That's not "strange language"; it's a Windows batch file. YOu probably don't need to change that at all, you just need to start it with "catalina.bat jpda start" instead of "catalina.bat start". I don't use the Eclipse integration, so can't say how that interacts, but I'd think that Eclipse has options to run Tomcat in debug (a.k.a. jpda) mode. If it doesn't, run Tomcat independently of Eclipse (which is what I advise anyway).
To reinforce what Tim Moores said, you don't have to change anything in the catalina.bat file. Just launch it with the "jpda start" command options.
You can override what port and other options JPDA will use by setting the appropriate environment variables, but usually you will not want to do that.
In Eclipse, create a Remote Debugging profile off the run/debug menu and set the target port and hostname to point to the instance of Tomcat running under JPDA. The default port is 8000.
Don't set any debugging options in the CATALINA_OPTS or setenv.bat (if you're using one). Everything you need is in the JPDA script options.
You have the option to start Tomcat in a paused state so that the debugger can connect before Tomcat starts (using the debugger resume command), or have Tomcat start normally and connect on the fly. Unless you need to debug stuff that's in initialization code, it's usually easier to leave it unpaused, but that's up to you.
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