Bash script to accept password and replace characters with * as they are typed

ta0kira · 09-30-2011, 06:36 AM

This seems like a lot of work for the objective. What about this:

Code:

#!/bin/bash


unset PWORD
PWORD=

echo -n 'password: ' 1>&2


while read -n1 -s char; do

  case "$( echo -n "$char" | od -An -tx1 )" in

    '')
      break
    ;;

    ' 7f')
      if [ -n "$PWORD" ]; then
        PWORD="$( echo "$PWORD" | sed 's/.$//' )"
        echo -n $'\b'' '$'\b' 1>&2
      fi
    ;;

    *)
      PWORD="$PWORD$char"
      echo -n '*' 1>&2
    ;;

  esac

done


echo
echo $PWORD

Kevin Barry

A.Thyssen · 10-02-2011, 11:22 PM

The last script is not too bad.

You need to include the IFS= or the password read will abort on space or tab. Also add a -r option, otherwise a backspace at the end will escape the final newline. (A real painful bash default).

I would also include ' 08' (backspace) for character removal and ' 15' (^U or kill line)
to restart the password. But otherwise it is quite good.

Code:

  ' 15') # ^U or kill line
        echo -n "$PWORD" | sed 's/./\cH \cH/g' >&2
        PWORD=''
        ;;

NOTE that sed assumes GNU-sed.
If this could be a problem another alternative is

Code:

      echo -n "$PWORD" | tr -c '\b' '\b' >&2
      echo -n "$PWORD" | tr -c ' '  ' '  >&2
      echo -n "$PWORD" | tr -c '\b' '\b' >&2

All it needs now is for it to not do prompt and star processing when the input is not a TTY! (just a straight pass-thru) and you have a simple (no-gui, no-curses) password reader.

Note if you know the input is from a TTY and wanted a "curses" version try "dialog"

Code:

   dialog --stdout --insecure --passwordbox  "Password:" 0 0

The --stdout causes the password out stdout and curse output to go direct to the TTY

This method like most GUI interfaces will not let you input TAB's.

A.Thyssen · 01-18-2018, 12:02 AM

Continuing this discussion...

http://www.ict.griffith.edu.au/antho...sswd_input.txt

Related to this is the final script as a TTY password input helper...

http://www.ict.griffith.edu.au/antho...#askpass_stars

I have since discovering the linux systemd command "systemd-ask-password"
this is almost perfect for this sort of things, though was not designed for TTY input but for use during computer startup (read password for encrypted disk drive mounting, or computer unlocking).

I also took this problem further, and looks at the temporary caching of passwords for use in things like editing encrypted files, when the same password used to decrypt the file, is later used to re-encrypt the file, and prevent possible mishaps of mistyping the password twice during the re-encryption process.
See

http://www.ict.griffith.edu.au/antho...wd_caching.txt