On a typical Ubuntu system, `/etc/issue` contains
```
Ubuntu 22.04.1 LTS \n \l
```
so `cat /etc/issue` tells you all you need to know. On Fedora/Rocky (and presumably
RHEL, but I'm not wealthy enough to test), it contains
```
\S
Kernel \r on an \m (\l)
```
which is not much help. What does `\S` expand to?

The information you want is in `/etc/os-release`. For example
```
NAME="Fedora Linux"
VERSION="38 (KDE Plasma)"
ID=fedora
VERSION_ID=38
VERSION_CODENAME=""
PLATFORM_ID="platform:f38"
PRETTY_NAME="Fedora Linux 38 (KDE Plasma)"
ANSI_COLOR="0;38;2;60;110;180"
LOGO=fedora-logo-icon
CPE_NAME="cpe:/o:fedoraproject:fedora:38"
DEFAULT_HOSTNAME="fedora"
HOME_URL="https://fedoraproject.org/"
DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f38/system-administrators-guide/"
SUPPORT_URL="https://ask.fedoraproject.org/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Fedora"
REDHAT_BUGZILLA_PRODUCT_VERSION=38
REDHAT_SUPPORT_PRODUCT="Fedora"
REDHAT_SUPPORT_PRODUCT_VERSION=38
SUPPORT_END=2024-05-14
VARIANT="KDE Plasma"
VARIANT_ID=kde
```
So we know this is fedora. Note that we can source this as a shell script.
Then we can do for example
```
( . /etc/os-release; echo "$PRETTY_NAME"; )
```
or even define
```
os_detail() { ( . /etc/os-release; echo "${!1}"; ); }
```
so that we can do
```
os_detail NAME
```
to get the os name.