Introduction to Bash Scripting
In Computer programming, a script is a set of commands for an appropriate run time environment that is used to automate the execution of tasks. A Bash Shell Script is a plain text file containing a set of various commands that we usually type in the command line. It is used to automate repetitive tasks on Linux filesystem.
A character sequence known as the "shebang" appears on the first line of Bash scripts. When the program loader executes the file, the shebang is the first instruction, and the characters indicate which interpreter to use when reading the script.
To indicate the use of the Bash interpreter, add the following line to the file:
#!/bin/bash
#! directs the program loader to load an interpreter for the code in the file.
/bin/bash the Bash interpreter's location.
if for example, we would like to use PowerShell interpreter, we will use "#!/usr/bin/pwsh".
Adding Comments
Lines that do not execute are referred to as comments. They do, however, aid in code readability. Add a comment after the shebang to explain what the script is.
H!/bin/bash
#This is a sample comment
#This is another commentAdding Code
Bash scripts are used to make our work more efficient by automating manual tasks. Let's write and run our first bash script.
H!/bin/bash
#This is a sample comment
#This is another comment
echo "This is our first script"
echo "The uptime of the system is:"
uptime
echo "Disk utilization is"
df -h
echo "Memory utilization"
free -mRun a script
in order to run a script, you will have to specify its absolute or relative path. Prior to running a script. you must ensure that the script has executable permission. Lets see an example:
[root@scriptbox scripts]# ./firstscript.sh
-bash: ./firstscript.sh: Permission denied
[root@scriptbox scripts]# ls -l
total 4
-rw-r--r--. 1 root root 213 Jun 19 10:41 firstscript.sh
As you can see, there is executable permission that is missing, adding and run the script:
[root@scriptbox scripts]# chmod +x firstscript.sh
[root@scriptbox scripts]# ls -l
total 4
-rwxr-xr-x. 1 root root 213 Jun 19 10:41 firstscript.shNow we can run it:
[root@scriptbox scripts]# ./firstscript.sh
./firstscript.sh: line 1: H!/bin/bash: No such file or directory
This is our first script
The uptime of the system is:
10:54:04 up 52 min, 1 user, load average: 0.00, 0.01, 0.05
Disk utilization is
Filesystem Size Used Avail Use% Mounted on
devtmpfs 485M 0 485M 0% /dev
tmpfs 496M 0 496M 0% /dev/shm
tmpfs 496M 6.7M 489M 2% /run
tmpfs 496M 0 496M 0% /sys/fs/cgroup
/dev/mapper/centos-root 50G 1.7G 49G 4% /
/dev/sda1 1014M 167M 848M 17% /boot
/dev/mapper/centos-home 28G 33M 28G 1% /home
vagrant 477G 148G 330G 31% /vagrant
tmpfs 100M 0 100M 0% /run/user/1000
Memory utilization
total used free shared buff/cache available
Mem: 990 110 451 6 429 736
Swap: 1023 0 1023Let's change the code to make it more readable:
H!/bin/bash
#This is a sample comment
#This is another comment
echo "This is our first script"
echo
echo "-------------------------------"
echo "The uptime of the system is:"
uptime
echo
echo "-------------------------------"
echo "Disk utilization is"
df -h
echo
echo "-------------------------------"
echo "Memory utilization"
free -mand let's run it:
[root@scriptbox scripts]# ./firstscript.sh
./firstscript.sh: line 1: H!/bin/bash: No such file or directory
This is our first script
-------------------------------
The uptime of the system is:
11:01:39 up 59 min, 1 user, load average: 0.00, 0.01, 0.05
-------------------------------
Disk utilization is
Filesystem Size Used Avail Use% Mounted on
devtmpfs 485M 0 485M 0% /dev
tmpfs 496M 0 496M 0% /dev/shm
tmpfs 496M 6.8M 489M 2% /run
tmpfs 496M 0 496M 0% /sys/fs/cgroup
/dev/mapper/centos-root 50G 1.7G 49G 4% /
/dev/sda1 1014M 167M 848M 17% /boot
/dev/mapper/centos-home 28G 33M 28G 1% /home
vagrant 477G 148G 330G 31% /vagrant
tmpfs 100M 0 100M 0% /run/user/1000
tmpfs 100M 0 100M 0% /run/user/0
-------------------------------
Memory utilization
total used free shared buff/cache available
Mem: 990 110 450 6 429 736
Swap: 1023 0 1023Automating Website Setup using bash script
in this example, I will use a bash script to deploy a website on a centos machine.
First, let's create the bash file under the script folder and open it using VIM editor
[root@scriptbox scripts]# vim websetup.shScript Details:
#!/bin/bash
# Installing Dependencies
echo "########################################"
echo "Installing packages."
echo "########################################"
sudo yum install wget unzip httpd -y > /dev/null
echo
# Start & Enable Service
echo "########################################"
echo "Start & Enable HTTPD Service"
echo "########################################"
sudo systemctl start httpd
sudo systemctl enable httpd
echo
# Creating Temp Directory
echo "########################################"
echo "Starting Artifact Deployment"
echo "########################################"
mkdir -p /tmp/webfiles
cd /tmp/webfiles
echo
wget https://www.tooplate.com/zip-templates/2098_health.zip > /dev/null
unzip 2098_health.zip > /dev/null
sudo cp -r 2098_health/* /var/www/html/
echo
# Bounce Service
echo "########################################"
echo "Restarting HTTPD service"
echo "########################################"
systemctl restart httpd
echo
# Clean Up
echo "########################################"
echo "Removing Temporary Files"
echo "########################################"
rm -rf /tmp/webfiles
echo
sudo systemctl status httpd
ls /var/www/html/lets test it by using the machine IP http://192.168.10.12/:
