diff --git a/zsh.sh b/zsh.sh
index 0dbe403..6661b5c 100755
--- a/zsh.sh
+++ b/zsh.sh
@@ -1,15 +1,17 @@
 #!/usr/bin/bash
 
 # Detect fish shell and ask user to switch to bash (bash-only syntax)
-if [ -n "${FISH_VERSION:-}" ] || case "$SHELL" in *fish*) ;; *) false ;; esac; then
+if [ -n "${FISH_VERSION:-}" ] || case "${SHELL:-}" in *fish*) ;; *) false ;; esac; then
   echo "Warning: fish shell detected."
   echo "This script is written for bash and may have syntax issues under fish."
   echo "Please switch to bash first and re-run it, e.g.: bash $0"
+  if [ -t 0 ] && [ -e /dev/tty ]; then
   read -r -p "Press Enter to continue anyway, or Ctrl+C to cancel..." </dev/tty || true
 fi
+fi
 
 skip_watermark=false
-if [ "$1" = "--skip-watermark" ]; then
+if [ "${1:-}" = "--skip-watermark" ]; then
     skip_watermark=true
 fi
 
@@ -34,8 +36,8 @@ echo "This script will backup your current zsh config if it exists "
 # Enable exit on error
 set -eu
 
-# Install prerequisites if installed skips
-if ! command -v zsh >/dev/null && command -v git >/dev/null && command -v curl >/dev/null && command -v fzf >/dev/null; then
+# Install prerequisites if any of them is missing
+if ! command -v zsh >/dev/null || ! command -v git >/dev/null || ! command -v curl >/dev/null || ! command -v fzf >/dev/null; then
   if command -v pacman >/dev/null; then
     echo "pacman detected. Installing prerequisites"
     sudo pacman -S zsh git curl fzf --noconfirm
@@ -47,7 +49,13 @@ if ! command -v zsh >/dev/null && command -v git >/dev/null && command -v curl >
   fi
 fi
 
-zsh=$(which zsh)
+if ! command -v zsh >/dev/null; then
+  echo "error: zsh could not be installed (no supported package manager, or install failed)." >&2
+  echo "Install zsh manually, then re-run this script." >&2
+  exit 1
+fi
+
+zsh=$(command -v zsh)
 
 # Do not print commands
 set +x
@@ -70,30 +78,44 @@ set -eu
 # Do not print commands
 set +x
 
+# Backup the user's current config before oh-my-zsh overwrites it
+if [ -f "$HOME/.zshrc" ]; then
+  if ! cp "$HOME/.zshrc" "$HOME/.zshrc.bak"; then
+    echo "error: failed to back up $HOME/.zshrc to $HOME/.zshrc.bak" >&2
+    exit 1
+  fi
+  echo "Backed up $HOME/.zshrc to $HOME/.zshrc.bak"
+fi
+
 # Install oh-my-zsh without entering zsh
-CHSH=no sh -c "$(curl -fsSL https://raw.githubusercontent.com/ohmyzsh/ohmyzsh/master/tools/install.sh)" "" --unattended
+if ! omz_installer=$(curl -fsSL https://raw.githubusercontent.com/ohmyzsh/ohmyzsh/master/tools/install.sh); then
+  echo "error: could not download the oh-my-zsh installer" >&2
+  exit 1
+fi
+CHSH=no sh -c "$omz_installer" "" --unattended
 
