from  perldoc -f delete

Deleting an array element effectively returns that position of the arr
+ay to its initial, uninitialized state.  Subsequently testing for the
+ same element with exists() will return false.  Note that deleting ar
+ray elements in the middle of an array will not shift the index of th
+e ones after them down--use splice() for that.  See "exists".
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The array has not shrunk in size.

#!/usr/bin/perl -w

my @array = (1, 2, 3, 4);

print "length = ", scalar @array,$/;

delete $array[2];

print "length = ", scalar @array,$/;
__END__
length = 4
length = 4
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If it is just the second element (index = 1) then you can also do this simple assignment and shift. If you want to move around quite freely use splice.

infile

first
second
third
fourth
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use Tie::File;

my $file = "file.csv";

tie my @lines, Tie::File, $file or die "can't update $file: $!";
$lines[1] = $lines[0];
shift(@lines);
untie @lines;
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outfile

 
first
third
fourth
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