Linux: bash functions I use in my shell scripts

Good evening, today I decided to share a few of the bash functions I use in my shell scripts. I explain what each one does. These are tiny functions, easy to understand and modify if needed. You can also download the complete file of functions from the contributions page.

scpcopy: This bash function copies files over SCP and supports a non-standard SSH port:

function scpcopy()
{
host_ip="$1"
scpuser="$2"
scp_port="$3"
file2cp="$4"
dir2cp="$5"
scp -oPort="$scp_port" "$file2cp" "$scpuser"@"$host_ip":"$dir2cp"
}


remotereplace: This bash function performs a replacement with sed over SSH, with support for a non-standard SSH port:

function remotereplace()
{
host_ip="$1"
filetomodify="$2"
remoteport="$3"
src="$4"
dst="$5"
ssh -l root -p "$remoteport" "$host_ip" "sed -i \"s#$src#$dst#g\" $filetomodify"
}

remoteexec: This bash function executes a remote command over SSH and supports a non-standard SSH port.

function remoteexec()
{
host_ip="$1"
remoteport="$2"
command2exec="$3"
ssh -l root -p "$remoteport" "$host_ip" "$command2exec"
}

keygen: This bash function simply generates an SSH key pair remotely for the root account, with support for a non-standard SSH port.

function keygen()
{
host_ip="$1"
ssh -l root -p "$ssh_port" "$host_ip" "ssh-keygen -t rsa -f /root/.ssh/id_rsa -q -P \"\""
}

renhost: This bash function renames a Linux host (works on Debian Stretch)

function renhost()
{
echo -e "${YELLOW} [WARNING]" "${NC} Hostname doesn't match the actual server host, changing server hostname in progress..."
oldhost=$(grep "$ip" /etc/hosts)
newhost="$ip $sxhostcode $hostcode"
$replacer $repoptions "s#$oldhost#$newhost#" /etc/hosts
$replacer $repoptions "s#$HOSTNAME#$hostcode#" /etc/hostname
$replacer $repoptions "s#root@$HOSTNAME#root@$hostcode#" /etc/ssh/*.pub
hostname "$hostcode"
hostnamectl set-hostname "$hostcode"
}

checkip: This bash function checks that a variable contains an IP address.

function checkip()
{
if [[ "$1" =~ (([01]{,1}[0-9]{1,2}|2[0-4][0-9]|25[0-5])\.([01]{,1}[0-9]{1,2}|2[0-4][0-9]|25[0-5])\.([01]{,1}[0-9]{1,2}|2[0-4][0-9]|25[0-5])\.([01]{,1}[0-9]{1,2}|2[0-4][0-9]|25[0-5]))$ ]];
then
echo -e "${GREEN} [ OK ]" "${NC} IP address $1 is ok, install in progress..."
else
echo -e "${RED} [ ERROR ]" "${NC} $1 is not an IP address"
exit 0
fi
}

checkfqdn: This bash function checks that a variable contains a valid FQDN.

function checkfqdn()
{
result=$(echo "$1" | grep -P '(?=^.{1,254}$)(^(?>(?!\d+\.)[a-zA-Z0-9_\-]{1,63}\.?)+(?:[a-zA-Z]{2,})$)')

if [[ -z "$result" ]]
then
echo -e "${RED} [ ERROR ]" "${NC} $1 is not a valid FQDN"
exit 0
else
echo -e "${GREEN} [ OK ]" "${NC} $1 is a valid FQDN, install in progress..."
fi
}

checkuid: This bash function checks that a UID matches the expected value.

function checkuid()
{
if [ "$UID" -ne "$1" ]

then
echo -e "${RED} [ ERROR ]" "${NC} you must be root to install the server"
exit 0

else
echo -e "${GREEN} [ OK ]" "${NC} UID ok, install in progress..."

fi
}

changuserpass: This bash function simply changes a Linux user's password.

function changeuserpass()
{
user_pass="$1"
user="$2"
echo -e "$user_pass\n$user_pass" |passwd "$user"

}


sslinstall: This bash function installs a Let's Encrypt certificate for a vhost. Note: a server-wide alias to /home/letsencrypt avoids problems caused by client configurations such as .htaccess files.

function sslinstall()
{
admin_mail="$1"
domains="$2"
certbot -n --agree-tos --email "$admin_mail" --installer apache --webroot -w "/home/letsencrypt" --domains "$domains"
}


addmyuser: This bash function simply adds a new Linux user.

function addmyuser()
{
user="$1"
directory="$2"
useradd "$user" --shell /bin/bash -g users -m -d "$directory"
}


deploy: this bash function downloads and installs packages using apt.

downloader='apt -y -f --allow-unauthenticated -d install'
installer='apt -y -f --allow-unauthenticated install'

function deploy()
{
installer="$1"
packs="$2"

echo "Installing packages : $packages..."
$downloader $packs
$installer $packs
}

clean: this bash function empties a file, then deletes it

function clean ()
{
file2clean=$1
> "$file2clean"
rm -f "$file2clean"
}

genpass: this bash function generates a random password with the number of characters you specify

function genpass()
{
charx="$1"
pwgen -A -B "$charx" 1
}

writefile: This bash function writes to a file with 2 options: creating a new file or appending lines to an existing one.

 
Christophe Casalegno
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