Question: When retrieving data from Firebase, we typically use the code below (or some reiteration of it)

```
...observeSingleEvent(of: .value, with: { snapshot in

var tempPosts = [PostModel]()

for child in snapshot.chidren{
}

return tempPosts

})

```

but I don't exactly get what this code is doing? Can someone explain it on a high level? I've tried printing data on mulitple spots but the only data I'm getting is: Snap post or [App.PostModel]

Answer: 
all you need is:

```
awk '!/^chr(Un|M)/' file

```
In bash, you can do the comparison like this (assuming `line` contains a single line of the file, i.e. I've excluded the loop over the file's lines here):

```
if [[ $line != chrUn* ]] && [[ $line != chrM* ]]; then
    echo $line
fi;

```