 # Print commands
 set -x
 
 # Install Oh-My-Zsh plugins
-git clone https://github.com/zsh-users/zsh-history-substring-search.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-history-substring-search
-git clone https://github.com/zsh-users/zsh-autosuggestions.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-autosuggestions
-git clone https://github.com/z-shell/zsh-eza.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-eza
-git clone --depth 1 https://github.com/unixorn/fzf-zsh-plugin.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/fzf-zsh-plugin
-git clone https://github.com/zsh-users/zsh-syntax-highlighting.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-syntax-highlighting
-git clone --depth 1 https://github.com/marlonrichert/zsh-autocomplete.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-autocomplete
+# Note: use $HOME, not ~ inside ${VAR:-...} — tilde is not expanded there,
+# which would clone into a literal ./~ directory.
+ZSH_CUSTOM_DIR="${ZSH_CUSTOM:-$HOME/.oh-my-zsh/custom}"
+clone_plugin() {
+  local dest="$1"
+  shift
+  if ! git clone "$@" "$dest"; then
+    echo "warning: failed to clone into $dest (skipping)" >&2
+  fi
+}
+clone_plugin "$ZSH_CUSTOM_DIR/plugins/zsh-history-substring-search" https://github.com/zsh-users/zsh-history-substring-search.git
+clone_plugin "$ZSH_CUSTOM_DIR/plugins/zsh-autosuggestions" https://github.com/zsh-users/zsh-autosuggestions.git
+clone_plugin "$ZSH_CUSTOM_DIR/plugins/zsh-eza" https://github.com/z-shell/zsh-eza.git
+clone_plugin "$ZSH_CUSTOM_DIR/plugins/fzf-zsh-plugin" --depth=1 https://github.com/unixorn/fzf-zsh-plugin.git
+clone_plugin "$ZSH_CUSTOM_DIR/plugins/zsh-syntax-highlighting" https://github.com/zsh-users/zsh-syntax-highlighting.git
+clone_plugin "$ZSH_CUSTOM_DIR/plugins/zsh-autocomplete" --depth=1 https://github.com/marlonrichert/zsh-autocomplete.git
 
 
-# Disable exit on error
-set +eu
-
-# Backup old config file if it exists
-cp ~/.zshrc ~/.zshrc{,.bak} -r
-
-# Enable exit on error
-set -eu
-
 # Download and replace config file
 curl -fsSL https://raw.githubusercontent.com/alvinlollo/Single-install-script/refs/heads/main/configs/.zshrc -o ~/.zshrc
 
@@ -108,33 +130,47 @@ touch ~/.fzf/shell/key-bindings.zsh
 set +x
 
 # If this user's login shell is already "zsh", do not attempt to switch.
-if [ "$(basename -- "$SHELL")" = "zsh" ]; then
+user_name="${USER:-${LOGNAME:-$(id -un)}}"
+if command -v getent >/dev/null 2>&1; then
+  login_shell="$(getent passwd "$user_name" | awk -F: '{print $7}' | tr -d '\n')"
+else
+  login_shell="$(grep -E "^${user_name}:" /etc/passwd | awk -F: '{print $7}' | tr -d '\n' || true)"
+fi
+
+if [ -z "${login_shell:-}" ]; then
+  login_shell="${SHELL:-}"
+fi
+
+if [ "$(basename -- "${login_shell:-}")" = "zsh" ]; then
   echo "You already have zsh as the default shell"
   echo "Successfully installed zsh configuration"
   exit 0 # Exit as success
 fi
 
-if command -v chsh >/dev/null; then
+if ! command -v chsh >/dev/null; then
   echo "chsh command does not exist."
-  echo "Please change your shell manually"
-  sleep 5 && exit 0
+  echo "Please change your shell manually:"
+  echo "chsh -s \"$zsh\""
+  echo "Successfully installed zsh configuration"
+  exit 0
 fi
 
 echo "Changing your shell to $zsh..."
 
-if ! echo "+ sudo -k chsh -s "$zsh" "$USER"" && sudo -k chsh -s "$zsh" "$USER"; then # -k forces password prompt
-  echo "Next command may fail."
-  echo "+ chsh -s \"$(which zsh)\" \"$USER\""
-  chsh -s "$(which zsh)" "$USER"  # run chsh normally may fail
-fi
-
-# Check if the shell change was successful
-if [ $? -ne 0 ]; then
-  echo "chsh command unsuccessful. Change your default shell manually:"
-  echo "chsh -s \"$(which zsh)\" \"$USER\""
-else
+echo "+ sudo -k chsh -s \"$zsh\" \"$user_name\""
+if sudo -k chsh -s "$zsh" "$user_name"; then # -k forces password prompt
   export SHELL="$zsh"
   echo "Shell successfully changed to '$zsh'."
+else
+  echo "sudo chsh failed. Trying without sudo (this may fail):"
+  echo "+ chsh -s \"$zsh\" \"$user_name\""
+  if chsh -s "$zsh" "$user_name"; then
+    export SHELL="$zsh"
+    echo "Shell successfully changed to '$zsh'."
+  else
+    echo "chsh command unsuccessful. Change your default shell manually:"
+    echo "chsh -s \"$zsh\" \"$user_name\""
+  fi
 fi
 
 echo "Successfully installed zsh"