Running a command inside a singularity container

Question

This is probably very easy, but I am very new to singularity containers, any help appreciated. I have the following definition file:

Bootstrap: docker
From: ubuntu:20.04

%post
  apt-get -y update
  apt-get -y upgrade
  apt-get -y install wget
  wget https://sourceforge.net/projects/bbmap/files/BBMap_39.03.tar.gz
  tar -zxvf BBMap_39.03.tar.gz

%environment
    PATH=$PATH:bbmap/

%runscript
    exec "$@"

And I would like to execute a command within bbmap called filterbyname.sh.

I just built the container (I am using a vagrant virtual machine on MacOS):

sudo singularity build test.sif test.def

but it seems that the only way that I can execute things is with sudo:

sudo singularity exec test.sif filterbyname.sh

I think it is as singularity is creating everything under /root/

I would like to have this container so that I can use it elsewhere without sudo privileges. What am I missing? Any suggestions?