Create get-ghcup.sh, fixes #36

This follows the style of the rustup installation script that has a friendly welcome message, tells you what the script is going to do, and then asks if you'd like to proceed. This is meant to be a one-command setup of everything you need to get started with Haskell.

I already had this written so adding it for comparison to #40. Would still need to update README and clean a few things up. Let me know what you think!

get-ghcup.sh

+#!/bin/sh -e
+#
+# ghcup installation script.
+#
+# This installs 'ghcup', 'cabal', and 'ghc'.
+
+    ##########################
+    #--[ Global Variables ]--#
+    ##########################
+
+# @VARIABLE: GHCUP
+# @DESCRIPTION:
+# The name of the ghcup executable.
+GHCUP="ghcup"
+
+# @VARIABLE: INSTALL_BASE
+# @DESCRIPTION:
+# The main install directory where all ghcup stuff happens.
+INSTALL_BASE="$HOME/.ghcup"
+
+# @VARIABLE: BIN_LOCATION
+# @DESCRIPTION:
+# The location where ghcup will create symlinks for GHC binaries.
+# This is expected to be a subdirectory of INSTALL_BASE.
+BIN_LOCATION="$INSTALL_BASE/bin"
+
+# @VARIABLE: GHCUP
+# @DESCRIPTION:
+# The name of the ghcup executable.
+GHCUP_EXE="$BIN_LOCATION/$GHCUP"
+
+
+    ##########################
+    #--[ Helper Functions ]--#
+    ##########################
+
+
+# @FUNCTION: command_exists
+# @USAGE: <command>
+# @DESCRIPTION:
+# Check if a command exists (no arguments).
+# @RETURNS: 0 if the command exists, non-zero otherwise
+command_exists() {
+    [ -z "$1" ] && die "Internal error: no argument given to command_exists"
+
+    command -V "$1" >/dev/null 2>&1
+    return $?
+}
+
+# @FUNCTION: die
+# @USAGE: [msg]
+# @DESCRIPTION:
+# Exits the shell script with status code 2
+# and prints the given message in red to STDERR, if any.
+die() {
+    (>&2 printf "\\033[0;31m%s\\033[0m\\n" "$1")
+    exit 2
+}
+
+# @FUNCTION: has_ghcup
+# @USAGE: <no args>
+# @DESCRIPTION:
+# Checks to see if the ghcup executable exists.
+has_ghcup() {
+  command_exists "${GHCUP_EXE}"
+}
+
+# @FUNCTION: on_path
+# @USAGE: <path-piece>
+# @DESCRIPTION:
+# Checks to see if the <path-piece> is in the PATH environment variable.
+on_path() {
+  echo ":$PATH:" | grep -q :"$1":
+}
+
+# @FUNCTION: on_path
+# @USAGE: <no args>
+# @DESCRIPTION:
+# Checks to see if the ghcup bin directory is in the PATH environment variable.
+ghcup_on_path() {
+  on_path "${BIN_LOCATION}"
+}
+
+
+    ############################
+    #--[ Installation Logic ]--#
+    ############################
+
+
+# @FUNCTION: preamble
+# @USAGE: <no args>
+# @DESCRIPTION:
+# Prints a welcome message to the terminal and informs the user what the script
+# is going to do. They can cancel by pressing ctrl-c.
+preamble () {
+  echo
+  echo "Welcome to Haskell!"
+  echo
+  echo "This will download and install the Glasgow Haskell Compiler (GHC) for "
+  echo "the Haskell programming language, and the Cabal build tool."
+  echo
+  echo "It will add the 'cabal', 'ghc', and 'ghcup' executables to bin directory "
+  echo "located at: "
+  echo
+  echo "  ${BIN_LOCATION}"
+  echo
+  echo "This path will then be added to your PATH environment variable by "
+  echo "modifying the bashrc file at:"
+  echo
+  echo "  $HOME/.bashrc"
+  echo
+  echo "To proceed with the installation press enter, to cancel press ctrl-c"
+  echo
+
+  # Wait for user input to continue.
+  read
+}
+
+# @FUNCTION: check_for_ghcup_installation
+# @USAGE: <no args>
+# @DESCRIPTION:
+# Check if the 'ghcup' command already exists, if so provide instructions
