bash Cookbook

Prompting for a Password

Problem

You need to prompt the user for a password, but you don’t want it echoed on the screen.

Solution

read -s -p "password: " PASSWD
printf "%b" "\n"

Discussion

The -s option tells the read command not to echo the characters typed (s is for silent) and the -p option says that the next argument is the prompt to be displayed prior to reading input.

The line of input that is read from the user is put into the environment variable named $PASSWD.

We follow read with a printf to print out a newline. The printf is necessary because read -s turns off the echoing of characters. With echoing disabled, when the user presses the Enter key, no newline is echoed and any subsequent output would appear on the same line as the prompt. Printing the newline gets us to the next line, as you would expect. It may even be handy for you to write the code all on one line to avoid intervening logic; putting it on one line also prevents mistakes should you cut and paste this line elsewhere:

read -s -p "password: " PASSWD ; printf "%b" "\n"

Be aware that if you read a password into an environment variable it is in memory in plain text, and thus may be accessed via a core dump or /proc/core. It is also in the process environment, which may be accessible by other processes. You may be better off using certificates with SSH, if possible. In any case, it is wise to assume that root and possibly other users on the machine may gain access to the password, so you should handle the situation accordingly. ...