If by 'efficient' you mean 'a one liner' then this is what you are looking for:

perl -pe 'print "_" if $a++;' -i.bak yourfile.txt

[download]

Lookup perlrun for more detail on what's going on there.

____________________
Jeremy
I didn't believe in evil until I dated it.

In reply to Re: modifying and overwriting a file by jepri
in thread modifying and overwriting a file by mndoci

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