Shell Programming and Scripting

I did a search before posting and couldn't find an example of what I need done. Anyway, I have a file called file1.txt, which has data like this:

File2.txt contains:
So what I need to do is from file1.txt find the first line M977 in file2.txt and replace the line below it with the line from file1.txt. So file2.txt would look like this.

I would need to loop though file1.txt and continue though each line. The next pass would fine M998 in file2.txt and change the line below it with the line from file1.txt. Hope this makes sense.

Code:

awk 'NR==FNR{x=$0;getline;a[x]=$0;next} 
{if($0 in a){x=$0;print x;print a[x];getline}else{print}}' file1 file2

--ahamed

Code:

kent$  awk 'NR==FNR{if(NR%2)getline a[$0]} NR>FNR{if($0 in a){i=$0;print;next;} if(a[i]){$0= a[i];i=0} print $0}' file1.txt file2.txt
T55
12
M977
57 62 78 94 96 107
T90
01 88
M1117
61 62 01 92 33 14

Hey guys, thanks for the reply. sk1418 - looks like yours is working, at least I can see it printing out the correct values. It's just that file2.txt isn't being over written with the new lines. How do you over write file2.txt to contain the new lines?