Installing packages if they don't exist in Bash

Question

This script simply installs the chosen packages if they're not present on a Linux system using the apt package manager. Notes on improvements of any aspect are welcome!

setup_env.sh

#!/usr/bin/env bash
set -euo pipefail

install_if_not_exist() {
  if dpkg -s "$1" &>/dev/null; then
    PKG_EXIST=$(dpkg -s "$1" | grep "install ok installed")
    if [ -z "$PKG_EXIST" ]; then
      sudo apt install "$1" -y
    fi
  else
    sudo apt install "$1" -y
  fi
}

sudo apt update -y

install_if_not_exist aria2
install_if_not_exist coreutils
install_if_not_exist gawk
install_if_not_exist jq
install_if_not_exist moreutils
install_if_not_exist sed

Answer 1

Good

• Yay for using a function to contain most of the functionality
• Good indentation
• It looks like you're following shellcheck
• Good names for the variable and function

Suggestions

• Use double square brackets for conditionals. They will lead to fewer surprises.
• Instead of repeating the sudo apt install "$1" -y I'd change the if [ -z "$PKG_EXIST" ]... to if [[ -n "$PKG_EXIST" ]]; then; return; fi and move the sudo apt install "$1" -y line to the bottom of the function definition. Coded more fully below.
• I like to comment the strict mode line(s) since many folks don't realize what this is doing.
• Check to make sure the function only gets one argument. You might later accidentally put a space into a package name and this would catch that.

rewrite of central function

install_if_not_exist() {
  if dpkg -s "$1" &>/dev/null; then
    PKG_EXIST=$(dpkg -s "$1" | grep "install ok installed")
    if [[ -n "$PKG_EXIST" ]]; then
      return
    fi
  fi
  sudo apt install "$1" -y
}

Answer 2

Using sudo in scripts is an anti-pattern. It can irritate the user with repeated password requests (depending on how sudo is configured).

For this script, it's better to assume (or test) that the user is already sufficiently privileged. And explicitly set PATH at the beginning to avoid trojan horses taking advantage of the escalated privilege:

PATH=/usr/sbin:/usr/bin

The only thing in this script that's not standard POSIX shell is set -o pipefail, so it could easily be made portable and more efficient.