I guess you don't have enough memory for using File::Tie on a 500GB file, since it sluprs the entire file.

Uhhhhmmmmm... no it don't! From the File::Tie man page:

The file is not loaded into memory, so this will work even for gigantic files.

I even remember looking at the source code for this module once to validate that statement. I used to think that the module loaded the whole file into memory but it doesn't.

However, there is a lot of overhead associated with File::Tie for certain operations. For instance I had some code once that looked something like:

# considering @ry was the tie'd array:
my $last_line = $#ry + 1;
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and found that if I visited that line multiple times it slowed my code way down. Just FWIW...