export JAVA_HOME=....

$JAVA_HOME/bin/java -jar $JAVA_HOME/demo/jfc/Notepad/Notepad.jar -XX:+Print &
PID=$!
gcore -o /tmp/core $PID
kill $PID
$JAVA_HOME/bin/jinfo -flag PrintGC $JAVA_HOME/bin/java /tmp/core.$PID

<Here Usage message is printed>

but something like "+PrintGC" expected.

$JAVA_HOME/bin/jinfo $JAVA_HOME/bin/java /tmp/core.$PID

works fine.