How to detect OS system using BASH? - bash

Question

The script should be able to detect the operating system that is running.
The alternatives OS is Arch Linux, Centos and Ubuntu.
os=$(uname)
if [ "$os" == "Arch" ]; then
echo "Arch Linux detected"
elif [ "$os" == "CentOS" ]; then
echo "CentOS detected"
elif [ "$os" == "Ubuntu" ]; then
echo "Ubuntu detected"
else
echo "Unknown OS detected"
fi```
Output: Unknown OS detected
I tried doing this:
\`del1()
{
os=$(cat /etc/os-release | grep "PRETTY_NAME")
}
del1
echo "The operating system is: $os"\`
The output: PRETTY_NAME="Ubuntu 20.04.2 LTS"
But I want to check between Centos, Arch Linux and Ubuntu.
Any suggestions?

Answer 1

The uname command will always return Linux when running on Linux, so of course that's never going to work.
Using /etc/os-release is probably the best solution, but don't grep it for information; the file is a collection of shell variables that you can source with the . command, so you can write something like this:
#!/bin/sh
. /etc/os-release
case $ID in
ubuntu) echo "This is Ubuntu!"
;;
arch) echo "This is Arch Linux!"
;;
centos) echo "This is CentOS!"
;;
*) echo "This is an unknown distribution."
;;
esac

Answer 2

You can use the grep command to filter the output of the cat /etc/os-release command for specific strings that indicate the operating system.
For example, you could use the following command to check for Ubuntu:
os=$(cat /etc/os-release | grep -o "Ubuntu")
You could then use an if statement to check if the variable os equals to Ubuntu:
if [ "$os" == "Ubuntu" ]; then
echo "Ubuntu detected"
else
echo "Not Ubuntu detected"
fi
You can do the same to check for Arch Linux:
os=$(cat /etc/os-release | grep -o "Arch")
And for Centos:
os=$(cat /etc/os-release | grep -o "CentOS")
You can also use cat /etc/*-release instead of cat /etc/os-release for more general detection of the OS.
You can also use lsb_release -a command to get more details about the distribution and version of the OS.
os=$(lsb_release -a | grep -o "Ubuntu")
You can then create a function that check for each os one by one and print the output accordingly.
check_os(){
os=$(cat /etc/os-release | grep -o "Ubuntu")
if [ "$os" == "Ubuntu" ]; then
echo "Ubuntu detected"
else
os=$(cat /etc/os-release | grep -o "Arch")
if [ "$os" == "Arch" ]; then
echo "Arch Linux detected"
else
os=$(cat /etc/os-release | grep -o "CentOS")
if [ "$os" == "CentOS" ]; then
echo "CentOS detected"
else
echo "Unknown OS detected"
fi
fi
fi
}
check_os
Please note that this approach might not be 100% accurate and it is better to use the appropriate package manager commands to check the OS version and distribution.

Answer 3

If you just need to check the name of the OS, you can try;
source /etc/os-release
echo "The operating system is: $NAME"