variables in Perl need sigils, so it must be $i not just i

(using strict and warnings should have prevented you)

and you need to increment it with ++$i within the loop.

As an alternative you could just test $. % 2 since $. automatically holds the line-number.

Cheers Rolf

( addicted to the Perl Programming Language)

In reply to Re^3: find reverse complement of every 2nd line by LanX
in thread find reverse complement of every 2nd line by bingalee

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