installer: reorganise and add comments

tools/install.sh

 #!/bin/sh
+#
+# This script should be run via curl:
+#   sh -c "$(curl -fsSL https://raw.githubusercontent.com/robbyrussell/oh-my-zsh/master/tools/install.sh)"
+# or wget:
+#   sh -c "$(wget -qO- https://raw.githubusercontent.com/robbyrussell/oh-my-zsh/master/tools/install.sh)"
+#
+# As an alternative, you can download the install script separately and
+# run it afterwards with `sh install.sh'
+#
 set -e
 
-# Test command existence (POSIX compatible)
+# Default location
+ZSH=${ZSH:-~/.oh-my-zsh}
+
 command_exists() {
 	command -v "$@" >/dev/null 2>&1
 }
@@ -30,17 +41,15 @@ main() {
 	fi
 
 	if ! command_exists zsh; then
-		printf "${YELLOW}Zsh is not installed!${NORMAL} Please install zsh first!\n"
+		echo "${YELLOW}Zsh is not installed!${NORMAL} Please install zsh first!"
 		exit 1
 	fi
 
-	if [ ! -n "$ZSH" ]; then
-		ZSH=~/.oh-my-zsh
-	fi
-
 	if [ -d "$ZSH" ]; then
-		printf "${YELLOW}You already have Oh My Zsh installed.${NORMAL}\n"
-		printf "You'll need to remove $ZSH if you want to re-install.\n"
+		cat <<-EOF
+			${YELLOW}You already have Oh My Zsh installed.${NORMAL}
+			You'll need to remove $ZSH if you want to re-install.
+		EOF
 		exit 1
 	fi
 
@@ -51,31 +60,34 @@ main() {
 	# precedence over umasks except for filesystems mounted with option "noacl".
 	umask g-w,o-w
 
-	printf "${BLUE}Cloning Oh My Zsh...${NORMAL}\n"
+	echo "${BLUE}Cloning Oh My Zsh...${NORMAL}"
+
 	command_exists git || {
 		echo "Error: git is not installed"
 		exit 1
 	}
-	# The Windows (MSYS) Git is not compatible with normal use on cygwin
-	if [ "$OSTYPE" = cygwin ]; then
-		if git --version | grep msysgit > /dev/null; then
-			echo "Error: Windows/MSYS Git is not supported on Cygwin"
-			echo "Error: Make sure the Cygwin git package is installed and is first on the path"
+
+	if [ "$OSTYPE" = cygwin ] && git --version | grep -q msysgit; then
+		cat <<-EOF
+			Error: Windows/MSYS Git is not supported on Cygwin
+			Error: Make sure the Cygwin git package is installed and is first on the $PATH
+		EOF
 		exit 1
 	fi
-	fi
-	env git clone --depth=1 https://github.com/robbyrussell/oh-my-zsh.git "$ZSH" || {
-		printf "Error: git clone of oh-my-zsh repo failed\n"
+
+	git clone --depth=1 https://github.com/robbyrussell/oh-my-zsh.git "$ZSH" || {
+		echo "Error: git clone of oh-my-zsh repo failed"
 		exit 1
 	}
 
-	printf "${BLUE}Looking for an existing zsh config...${NORMAL}\n"
+	echo "${BLUE}Looking for an existing zsh config...${NORMAL}"
 	if [ -f ~/.zshrc ] || [ -h ~/.zshrc ]; then
-		printf "${YELLOW}Found ~/.zshrc.${NORMAL} ${GREEN}Backing up to ~/.zshrc.pre-oh-my-zsh${NORMAL}\n";
+		echo "${YELLOW}Found ~/.zshrc.${GREEN} Backing up to ~/.zshrc.pre-oh-my-zsh.${NORMAL}"
 		mv ~/.zshrc ~/.zshrc.pre-oh-my-zsh;
 	fi
 
-	printf "${BLUE}Using the Oh My Zsh template file and adding it to ~/.zshrc${NORMAL}\n"
+	echo "${BLUE}Using the Oh My Zsh template file and adding it to ~/.zshrc.${NORMAL}"
+
 	cp "$ZSH/templates/zshrc.zsh-template" ~/.zshrc
 	sed "/^export ZSH=/ c\\
 export ZSH=\"$ZSH\"
@@ -87,31 +99,36 @@ export ZSH=\"$ZSH\"
 	if [ "$TEST_CURRENT_SHELL" != "zsh" ]; then
 		# If this platform provides a "chsh" command (not Cygwin), do it, man!
 		if command_exists chsh; then
-			printf "${BLUE}Time to change your default shell to zsh!${NORMAL}\n"
+			echo "${BLUE}Time to change your default shell to zsh!${NORMAL}"
 			chsh -s $(grep /zsh$ /etc/shells | tail -1)
 		# Else, suggest the user do so manually.
 		else
-			printf "I can't change your shell automatically because this system does not have chsh.\n"
-			printf "${BLUE}Please manually change your default shell to zsh!${NORMAL}\n"
+			cat <<-EOF
+				I can't change your shell automatically because this system does not have chsh.
+				${BLUE}Please manually change your default shell to zsh${NORMAL}
+			EOF
 		fi
 	fi
 
-	printf "${GREEN}"
-	echo '         __                                     __   '
-	echo '  ____  / /_     ____ ___  __  __   ____  _____/ /_  '
-	echo ' / __ \/ __ \   / __ `__ \/ / / /  /_  / / ___/ __ \ '
-	echo '/ /_/ / / / /  / / / / / / /_/ /    / /_(__  ) / / / '
-	echo '\____/_/ /_/  /_/ /_/ /_/\__, /    /___/____/_/ /_/  '
-	echo '                        /____/                       ....is now installed!'
-	echo ''
-	echo ''
-	echo 'Please look over the ~/.zshrc file to select plugins, themes, and options.'
-	echo ''
-	echo 'p.s. Follow us at https://twitter.com/ohmyzsh'
-	echo ''
-	echo 'p.p.s. Get stickers, shirts, and coffee mugs at https://shop.planetargon.com/collections/oh-my-zsh'
-	echo ''
-	printf "${NORMAL}"
+	printf "$GREEN"
+	cat <<-'EOF'
+		         __                                     __
+		  ____  / /_     ____ ___  __  __   ____  _____/ /_
+		 / __ \/ __ \   / __ `__ \/ / / /  /_  / / ___/ __ \
+		/ /_/ / / / /  / / / / / / /_/ /    / /_(__  ) / / /
+		\____/_/ /_/  /_/ /_/ /_/\__, /    /___/____/_/ /_/
+		                        /____/                       ....is now installed!
+
+
+		Please look over the ~/.zshrc file to select plugins, themes, and options.
+
+		p.s. Follow us on https://twitter.com/ohmyzsh
+
+		p.p.s. Get stickers, shirts, and coffee mugs at https://shop.planetargon.com/collections/oh-my-zsh
+
+	EOF
+	printf "$NORMAL"
+
 	env zsh -l
 }