Parsing text in BASH - bash

Question

I have a username system. The user picks a username, password and pin number and this is saved into UPP.db. I want to be able to parse this text so that a user can either be edited (Change password) or Deleted (Remove Line). I have coded a solution for both but both return me with an error and jump to the "Else" part of my If statement. I will provide the code for the edit section as the delete is pretty similar and would be redundant providing both.
echo "Please enter the username you wish to edit"
read usernamecheck
usernamesearch=$( grep $usernamecheck\$ UPP.db | cut -d" " -f1 )
if [ $usernamecheck = $usernamesearch ]
then
echo "Please enter $usernamesearch PIN"
read pincheck
pinupdate=$( grep $pincheck\$ UPP.db | cut -d" " -f3 )
if [[ $pin = $pinupdate && $usernamecheck = $usernamesearch ]]
then
echo "The user `grep "$pin"\$ UPP.db | cut -d" " -f1`'s password is about to be changed "
echo "Please enter the new password"
read newpass
passwordcheck=$( grep $pincheck\$ UPP.db | cut -d" " -f2 )
sed -i "s/$passwordcheck/$newpass/g" UPP.db
echo "Password changed"
else
echo "The PIN is incorrect"
fi
else
echo "This username is not reconised"
fi
;;

Answer 1

string equality comparisons will be more precise than regular expressions. Here, I use awk not grep to enable that. You might want to keep the bash man page handy while you read this.
read -p "Please enter the username you wish to edit: " usernamecheck
# extract all the fields at once
read -r db_user db_pass db_pin < <(
awk -v name="$usernamecheck" '$1 == name {print; exit}' UPP.db
)
if [[ -z $db_user ]]; then
echo "This username is not reconised"
else
read -p "Please enter $db_user PIN: " pincheck
if [[ "$db_pin" != "$pincheck" ]]; then
echo "The PIN is incorrect"
else
echo "Changing password for user $db_user:"
while true; do
read -s -p "Please enter the new password: " newpass
echo
read -s -p "Please re-enter the new password: " newpass2
echo
if [[ "$newpass" == "$newpass2" ]]; then
break
fi
echo "Passwords do not match. Try again."
done
ln UPP.db "UPP.db.$(date "+%Y%m%d%H%M%S")" # create a backup copy
temp=$(mktemp)
# update the password
awk -v newpw="$newpass" -v name="$db_user" '
$1 == name {$2 = newpw}
{print}
' UPP.db > "$temp" && mv "$temp" UPP.db
echo "Password changed"
fi
fi
Style tip: in an if-else-end construct, put the smaller block first, then the else-block is close to the condition. Aids readability.
If this plain text file, containing user passwords, is anywhere close to the internet, you're f*cked.