Print the empty string prints nothing. Printing a newline prints an empty line.

my @history = ('') x 3;
while (<>) {
    print @history, $_ if /pattern/;
    push @history, $_;
    shift @history;
}
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or

my @history = ('') x 4;
while (<>) {
    push @history, $_;
    shift @history;
    print @history, $_ if /pattern/;
}
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