Check your return values:

chdir("/home/code/") or warn "chdir failed!\n";
system("svm_classify zkereigenout.dat svmmodel.mod") and warn "system 
+failed: $!\n";
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(Yes, that second line should have "and warn". system has it's return values kinda backward.)

Try system("echo foo>svm_predictions") in place of your system call and see if that works (or fails giving meaningful information).