The build didn't work if the directory temp didn't exist before.

h2/build.bat

 @echo off
 if "%JAVA_HOME%"=="" echo Error: JAVA_HOME is not defined.
-if exist bin/org/h2/build/Build.class goto buildOK
+if not exist temp mkdir temp
 if not exist bin mkdir bin
+if exist bin/org/h2/build/Build.class goto buildOK
 javac -sourcepath src/tools -d bin src/tools/org/h2/build/*.java
 :buildOK
 "%JAVA_HOME%/bin/java" -Xmx512m -cp "bin;%JAVA_HOME%/lib/tools.jar;temp" org.h2.build.Build %*
\ No newline at end of file

h2/build.sh

@@ -2,10 +2,13 @@
 if [ -z "$JAVA_HOME" ] ; then
   echo "Error: JAVA_HOME is not defined."
 fi
+if [ ! -d "temp" ] ; then
+  mkdir temp
+fi
+if [ ! -d "bin" ] ; then
+  mkdir bin
+fi
 if [ ! -f "bin/org/h2/build/Build.class" ] ; then
-  if [ ! -d "bin" ] ; then
-    mkdir bin
-  fi
   javac -sourcepath src/tools -d bin src/tools/org/h2/build/*.java
 fi
 "$JAVA_HOME/bin/java" -Xmx512m -cp "bin:$JAVA_HOME/lib/tools.jar:temp" org.h2.build.Build $@