I have a file that looks like this: 

```
....
....
....
MY_TAG=Release_X_Y
....
....

```

The fourth line always looks like this and contains numbers. E.g. Release\_1\_1

The value I will have is an argument passed by a user which will look like this:

```
1_2_3 

```

Where 1, 2, 3 will always be seperated by underscores but will be changing numbers.

I need to take those first two numbers i.e. 1 and 2 and use them to replace the line MY\_TAG in my text file. Is it possible to do this with sed or awk?

**To summarise:** 

Pre-existing file

```
....
MY_TAG=Release_1_2  <---Line 4
....

```

User passes argument to my script and its stored as a variable:

```
User arg = 4_9_2

```

I want to modify the file mentioned above to be:

```
....
MY_TAG=Release_4_9
....

```