Several changes:

- Small fixes to output syntax.
- Verifies a user has permissions to install packages, before attempting
to install them.
- Checks if a package is installed, before attempting to install it.

run_onchange_install-packages.bash.tmpl

@@ -9,14 +9,34 @@
 ## Used to colorize output.
 C_GREEN="$(printf '\033[0;32m')"
 C_BLUE="$(printf '\033[0;34m')"
+C_CYAN="$(printf '\033[0;36m')"
 C_RED="$(printf '\033[1;31m')"
 C_NC="$(printf '\033[0m')"
-readonly C_GREEN C_BLUE C_RED C_NC
+readonly C_GREEN C_BLUE C_CYAN C_RED C_NC
 
 ## Short-hand colorized messages.
 readonly C_SUCCESS="${C_GREEN}==>${C_NC} "
 readonly C_ERROR="${C_RED}ERROR:${C_NC} "
 readonly C_INFO="${C_BLUE}==>${C_NC} "
+readonly C_NOTE="${C_CYAN}==>${C_NC} "
+
+
+####[ Prepping ]########################################################################
+
+
+# Permissions only need to be checked on Linux, as Homebrew on macOS doesn't require
+# elevated permissions.
+if [[ {{ .chezmoi.os }} == "linux" ]]; then
+    echo "${C_INFO}Checking user permissions..."
+    echo "${C_INFO}    Executing: 'sudo -l'"
+    if sudo -l &> /dev/null; then
+        echo "${C_SUCCESS}'${USER}' has permissions to install packages"
+    else
+        echo "${C_ERROR}'${USER}' does not have permissions to install packages"
+        echo "${C_INFO}Skipping package installation"
+        exit 1
+    fi
+fi
 
 
 ####[ Main ]############################################################################
@@ -31,32 +51,53 @@ case "{{ .chezmoi.os }}" in
     if hash pacman &> /dev/null; then
         sudo pacman -Syu --noconfirm
         {{- range .packages.linux.general }}
-        echo "${C_INFO}Installing {{ . }}..."
-        sudo pacman -S --noconfirm --needed "{{ . }}"
+        if pacman -Q "{{ . }}" &> /dev/null; then
+            echo "${C_NOTE}'{{ . }}' is already installed"
+            echo "${C_INFO}Skipping..."
+        else
+            echo "${C_INFO}Installing '{{ . }}'..."
+            sudo pacman -S --noconfirm --needed "{{ . }}"
+        fi
         {{- end }}
     elif hash apt &> /dev/null; then
         sudo apt update
         {{- range .packages.linux.general }}
-        echo "${C_INFO}Installing {{ . }}..."
-        sudo apt install -y "{{ . }}"
+        if dpkg -l "{{ . }}" &> /dev/null; then
+            echo "${C_NOTE}'{{ . }}' is already installed"
+            echo "${C_INFO}Skipping..."
+        else
+            echo "${C_INFO}Installing '{{ . }}'..."
+            sudo apt install -y "{{ . }}"
+        fi
         {{- end }}
     fi
 
     # Install Pacman-specific packages
     if hash pacman &> /dev/null; then
         echo "${C_INFO}Installing pacman-specific packages..."
         {{- range .packages.linux.pacman }}
-        echo "${C_INFO}Installing {{ . }}..."
-        sudo pacman -S --noconfirm --needed "{{ . }}"
+        if pacman -Q "{{ . }}" &> /dev/null; then
+            echo "${C_NOTE}'{{ . }}' is already installed"
+            echo "${C_INFO}Skipping..."
+        else
+            echo "${C_INFO}Installing '{{ . }}'..."
+            sudo pacman -S --noconfirm --needed "{{ . }}"
+        fi
         {{- end }}
     fi
 
     # Install APT-specific packages
     if hash apt &> /dev/null; then
         echo "${C_INFO}Installing apt-specific packages..."
         {{- range .packages.linux.apt }}
-        echo "${C_INFO}Installing {{ . }}..."
-        sudo apt install -y "{{ . }}"
+        if dpkg -l "{{ . }}" &> /dev/null; then
+            echo "${C_NOTE}'{{ . }}' is already installed"
+            echo "${C_INFO}Skipping..."
+            continue
+        else
+            echo "${C_INFO}Installing '{{ . }}'..."
+            sudo apt install -y "{{ . }}"
+        fi
         {{- end }}
     fi
     ;;
@@ -67,8 +108,13 @@ case "{{ .chezmoi.os }}" in
     # Install Homebrew packages
     echo "${C_INFO}Installing Homebrew formulas..."
     {{- range .packages.macos.homebrew.formulas }}
-    echo "${C_INFO}Installing {{ . }}..."
-    brew install "{{ . }}"
+    if brew list -1 | grep "{{ . }}" &> /dev/null; then
+        echo "${C_NOTE}'{{ . }}' is already installed"
+        echo "${C_INFO}Skipping..."
+    else
+        echo "${C_INFO}Installing '{{ . }}'..."
+        brew install "{{ . }}"
+    fi
     {{- end }}
     ;;
 
@@ -78,5 +124,5 @@ case "{{ .chezmoi.os }}" in
     ;;
 esac
 
-echo "${C_GREEN}Package installation complete"
+echo "${C_SUCCESS}Package installation complete"