How to add code to .bashrc without causing errors?

I'm learning how to passthrough my NIC to my KVM.

This guide https://mathiashueber.com/passthrough-windows-11-vm-ubuntu-22-04/ says to add the following code to the file ~/.bashrc

#!/bin/bash
# change the 999 if needed
shopt -s nullglob
for d in /sys/kernel/iommu_groups/{0..999}/devices/*; do
    n=${d#*/iommu_groups/*}; n=${n%%/*}
    printf 'IOMMU Group %s ' "$n"
    lspci -nns "${d##*/}"
done;

I'm unclear where the code should be inserted, so it's in lines 1-8.

  1 #!/bin/bash
  2 # change the 999 if needed
  3 shopt -s nullglob
  4 for d in /sys/kernel/iommu_groups/{0..999}/devices/*; do
  5 n=${d#*/iommu_groups/*}; n=${n%%/*}
  6 printf 'IOMMU Group %s ' "$n"
  7 lspci -nns "${d##*/}"
  8 done;
  9
 10 # ~/.bashrc: executed by bash(1) for non-login shells.
 11 # see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)
 12 # for examples
 13
 14 # If not running interactively, don't do anything
 15 case $- in
 16 *i*) ;;
 17 *) return;;
 18 esac
 19
 20 # don't put duplicate lines or lines starting with space in the history.
 21 # See bash(1) for more options
 22 HISTCONTROL=ignoreboth
 23
 24 # append to the history file, don't overwrite it
 25 shopt -s histappend
 26
 27 # for setting history length see HISTSIZE and HISTFILESIZE in bash(1)
 28 HISTSIZE=1000
 29 HISTFILESIZE=2000
 30
 31 # check the window size after each command and, if necessary,
 32 # update the values of LINES and COLUMNS.
 33 shopt -s checkwinsize
 34
 35 # If set, the pattern "**" used in a pathname expansion context will
 36 # match all files and zero or more directories and subdirectories.
 37 #shopt -s globstar
 38
 39 # make less more friendly for non-text input files, see lesspipe(1)
 40 [ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"
 41
 42 # set variable identifying the chroot you work in (used in the prompt below)
 43 if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
 44 debian_chroot=$(cat /etc/debian_chroot)
 45 fi
 46
 47 # set a fancy prompt (non-color, unless we know we "want" color)
 48 case "$TERM" in
 49 xterm-color|*-256color) color_prompt=yes;;
 50 esac
 51
 52 # uncomment for a colored prompt, if the terminal has the capability; turned
 53 # off by default to not distract the user: the focus in a terminal window
 54 # should be on the output of commands, not on the prompt
 55 #force_color_prompt=yes
 56
 57 if [ -n "$force_color_prompt" ]; then
 58 if [ -x /usr/bin/tput ] && tput setaf 1 >&/dev/null; then
 59 # We have color support; assume it's compliant with Ecma-48
 60 # (ISO/IEC-6429). (Lack of such support is extremely rare, and such
 61 # a case would tend to support setf rather than setaf.)
 62 color_prompt=yes
 63 else
 64 color_prompt=
 65 fi
 66 fi
 67
 68 if [ "$color_prompt" = yes ]; then
 69 PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
 70 else
 71 PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
 72 fi
 73 unset color_prompt force_color_prompt
 74
 75 # If this is an xterm set the title to user@host:dir
 76 case "$TERM" in
 77 xterm*|rxvt*)
 78 PS1="\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
 79 ;;
 80 *)
 81 ;;
 82 esac
 83
 84 # enable color support of ls and also add handy aliases
 85 if [ -x /usr/bin/dircolors ]; then
 86 test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
 87 alias ls='ls --color=auto'
 88 #alias dir='dir --color=auto'
 89 #alias vdir='vdir --color=auto'
 90
 91 alias grep='grep --color=auto'
 92 alias fgrep='fgrep --color=auto'
 93 alias egrep='egrep --color=auto'
 94 fi
 95
 96 # colored GCC warnings and errors
 97 #export GCC_COLORS='error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01'
 98
 99 # some more ls aliases
100 alias ll='ls -alF'
101 alias la='ls -A'
102 alias l='ls -CF'
103
104 # Add an "alert" alias for long running commands. Use like so:
105 # sleep 10; alert
106 alias alert='notify-send --urgency=low -i "$([ $? = 0 ] && echo terminal || echo error)" "$(history|tail -n1 |sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"'
107
108 # Alias definitions.
109 # You may want to put all your additions into a separate file like
110 # ~/.bash_aliases, instead of adding them here directly.
111 # See /usr/share/doc/bash-doc/examples in the bash-doc package.
112
113 if [ -f ~/.bash_aliases ]; then
114 . ~/.bash_aliases
115 fi
116
117 # enable programmable completion features (you don't need to enable
118 # this, if it's already enabled in /etc/bash.bashrc and /etc/profile
119 # sources /etc/bash.bashrc).
120 if ! shopt -oq posix; then
121 if [ -f /usr/share/bash-completion/bash_completion ]; then
122 . /usr/share/bash-completion/bash_completion
123 elif [ -f /etc/bash_completion ]; then
124 . /etc/bash_completion
125 fi
126 fi

However this causes an error when running .bashrc with the command ./.bashrc

ubuntu@ubuntu:~$ ./.bashrc
./.bashrc: line 17: return: can only `return' from a function or sourced script