Improve visibility of GNU awk dependency

README.md

@@ -29,6 +29,8 @@ Goals of this project:
 # Requirements
 
 - Mac OS X or Linux.
+- GNU awk.  Not installed by default on Mac but available via Homebrew.  `brew
+  install gawk`
 - More than two CPU cores recommended.
 - More than 6GB of RAM recommended if running Jenkins.
 

scripts/upgrade/remote_dependencies.sh

@@ -7,6 +7,13 @@ if [ -z "${JENKINS_WEB}" -o -z "${SCRIPT_LIBRARY_PATH}" ]; then
   exit 1
 fi
 
+if ! type -P gawk; then
+  echo 'ERROR: GNU awk is required.' >&2
+  echo 'If on Mac, "brew install gawk".' >&2
+  echo "Otherwise, install GNU awk for the platform you're using" >&2
+  exit 1
+fi
+
 # GNU or BSD sed is required.  Homebrew on Mac installs GNU sed as gsed.
 # Try to detect gsed; otherwise, fall back to detecting OS for using sed.
 SED=()