Script to install zsh on Windows, without WSL

install-zsh.sh

#!/bin/bash

# This script installs or updates Zsh on Windows using Git Bash.
# It requires elevated privileges and the following commands:
#   - git
# If Git is not installed, the script will stop.
# The script will:
# 1. Check if it is running with elevated privileges on Windows and stop if it is not.
# 2. Check if Git is installed and stop if it is not.
# 3. Automatically determine the latest version of zstd, download, and install it if it is not available and Zsh needs to be installed or updated.
# 4. Emit help text with usage and requirements if any checks fail.
# 5. Avoid duplicate entries in .bashrc for setting Zsh as the default shell.
# 6. Only install Oh My Zsh if it is not already installed.
# 7. Proceed with the Zsh installation and update process if all checks pass.

# Function to display help text
display_help() {
    echo "Usage: ./install_zsh.sh"
    echo ""
    echo "This script installs or updates Zsh on Windows using Git Bash."
    echo "It requires elevated privileges and the following commands:"
    echo "  - git"
    echo ""
    echo "Steps to run the script:"
    echo "1. Open Git Bash as an administrator."
    echo "2. Navigate to the directory where you saved the script."
    echo "3. Make the script executable: chmod +x install_zsh.sh"
    echo "4. Run the script: ./install_zsh.sh"
    exit 1
}

# Function to check if the script is running with elevated privileges on Windows
check_admin() {
    if [[ "$OSTYPE" == "msys" || "$OSTYPE" == "cygwin" ]]; then
        net session > /dev/null 2>&1
        if [[ $? -ne 0 ]]; then
            echo "This script must be run as an administrator."
            display_help
        fi
    fi
}

# Function to check if Git is installed
check_git_installed() {
    if ! command -v git &> /dev/null; then
        echo "Git is not installed or not in the PATH."
        display_help
    fi
}

# Function to download and install the latest zstd if not available
install_zstd() {
    if ! command -v zstd &> /dev/null; then
        echo "zstd is not installed. Downloading and installing the latest zstd..."
        LATEST_ZSTD_URL=$(curl -s https://api.github.com/repos/facebook/zstd/releases/latest | grep "browser_download_url.*win64.zip" | cut -d '"' -f 4)
        curl -L -o zstd.zip $LATEST_ZSTD_URL
        unzip zstd.zip -d zstd
        cp zstd/zstd.exe "$GIT_INSTALL_DIR/usr/bin/"
        rm -rf zstd zstd.zip
    fi
}

# Check for elevated privileges
check_admin

# Check if Git is installed
check_git_installed

# Define variables
ZSH_PAGE_URL="https://packages.msys2.org/package/zsh?repo=msys&variant=x86_64"
GIT_INSTALL_DIR=$(find_git_install_dir)

# Download the Zsh package page
echo "Downloading Zsh package page..."
curl -L -o zsh_page.html $ZSH_PAGE_URL

# Extract the latest Zsh version from the page
LATEST_ZSH_VERSION=$(grep -oP 'zsh-\K[0-9]+\.[0-9]+\.[0-9]+' zsh_page.html | head -n 1)
INSTALLED_ZSH_VERSION=$(get_installed_zsh_version)

echo "Installed Zsh version: $INSTALLED_ZSH_VERSION"
echo "Latest Zsh version: $LATEST_ZSH_VERSION"

# Compare versions and download if necessary
if version_greater "$LATEST_ZSH_VERSION" "$INSTALLED_ZSH_VERSION"; then
    echo "Updating Zsh to version $LATEST_ZSH_VERSION..."

    # Ensure zstd is installed
    install_zstd

    ZSH_DOWNLOAD_URL=$(grep -oP 'https://mirror.msys2.org/msys/x86_64/zsh-[^"]+\.pkg\.tar\.zst' zsh_page.html | head -n 1)
    curl -L -o zsh.pkg.tar.zst $ZSH_DOWNLOAD_URL

    # Extract Zsh package using tar
    echo "Extracting Zsh package..."
    tar -I zstd -xvf zsh.pkg.tar.zst -C "$GIT_INSTALL_DIR"

    # Clean up
    echo "Cleaning up..."
    rm zsh.pkg.tar.zst
else
    echo "Zsh is already up to date."
fi

# Clean up the downloaded page
rm zsh_page.html

# Set Zsh as the default shell if not already set
if ! grep -q 'exec zsh' ~/.bashrc; then
    echo "Setting Zsh as the default shell..."
    echo 'if [ -t 1 ]; then exec zsh; fi' >> ~/.bashrc
else
    echo "Zsh is already set as the default shell in .bashrc."
fi

# Install Oh My Zsh (optional)
if [ ! -d "$HOME/.oh-my-zsh" ]; then
    echo "Installing Oh My Zsh..."
    sh -c "$(curl -fsSL https://raw.githubusercontent.com/ohmyzsh/ohmyzsh/master/tools/install.sh)"
else
    echo "Oh My Zsh is already installed."
fi

echo "Zsh installation completed!"