Prompt the user before performing particularly expensive operations....

build/install-build-deps.sh

 #!/bin/bash -e
 
 # Script to install everything needed to build chromium (well, ideally, anyway)
 # See http://code.google.com/p/chromium/wiki/LinuxBuildInstructions
 # and http://code.google.com/p/chromium/wiki/LinuxBuild64Bit
 
 if ! egrep -q "Ubuntu 8.04|Ubuntu 8.10" /etc/issue; then
   echo "Only Ubuntu 8.04 and 8.10 are currently supported" >&2
   exit 1
 fi
 
 if ! uname -m | egrep -q "i686|x86_64"; then
   echo "Only x86 architectures are currently supported" >&2
   exit
 fi
 
 if [ "x$(id -u)" != x0 ]; then
   echo "Running as non-root user."
   echo "You might have to enter your password one or more times for 'sudo'."
+  echo
 fi
 
 # Packages need for development
 dev_list="subversion pkg-config python perl g++ g++-multilib bison flex gperf
           libnss3-dev libglib2.0-dev libgtk2.0-dev libnspr4-dev libsqlite3-dev
           wdiff lighttpd php5-cgi msttcorefonts sun-java6-fonts"
 
 # Full list of required run-time libraries
 lib_list="libatk1.0-0 libc6 libcairo2 libexpat1 libfontconfig1 libfreetype6
           libglib2.0-0 libgtk2.0-0 libnspr4-0d libnss3-1d libpango1.0-0
           libpcre3 libpixman-1-0 libpng12-0 libstdc++6 libsqlite3-0 libx11-6
           libxau6 libxcb-xlib0 libxcb1 libxcomposite1 libxcursor1 libxdamage1
           libxdmcp6 libxext6 libxfixes3 libxi6 libxinerama1 libxrandr2
           libxrender1 zlib1g"
 
 # Debugging symbols for all of the run-time libraries
 dbg_list="libatk1.0-dbg libc6-dbg libcairo2-dbg libfontconfig1-dbg
           libglib2.0-0-dbg libgtk2.0-0-dbg libnspr4-0d-dbg libnss3-1d-dbg
           libpango1.0-0-dbg libpcre3-dbg libpixman-1-0-dbg libx11-6-dbg
           libxau6-dbg libxcb-xlib0-dbg libxcb1-dbg libxcomposite1-dbg
           libxcursor1-dbg libxdamage1-dbg libxdmcp6-dbg libxext6-dbg
           libxfixes3-dbg libxi6-dbg libxinerama1-dbg libxrandr2-dbg
           libxrender1-dbg zlib1g-dbg"
 
 # Standard 32bit compatibility libraries
 cmp_list="ia32-libs lib32stdc++6 lib32z1 lib32z1-dev libc6-dev-i386 libc6-i386"
 
-echo "Updating list of available packages..."
+# Waits for the user to press 'Y' or 'N'. Either uppercase of lowercase is
+# accepted. Returns 0 for 'Y' and 1 for 'N'. If an optional parameter has
+# been provided to yes_no(), the function also accepts RETURN as a user input.
+# The parameter specifies the exit code that should be returned in that case.
+# The function will echo the user's selection followed by a newline character.
+# Users can abort the function by pressing CTRL-C. This will call "exit 1".
+yes_no() {
+  local c
+  while :; do
+    c="$(trap 'stty echo -iuclc icanon 2>/dev/null' EXIT INT TERM QUIT
+         stty -echo iuclc -icanon 2>/dev/null
+         dd count=1 bs=1 2>/dev/null | od -An -tx1)"
+    case "$c" in
+      " 0a") if [ -n "$1" ]; then
+               [ $1 -eq 0 ] && echo "Y" || echo "N"
+               return $1
+             fi
+             ;;
+      " 79") echo "Y"
+             return 0
+             ;;
+      " 6e") echo "N"
+             return 1
+             ;;
+      "")    echo "Aborted" >&2
+             exit 1
+             ;;
+      *)     # The user pressed an unrecognized key. As we are not echoing
+             # any incorrect user input, alert the user by ringing the bell.
+             (tput bel) 2>/dev/null
+             ;;
+    esac
+  done
+}
+
+echo "This script installs all required libraries for building Chromium."
+echo "For most of the libraries, it can also install debugging symbols, which"
+echo "will allow you to debug code in the system libraries. Most developers"
+echo "won't need these symbols."
+echo -n "Do you want me to install them for you (y/N) "
+if yes_no 1; then
+  echo "Installing debugging symbols."
+else
+  echo "Skipping installation of debugging symbols."
+  dbg_list=
+fi
+
 sudo apt-get update
 
 # We initially run "apt-get" with the --reinstall option and parse its output.
 # This way, we can find all the packages that need to be newly installed
 # without accidentally promoting any packages from "auto" to "manual".
 # We then re-run "apt-get" with just the list of missing packages.
 echo "Finding missing packages..."
 new_list="$(yes n |
             sudo apt-get install --reinstall \
                          ${pkg_list} ${lib_list} ${dbg_list} \
                          $([ "$(uname -m)" = x86_64 ] && echo ${cmp_list}) \
                          2>/dev/null |
             sed -e 's/^  //;t;d')"
 
 echo "Installing missing packages..."
 sudo apt-get install ${new_list}
 
 # Install 32bit backwards compatibility support for 64bit systems
 if [ "$(uname -m)" = x86_64 ]; then
   echo "Installing 32bit libraries that are not already provided by the system"
+  echo
+  echo "While we only need to install a relatively small number of library"
+  echo "files, we temporarily need to download a lot of large *.deb packages"
+  echo "that contain these files. We will create new *.deb packages that"
+  echo "include just the 32bit libraries. These files will then be found on"
+  echo "your system in places like /lib32, /usr/lib32, /usr/lib/debug/lib32,"
+  echo "/usr/lib/debug/usr/lib32. If you ever need to uninstall these files,"
+  echo "look for packages named *-ia32.deb."
+  echo "Do you want me to download all packages needed to build new 32bit"
+  echo -n "package files (Y/n) "
+  if ! yes_no 0; then
+    echo "Exiting without installing any 32bit libraries."
+    exit 0
+  fi
   tmp=/tmp/install-32bit.$$
   trap 'rm -rf "${tmp}"' EXIT INT TERM QUIT
   mkdir -p "${tmp}/apt/lists/partial" "${tmp}/cache" "${tmp}/partial"
   touch "${tmp}/status"
 
   [ -r /etc/apt/apt.conf ] && cp /etc/apt/apt.conf "${tmp}/apt/"
   cat >>"${tmp}/apt/apt.conf" <<-EOF
         Apt::Architecture "i386";
         Dir::Cache "${tmp}/cache";
         Dir::Cache::Archives "${tmp}/";
@@ skipping 98 matching lines @@
              sed -e 's/[.]so[.][0-9].*/.so/' |
              sort -u); do
     [ "x${i##*/}" = "xld-linux.so" ] && continue
     [ -r "$i" ] && continue
     j="$(ls "$i."* | sed -e 's/.*[.]so[.]\([^.]*\)$/\1/;t;d' |
          sort -n | tail -n 1)"
     [ -r "$i.$j" ] || continue
     sudo ln -s "${i##*/}.$j" "$i"
   done
 fi