GDB attach to a running process in batch mode

Ever needed to attach to a running process in a gdb batch mode script but didn’t know the process’ PID in advance? You can use GDB’s built-in Python interpreter to do the heavy lifting for you. Put the following in your batch-mode script:
python gdb.execute("attach " + os.popen('pgrep <process name>').read().rstrip())
<gdb commands go here>
detach
quit

Then run as follows:
gdb --batch -x <script>

Magic!