If you are on *nix, you could just use the split command: 
split -l 500 file.txt

[download]
This will dump out a lot of new files in your current directory (40 files to be exact: 20000/500).

If you want to use perl, you can make use of the special variable (INPUT_LINE_NUMBER): $.

In reply to Re: split file at line number by toolic
in thread split file at line number by Anonymous Monk

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