+# for upgrading.
+check_for_ghcup_installation() {
+  if has_ghcup; then
+    echo
+    echo "Welcome to Haskell!"
+    echo
+    echo  "We noticed that you already have 'ghcup' installed:"
+    echo
+    echo "  Location: ${GHCUP_EXE}"
+    echo "  Version: `${GHCUP_EXE} --version`"
+    echo
+    echo "To upgrade to the latest version of ghcup run:"
+    echo
+    echo "  ghcup self-update"
+    echo
+    echo "To upgrade to the newest ghc and cabal versions run:"
+    echo
+    echo "  ghcup install && ghcup install-cabal"
+    echo
+
+    if ! ghcup_on_path; then
+      echo
+      echo "We noticed you don't have ghcup's bin directory ($HOME/.ghcup/bin)"
+      echo "in your PATH environment variable. To configure your current shell: "
+      echo
+      echo "  source $HOME/.ghcup/env"
+      echo
+    fi
+
+    exit 0
+  fi
+}
+
+# @FUNCTION: source_ghcup_env_from_bashrc
+# @USAGE: <no args>
+# @DESCRIPTION:
+# Check to see if the ghcup env file is sourced from .bashrc, if not add it.
+source_ghcup_env_from_bashrc () {
+  # Check to see if the .bashrc file sources the ghcup environement file, if
+  # not then add it.
+  if [ -z "`cat "$HOME/.bashrc" | grep 'source "$HOME/.ghcup/env"'`" ]; then
+    echo "Updating $HOME/.bashrc to source ghcup environment file..."
+    echo 'source "$HOME/.ghcup/env"' >> $HOME/.bashrc
+   fi
+}
+
+# @FUNCTION: install_ghcup
+# @USAGE: <no args>
+# @DESCRIPTION:
+# Install ghcup, ghc, and cabal.
+install_ghcup () {
+  preamble
+  
+  echo "Creating ghcup directories..."
+  mkdir -p "${BIN_LOCATION}"
+  echo "  Done. Created ${BIN_LOCATION}"
+  echo
+  echo "Downloading ghcup..."
+  curl https://raw.githubusercontent.com/haskell/ghcup/master/ghcup > ${GHCUP_EXE} && chmod +x ${GHCUP_EXE}
+  echo "  Done. Installed at ${GHCUP_EXE}"
+  echo
+
+  # Install ghc and cabal.
+  ${GHCUP_EXE} install
+
+  echo
+  echo "Installing the cabal build tool..."
+  ${GHCUP_EXE} install-cabal
+
+  # Create env file.
+  echo 'export PATH="$HOME/.cabal/bin:$HOME/.ghcup/bin:$PATH"' > $INSTALL_BASE/env
+
+  echo
+  echo "The Haskell toolchain is now installed!"
+  echo
+}
+
+# @FUNCTION: check_for_ghcup_bin_on_path
+# @USAGE: <no args>
+# @DESCRIPTION:
+# Check to see if the ghcup bin directory is on the PATH, if no provide
+# instructions for how to add it.
+check_for_ghcup_bin_on_path() {
+  if ! ghcup_on_path; then
+    echo
+    echo "To get started you need ghcup's bin directory ($HOME/.ghcup/bin)"
+    echo "in your PATH environment variable. To configure your current shell: "
+    echo
+    echo "  source $HOME/.ghcup/env"
+    echo
+  fi
+}
+
+
+# --------------------------------------------------
+#  Main
+# --------------------------------------------------
+
+main () {
+  check_for_ghcup_installation
+  install_ghcup
+  source_ghcup_env_from_bashrc
+  check_for_ghcup_bin_on_path
+}
+
+main

[Ghost User]

Uh, no, never :)

Changing user configuration files like bashrc is something that I don't want to do at all. This is very intrusive and may not even work, depending on how the bashrc file is structured.

[Matt Renaud]

Yeah I wasn't sold on this either, the rustup script does something similar, but adds it to .profile which is arguably the correct place. I used .bashrc to mirror the readme instructions but you're correct this could very well break things. It would be nice if system configuration was a bit more structured :)

[Ghost User]

I think it would be ok if this is interactive and asks in CAPITAL LETTERS IF YOU REALLY WANT US TO APPEND TO YOUR BASHRC ;)