sed - copy paste a line into another file at the same position in bash -

i want copy line 30 1 specific file , paste line 30 in file. cannot manually because files big (20 gb+)

i have found out how append end of file:

awk 'nr==30' file1.txt >> file2.txt 

how specify line file2?

you can't using redirection mechanism. perhaps suggest perl script (or awk, given you're using awk already), reads line, writes it, , slips new line in @ appropriate place.

my $count = 0; while (<input>) {    print output $_;    if ($count  == 30) {       print output $linetobeinserted;    }    $count++; } 

note how doesn't store whole file in memory merely each line @ time.