Degrade gracefully (no checksumming or mirrors) if MD5 is unavailable

bin/ruby-build

@@ -138,12 +138,15 @@ compute_md5() {
     local output="$(md5sum -b)"
     echo "${output% *}"
   else
-    echo "error: please install \`md5sum\` and try again" >&2
-    exit 1
+    return 1
   fi
 }
 
 verify_checksum() {
+  if [ -z "$HAS_MD5_SUPPORT" ]; then
+    return 0
+  fi
+
   local filename="$1"
   if [ ! -e "$filename" ]; then
     return 1
@@ -591,6 +594,13 @@ if [ -n "$RUBY_BUILD_SKIP_MIRROR" ]; then
   unset RUBY_BUILD_MIRROR_URL
 fi
 
+if echo test | compute_md5 >/dev/null; then
+  HAS_MD5_SUPPORT=1
+else
+  unset HAS_MD5_SUPPORT
+  unset RUBY_BUILD_MIRROR_URL
+fi
+
 SEED="$(date "+%Y%m%d%H%M%S").$$"
 LOG_PATH="${TMP}/ruby-build.${SEED}.log"
 RUBY_BIN="${PREFIX_PATH}/bin/ruby"