cat > $HOME/.doBASH.sh << EOF
#!/bin/bash
# REV02: Tue 27 Jun 2023 15:00
# START: Fri 16 Jun 2023 16:00
# .doBASH.sh

readlink -- /bin/sh
[[ "$(readlink -- /bin/sh)" == "/bin/bash" ]] || { /bin/rm -f /bin/sh; ln -s /bin/bash /bin/sh; }
readlink -- /bin/sh
exit
EOF
### #####

cat > $HOME/.doDNS.sh << EOF
#!/bin/bash
# REV04: Sun 10 Sep 2023 10:00
# REV03: Wed 16 Aug 2023 09:30
# REV02: Tue 27 Jun 2023 16:00
# START: Fri 16 Jun 2023 16:00
# .doDNS.sh

RESOLV="/etc/resolv.conf"

echo   "===== \$RESOLV was:"
cat    \$RESOLV
cat >  \$RESOLV <<< "nameserver 8.8.8.8"
cat >> \$RESOLV <<< "nameserver 1.1.1.1"
cat >> \$RESOLV <<< "nameserver 8.8.4.4"
echo   "===== \$RESOLV now:"
cat    \$RESOLV
EOF

cat > $HOME/.doZERO.sh << EOF
#!/bin/bash
# REV03: Sun 10 Sep 2023 15:00
# REV02: Tue 27 Jun 2023 16:00
# START: Fri 16 Jun 2023 16:00
# .doZERO.sh

rm -f /tmp/tmptmp
df -h /
dd if=/dev/zero of=/tmp/tmptmp bs=1M
df -h /
echo "==="
rm -f /tmp/tmptmp
df -h
sync

exit
EOF
### #####

cat > $HOME/.doUPDATE.sh << EOF
#!/bin/bash
# REV01: Wed 16 Aug 2023 07:30
# START: Wed 16 Aug 2023 07:00
# .doUPDATE.sh

time (
  aptitude update          &&
  echo " ===== 1 ====== "  &&
  aptitude safe-upgrade -y &&
  echo " ===== 2 ====== "  &&
  aptitude autoclean -y;
)

exit
EOF
### #####

who am i

cd

pwd

ls -al .do*

# To set symbolic link from /bin/sh to /bin/bash (account: root)
[ -f .doBASH.sh ] && bash .doBASH.sh

# To alter DNS Servers (account: root)
[ -f .doDNS.sh ] && bash .doDNS.sh

# Clean HardDisk by filling zero (account: root)
[ -f .doZERO.sh ] && bash .doZERO.sh

# Update Debian (account: root)
[ -f .doUPDATE.sh ] && bash .doUPDATE.sh