How to write bash script without using sudo in it?

Question

How can I write a gem install or apt-get install in bash without letting it use sudo?

#!/usr/bin/env bash

apt-get update -y
apt-get upgrade -y
gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
\curl -sSL https://get.rvm.io | bash -s stable --ruby
source /usr/local/rvm/scripts/rvm
((EUID)) || exit
gem install jekyll

Answer 1

#!/usr/bin/env bash
((!EUID)) && { # check if the EUID is a zero 
  echo "${0##*/} can not be executed as root " # notify
  exit 1 # exist with status code 1
}
gem install jekyll

since you are an admin (normal user) the variable $EUID always greater than zero !
and in root $EUID = 0

((expression)) The expression is evaluated according to the rules described below under ARITHMETIC EVALUATION. If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to let "expression"

or

#!/usr/bin/env bash
[[ $EUID = 0 ]] && { # check if the EUID is eq to zero
  echo "${0##*/} can not be executed as root " # notify
  exit 1 # exist with status code 1
}
gem install jekyll

i prefer this one

((EUID)) || exit 1

or

((!EUID)) && exit 1

updates after question edit

#!/usr/bin/env bash
((!EUID)) && {
 #stuff to be exec as root
for option in update 'upgrade -y'
  do
    apt-get $option
  done
gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
\curl -sSL https://get.rvm.io | bash -s stable --ruby
source /usr/local/rvm/scripts/rvm

} || {
 #stuff to be exec as non-root
gem install jekyll

}
exit 0

now it will run in both root and non-root users but it will exec only a part of the script according to the EUID