Useful Bash functions to determine OS and more

In a number of my Bash aliases I need to check two constants: what sort of OS I’m on and whether it’s a production box or not. I use the former for aliases that allow me to install and search for packages across distributions, as described here. The latter I use to determine whether I am allowed to use aliases for turning off the machine and the like. The code I used to determine these before was repetitive and hard to work with. So I created functions to determine the values, allowing all the aliases to reference a single source.

The first function determines the OS I am on, in the general categories of “debian” and “redhat”:

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function cur_os {
# Attempts to check whether the local box is running Debian/Ubuntu
# (considered together as "debian") or Red Hat/CentOS (considered
# together as "redhat".
# Make sure we have egrep
EGREP_VER=`egrep --version | head -n 1`
if [[ "${EGREP_VER:0:8}" != "GNU grep" ]] ; then
echo "egrep isn't installed, sorry."
exit 1
fi
# Make sure we have /etc/issue
if [[ ! -r '/etc/issue' ]] ; then
echo "/etc/issue isn't readable."
exit 1
fi
# Run checks
DEB_OS=`egrep -i 'Ubuntu|Debian' /etc/issue`
RH_OS=`egrep -i 'CentOS|Red Hat' /etc/issue`
if [[ ${#DEB_OS} -gt 0 ]] ; then
CUR_OS="debian"
elif [[ ${#RH_OS} -gt 0 ]] ; then
CUR_OS="redhat"
else
CUR_OS="unknown"
fi
echo $CUR_OS
}

I chose these two categories because the package handler is the same within each. This could of course be expanded to more systems, these just happen to be the flavors I am always on. Just after I define this function I also include:

1	cur_os > /dev/null

This way the variable CUR_OS is populated each time Bash loads but the output doesn’t dirty up the prompt. Having this variable allows the definition of fairly elegant functions such as:

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function inst () {
# Installs passed packages.
case "$CUR_OS" in
'debian')
sudo apt-get install $@
;;
'redhat')
sudo yum install $@
;;
*)
echo "You are not on a supported OS."
;;
esac
}

This next function determines whether the current machine is one I consider non-production:

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function local_box {
# Checks if the current machine is one of my own machines (and thus
# less risky to run various commands on).
LOCAL_BOXES=( 'ZenSam' 'B74kb0x' 'MediaServer' 'shuckins-alienware' 'laptop-shuckins' )
CURRENTBOX=`hostname`
CUR_BOX_LOCAL=0
for i in ${LOCAL_BOXES[@]}; do
if [[ $i == ${CURRENTBOX} ]] ; then
CUR_BOX_LOCAL=1
fi;
done
echo $CUR_BOX_LOCAL
}
# So that CUR_BOX_LOCAL is set initially:
local_box > /dev/null

The idea is that LOCAL_BOXES holds hostnames of machines that aren’t as sensitive to things like shutting down. Then when you create aliases for such potentially destructive actions you define a safe form for the potentially sensitive boxes:

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if [[ $CUR_BOX_LOCAL == 1 ]] ; then
alias off="sudo shutdown -h now"
alias restart="sudo shutdown -r now"
else
alias off="echo 'You are on a remote box!'"
alias restart="echo 'You are on a remote box!'"
fi

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