Shell Programming and Scripting

#!/bin/bash

# script to change a password
username ()

{
while :
do
echo "please enter a username"
read user
grep -iq "$user" usernames
a=$?
echo "please enter pin"
read pin
grep -i "^$user" usernames | grep -q "$pin$"
b=$?

if [ $a -eq 0 -a $b -eq 0 ]
then
echo "Welcome"
change1
break
else
echo "Please try again"
fi
done
}


change1 ()
{
echo "please enter a new password"
read npass

sed 's/$pin/$npass/' usernames
echo "here are your logon details"
sed -n '/^$user/p' usernames
return
}

username

#!/bin/bash

Username        Password

John    123
Dan     345
Matt    678

sed '<some operations>' /path/to/input > /path/to/output
mv /path/to/output /path/to/input

$ openssl passwd -salt Xx -crypt 1234
Xx7LFoJpR7vp.

#!/bin/bash
# script to change a password
username() {
while :
do
   read -p "please enter a username: " user
   ln=$(grep "^$user" usernames)
   pass=${ln#* }
   salt=${pass:0:2}
   if [ "$(openssl passwd -salt ${salt:-XX} | sed 's/\r//')" = "$pass" ]
   then
      echo "Welcome $user"
      break
   else
      echo "Password incorrect - please retry"
      echo
   fi
done
}
change1 () {
    new=$(while ! openssl passwd ; do echo "try again
">&2; done)
    sed -i "s:^${user} .*:${user} ${new}:" usernames
}
username
change1