How to create a Password Protected Directory using linux command prompt?

Create a .htaccess file in the folder you want to set.
like:
#root@adu [/home/hostsite/public_html/admin]# vi .htaccess
copy and paste the following lines:
———————————————————-
AuthName “Secure Area”
AuthType Basic
AuthUserFile /home/hostsite/public_html/admin/.htpasswd
require valid-user
———————————————————-
Now set a password:
#htpasswd -c .htpasswd admin
New password: admin321
confirm password: admin321

You are done. test it: http://www.hostsite.com.au/admin and enter user name as admin and password as admin321

Change password shell script

#!/usr/local/bin/expect -f
# Password change shell script, tested on Linux and FreeBSD
# ----------------------------------
# It need expect tool. If you are using Linux use following command
# to install expect
# apt-get install expect
# FreeBSD user can use ports or following command:
# pkg_add -r -v expect
# ----------------------------------
# If you are using linux change first line
# From:
#!/usr/local/bin/expect -f
# To:
#!/usr/bin/expect -f
# -----------------------------------------------
# Copyright (c) 2006 nixCraft project
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------
# display usage
if {$argc!=2} {
   send_user "usage: $argv0 username password \n"
   exit
}
# script must be run by root user
set whoami [exec id -u]
if {$whoami!=0} {
   send_user "You must be a root user to run this script\n"
   exit
}
#
set timeout -1
match_max 100000
# stopre password
set password [lindex $argv 1]
# username
set user [lindex $argv 0]
# opem shell
spawn $env(SHELL)
# send passwd command
send -- "passwd $user\r"
expect "assword:"
send "$password\r"
expect  "assword:"
send "$password\r"
send "\r"
expect eof