OPatch needs Java. Set JAVA_HOME or ensure your system Java is compatible. For Oracle homes, use the built-in JRE:
He opened his browser, the cursor blinking expectantly in the search bar. He typed the lifeline:
From the results, select the version that matches (or the latest available in the 13.9.4.2.x series for your specific platform, such as Linux x86-64 or Windows). Click Download and save the .zip file to your server. Why You Need Version 13.9.4.2.5
[arthur@thebeast OPatch]$ ./opatch version
The results loaded. Most were Oracle Support links (MOS), requiring a login he had to dig out of a sticky note on his second monitor. He clicked the first relevant link: Document 2243445.1 - Latest OPatch Version Information.