It's going through all the elements of @lines except the last one. $#lines is the index of the last element of @lines. So 0..($#lines - 1) is therefore the range from zero to index of the next-to-last element. So @lines[0..($#lines - 1)] is a slice of all but the last element.
Caution: Contents may have been coded under pressure.

In reply to Re^3: While.For loop noob query by Roy Johnson
in thread While.For loop noob query by jriggs420

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