A simple script to update your ssh config file.

I’ve been reading about Bash scripting lately and finally thought of something useful. Below is a simple script that automates the addition of new hosts to your ssh config file. All you need to do is copy the script, save it as yourcommand.sh, set the execute bit with chmod +x yourcommand.sh, and place that file inside of the bin folder in your home directory (which you may have to create). Now you can can call that script from any directory and add a new host to the config file under /home/youruser/.ssh/.

This script will exit right away if you do not have an ssh config file already. Once created, rerunning the script will create a backup copy (which will be useful later on) and then prompt you for input. The only error checking in place right now is on the alias (Host) field. If you type a name you’ve used already, you’ll be prompted again until you provide a new name. Spaces in that field will not stop the script, but only the characters before the first space will be picked up as the alias. You shouldn’t have spaces in these names anyway. The other three fields will accept any input, including spaces, so be sure the information you input is correct for the field.

You’ll be shown the information as it will be written to the config file and asked to confirm. Yes will append the new host to your config file and the script will exit. No will drop the changes and the script will exit.

I know it’s a bit comment heavy so please drop anything you don’t need.

#SSH config - script to add a new host

#House Keeping-----------------------------------------------------------------

#clear the screen completely

#Look for ssh config in the default location, pipe to /dev/null to mute output
#Assign the exit status of cat to the check variable, for use in IF statement
cat $HOME/.ssh/config > /dev/null

#If ssh config exists, echo start message and continue script. Else, print error message and exit script
if [ ${check} == 0 ]; then
	echo "Let's add another host to your ssh config file"
	echo "You do not have an ssh config file yet. Create one and rerun this script."
	sleep 2
	exit 1

#Main script - User Input-------------------------------------------------------

#Ask the user to input the ssh host alias
#You must enter a new name before this variable will be output to any files
read -p "Enter the host name alias: " sshalias
grep -q ${sshalias} $HOME/.ssh/config
check=$? # this assigns the exit code of grep, for use in while loop

#Check the results of grep, if we found that name already exists (grep exit code 0) then we request a new name until the user provides something unique 
while [ ${check} == 0 ]; do
	read -p "Enter the host name alias (It must be new): " sshalias
	grep -q ${sshalias} $HOME/.ssh/config

#Ask the user for the IP adress of the ssh host
#Be mindful that there are no validity checks here
read -p "Enter IP address or host name: " sshaddress

#Ask the user for the ssh port of the new host
#The default is 22, if no vlaue is given, default is used
#If input is given, the default will not be used
#Be mindful that there are no validity checks here
read -p "Enter the ssh port [22]: " sshport

#Ask the user for the log in user name for the new host
#Be mindful that there are no validity checks here
read -p "Enter the ssh user name: " sshuser

#Confirmation from user and write out to files----------------------------------

#Print out the values that will be added to the config files and ask for confirmation
echo "The following will be added to your ssh config file:"
echo -e "Host ${sshalias}\nHostName $sshaddress\nPort ${sshport}\nUser ${sshuser}\n"
read -p "Is this information correct? Y/N: " confirmation

#Check confirmation input, if y then write new changes out to ssh config
if [ "${writeconf}" == "y" ]; then
	#Make a copy of the current file before we start making additions
	cp $HOME/.ssh/config $HOME/.ssh/config.bak
	#echo out the new host information
	echo -en '\n' >> $HOME/.ssh/config
	echo "Host ${sshalias}" >> $HOME/.ssh/config
	echo -e "\tHostName ${sshaddress}" >> $HOME/.ssh/config
	echo -e "\tPort ${sshport}" >> $HOME/.ssh/config
	echo -e "\tUser ${sshuser}" >> $HOME/.ssh/config
	#Confirm the new host was added 
	echo -e "\nNew host added to ssh config!"
	sleep 2
	echo -e "\nDropping changes. Please run this script again to add new hosts."
	sleep 2

exit 0

Hope this is useful to someone else out there. I am really enjoying it, and now I can officially say I’ve written a Bash script!