[oracle@perass back]$ cat a.txt 
aaaaa
1
aaaaa
2
aaaaa
3
aaaaa
4
aaaaa
5
aaaaa
11111
[oracle@perass back]$ cat a1.pl 
open (A,"<","a.txt");
while (<A>){
    $num++;
    if ( $_ =~/aaaaa/ ){ $a=$num};
    if ($. == $a + 1){print "$_\n"};
}
[oracle@perass back]$ perl a1.pl 
1

2

3

4

5

11111