To me, apart from the various points people have made about using warnings and strictures, structured code, using subroutines and so forth, the most important rule is:

Use meaningful names!

This applies to variables, subroutines, loops, filehandles, everything.

Always take a little extra time, 10 seconds or so, to name your variables well.

Good names can often make comments redundant and unnecessary.

I hope I never ever have to maintain a program again that's full of variables named @tmp, $i, $n, $ldr, %hash or subroutines named process or run and all the other meaningless crap people foist off as names.

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Regards,
Helgi Briem
helgi DOT briem AT decode DOT is