note TheDamian <blockquote><i> The problem in this case is not really about whether the program is re-runnable, but about the fact that it corrupts your data. </i></blockquote> Neither of which is what the original recommendation is about. That recommendation, as it appears in "Perl Best Practices" is: <blockquote><b> <font size="+1">In-situ Arguments</font> <hr> <p align="center">Allow the same filename to be specified for both input and output. <hr> </b></blockquote> And that most definitely <em>is</em> a best practice. <p>The issue raised here is that one of the two solutions suggested in the book is apparently more limited in applicability than I indicate in the text (a deficiency I have already mentioned that I'll be remedying as soon as I can). <p>Now it may well be that "Perl Best Practices" would benefit from the addition of an extra guideline; one that suggests using a transactional approach to avoid corrupting data. But that's only peripherally related to this guideline. It should definitely be a <em>separate</em> suggestion, since the problem of data corruption is not unique to opening the same file twice. 488824 488839