do not stop the program from running ... fork bomb still happens

True!

After futher consideration, I came up with many more habits, but few that are akin to the OP. I don't even like it (0 == $foo) myself; I use it in C, but am glad to not need it in Perl.
More of my habits:

• Strict and warnings, of course!
• Write in a Syntax Highlighting editor.
• Write at least one test ASAP, and run it frequently (roughly each time I hit Save).
• If I can't write normal tests (maintenance on a huge web package), at least get (WWW::Mechanize) the complete output of one sample run, and compare against *that* as my test.
• Align similar code, and write code that is alignable (until refactoring makes sense).
• Prefer to write Table or Data-driven code where possible.
• (Except when skipping out with next/last) Never write an if{}elsif{} without an else, even if it is just a documented '# Do nothing'.
• (During early development) Die at the drop of a hat. Don't just die where you see possible errors; use assertions on *everything* that you can predict the state of. Die on "Can't happen"!
• Make whitespace visible on diagnostic output: die "Foo '$foo' has an invalid value"; the single-quotes show me that $foo contains trailing whitespace.
• I copy a template to create each new program. In its top block is this line, to foil non-printables and buffering issues that confound debugging. The whole line is either commented on uncommented together: #use Data::Dumper; $Data::Dumper::Useqq=1; $|=1;.
• Examine the data during development, rather than waiting for debugging:

  # I want to write this:
  my @rows = @{ $dbh->selectall_arrayref($sql) };
  
  # Instead, I always write this, and remove the dump
  # after verifying the data and its format:
  my $rows_aref = $dbh->selectall_arrayref($sql) or die;
  print Dumper $rows_aref;
  my @rows = @{$rows_aref};
  [download]

  Hence I see early that each row is an arrayref (not the expected scalar), even though I only asked for one field in the select. 1 minute of checking my assumptions saved 15 minutes of later debugging.

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