Launching a Perl one-liner within a shell system command launched itself by another Perl program seems to be poor design. If you really want to call a system command from your Perl script just issue this system command:

ps aux | grep java
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and process the output within your other Perl script with the commands you have in your one-liner. Although the filtering made by the grep shall command could itself be done within the Perl script. And then, of course, there are also some pure Perl solutions using modules.