Trap failures and print an error message. Use file descriptors to avoid swallowing errors.

bin/ruby-build

 #!/bin/bash
 
-set -e
+set -E
+exec 3<&2 # preserve original stderr at fd 3
 
 abs_dirname() {
   local cwd="$(pwd)"
@@ -16,12 +17,15 @@ abs_dirname() {
   cd "$cwd"
 }
 
-log() {
-  if [ -z "$VERBOSE" ]; then
-    cat >>"$LOG_PATH"
-  else
-    tee -a "$LOG_PATH"
-  fi
+build_failed() {
+  { echo
+    echo "BUILD FAILED"
+    echo
+    echo "Inspect or clean up the working tree at ${TEMP_PATH}"
+    echo "Results logged to ${LOG_PATH}"
+    echo
+  } >&3
+  exit 1
 }
 
 install_package() {
@@ -47,14 +51,14 @@ download_package() {
 
   echo "Downloading ${package_url}..." >&2
   { curl "$package_url" > "${package_name}.tar.gz"
-  } 2>&1 | log
+  } >&4 2>&1
 }
 
 extract_package() {
   local package_name="$1"
 
   { tar xzvf "${package_name}.tar.gz"
-  } 2>&1 | log
+  } >&4 2>&1
 }
 
 build_package() {
@@ -80,14 +84,14 @@ build_package_standard() {
   { ./configure --prefix="$PREFIX_PATH"
     make -j 2
     make install
-  } 2>&1 | log
+  } >&4 2>&1
 }
 
 build_package_ruby() {
   local package_name="$1"
 
   { "$RUBY_BIN" setup.rb
-  } 2>&1 | log
+  } >&4 2>&1
 }
 
 build_package_rbx() {
@@ -95,7 +99,7 @@ build_package_rbx() {
 
   { ./configure --prefix="$PREFIX_PATH"
     rake install
-  } 2>&1 | log
+  } >&4 2>&1
 }
 
 build_package_copy() {
@@ -181,12 +185,20 @@ TEMP_PATH="/tmp/ruby-build.${SEED}"
 RUBY_BIN="${PREFIX_PATH}/bin/ruby"
 CWD="$(pwd)"
 
+exec 4<> "$LOG_PATH" # open the log file at fd 4
+if [ -n "$VERBOSE" ]; then
+  tail -f "$LOG_PATH" &
+  trap "kill 0" SIGINT SIGTERM EXIT
+fi
+
 export LDFLAGS="-L'${PREFIX_PATH}/lib' ${LDFLAGS}"
 export CPPFLAGS="-I'${PREFIX_PATH}/include' ${CPPFLAGS}"
 
 unset RUBYOPT
 unset RUBYLIB
 
+trap build_failed ERR
 mkdir -p "$TEMP_PATH"
 source "$DEFINITION_PATH"
 rm -fr "$TEMP_PATH"
+trap - ERR