I am using awk to filter output returned by a previous command (docker image ls) which is tab separated columns.

I would like to print the first 2 columns with a : in between.

What I've tried:

`docker image ls | awk '{ print $1\:$2}'`

But no matter how I tried to print $1 and $2 I still get 

```
awk: syntax error at source line 1
 context is
    { print $1 >>>  \ <<< \ $2}
awk: illegal statement at source line 1

```

How can I use : in the output?

Thanks!