$
$
$ cat file_1
1. aaa 1111
2. bbb 2222
3. ccc 3333
$
$
$ cat file_2
1111 "this is a test file "
2222 "you are in File 2"
$
$
$ perl -lne 'if ($ARGV eq "file_2"){/^(\d+)\s*(.*)$/ and $x{$1}=$2} else {/^.* (\d+)$/ and print "$_ ",$x{$1}//"\"Blah\""}' file_2 file_1
1. aaa 1111 "this is a test file "
2. bbb 2222 "you are in File 2"
3. ccc 3333 "Blah"
$
$