See the Basic debugging checklist, the first item is to use warnings; use strict;. How to apply them to one-liners: hippo already mentioned -w, adding strict and diagnostics you get -wMstrict -Mdiagnostics:

$ perl -wMstrict -Mdiagnostics -e
  '"system(/usr/bin/perl /root/test.pl)"'
Useless use of a constant ("system(/usr/bin/perl /root/test."...) in
  void context at -e line 1 (#1)
    (W void) You did something without a side effect in a context that
    does nothing with the return value, such as a statement that
    doesn't return a value from a block, or the left side of a scalar
    comma operator.  Very often this points not to stupidity on your
    part, but a failure of Perl to parse your program the way you
    thought it would. ...
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