Entering passwords

[Derek Card]

Hello Guys,

I need to prompt the users for passwords without anyone being able to see it? Is there an easy way to do this in a shell script?

TIA, Derek

[A. Clay Stephenson · Accepted solution]

Hi Derek:

Yes, it's quite easy.

#!/usr/bin/sh

trap 'stty echo; exit' 0 1 2 3 15


echo "Enter Password: \c"
stty -echo
read PASSWD
stty echo

I should add that the trap command is really not optional. You see, the stty command alters the tty device, not just your script. Any subsequent processes would also have the echo turned off if you exited in the -echo state. The trap, insures that the terminal is restored upon exit even via a Ctrl-C (or whatever your n'rupt is set to).

I suggest that you comment out the trap statement and do a ctrl-c when entering the password and you will see just what I mean.



Regards, Clay

P.S. You should have been able to find this yourself with that little button.

[Derek Card]

Thanks, that worked a treat. I would like to add a feature to have the screen display a "*" as each letter is typed.

TIA, Derek

[A. Clay Stephenson]

That's a bit more difficult and I wouldn't do it from the shell. You have to disable the terminal's line-orieted discipline. It's generally not practical to do character by character entry from the shell. I'm not saying it can't be done but rather the possible negative consequences outweigh the rather limited gains. If I'm going to do this, I use C or Perl (and I don't like to use Perl for this either). From the shell, you can use dd with a bs=1 and count=1 but it's not pretty.

[Derek Card]

Hello again guys,

I have one last related question. Is there a way in unix to clear the screen? to place the cursor at a certain location? I know I need to echo some kind of character sequence.

TIA, Derek

[A. Clay Stephenson]

Well, the character sequence is dependent upon the type of terminal. This is set by the TERM variable. When that is set and exported, you can use the "tput" command.

e.g.

tput cup row column
positions the cursor.

tput clear
clears the screen.

Tput looks up these sequences in the terminfo database and instantiates them if the sequence is defined.

Man tput and terminfo for details.

Clay