your tummy and send your body into a bad state.  Not
good!

Sending random binary characters to your terminal is similar to this.
It is not good for your terminal.  With enough random characters it is
inevitable that you will eventually send your terminal something that
will instruct it to go into an undesirable state such as you have
shown.

> The aim was actually to direct the output of the base64 command into a file
> (would have been a .jpg file) but the ">decoded.jpg" was forgotten.

Oops. :-(

> Accordingly the output was directed to stdout instead. This resulted in the
> command prompt consisting of strange characters after decoding.

That is unfortunate.  However terminals are called "smart terminals"
for the reason that they interpret escape sequences.  Because this is
useful for them to do this.  There are "dumb terminals" available too.
Dumb terminals do not interpret escape sequences and would be safe
from this problem.  Except people generally do not like dumb terminals
because they do not have any of the useful capabilities we have come
to like.  Other than switching to a dumb terminal there is little that
can be done to prevent this.  Other than avoiding feeding your
terminal random binary characters.

> Also any command entered via the keyboard resulted in strange characters
> being displayed instead of the typed characters.
> Also the output of the ls (which seems to be executed) command (as an
> example) is displayed as strange characters.

I don't recognize the terminal emulator program you are using.  One of
the menu options may offer a way to reset it.  Otherwise you can try
the reset command to reset the terminal back to a sane state.

  man reset

       When invoked as reset, tset sets cooked and echo modes, turns
       off cbreak and raw modes, turns on newline translation and
       resets any unset special characters to their default values
       before doing the terminal initialization described above.  This
       is useful after a program dies leaving a terminal in an
       abnormal state.  Note, you may have to type

           <LF>reset<LF>

       (the line-feed character is normally control-J) to get the
       terminal to work, as carriage-return may no longer work in the
       abnormal state.  Also, the terminal will often not echo the
       command.

Otherwise the best you can do is to close the terminal and start a new
one.

Bob