I have a text file with a sentences, words on each line. E.g. 

```
Hello 
Hi 
How are you?
%
$
9

```

I need to remove the lines from the above file which contains non text characters. My output should be as follows:   

```
Hello 
Hi 

```

I am trying out this using awk command as follows:

```
awk '!/[%$0-9?]/' filename

```

I am able to do this for the above file because I know the special characters in above sentence. But, my file has a list of special characters that is difficult to write in awk.

I tried out the below commands but it keeps the lines that have both alphabets and special characters.

```
awk '/[a-zA-Z]/' filename

```

Hence, could anyone please suggest me how to write awk command that will keep only those lines that don't have any special characters OR how to keep only those lines that have alphabets only.

Thanks