To creating an index of line numbers is fairly easy using a hash. For this you need a unique key for each line - the line number fits the bill. To create the index, loop through reading the file and store the position of each line. For example:

while (<FH>) {
    push @index, tell(FH);
}
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$. is the current line number, and tell returns the offset. The array can now be stored using different methods, including Data::Dumper. You could use a hash instead if you wanted to use a key other than the line-number.