Scripting

Bash Scripting

A bash shell script is a file that holds a set of bash commands to be read and executed by Bash.

Bash files are commonly denoted with a .sh file extension for example: example-script.sh.

Additionally the first line of a Bash script commonly contains a shebang. A shebang is a line that informs the operating system of the exact shell to use when executing the script. The shebang simply points to the absolute path of the shell.

For example: #!/bin/bash.

Examples

The following examples are complete bash scripts that can be executed on any machine with the bash package.

Create new directory/new file script

The first example:

1. navigates to a specific directory
2. creates a new directory
3. changes into the new directory
4. creates a new file

Create a new file called create-dir-file.sh and add the following contents:

#!/bin/bash

## navgiate to /home/student/Desktop
cd /home/student/Desktop

## create new directory inside of /home/student/Desktop
mkdir new-directory

## navigate to  new-directory inside of /Desktop
cd new-directory

## create new file inside of new-directory
touch new-file

Execute the script by invoking the bash package and providing the path to the newly created script as the argument:

bash create-dir-file.sh

Upon creating and executing the create-dir-file.sh script a new directory and file will be created in one fell swoop!

Look at the contents of the /home/student/Desktop and /home/student/Desktop/new-directory directories.

LaunchCode Employee Script

The first script was pretty basic. Let’s create a more complex script that combines multiple tools we’ve learned in this class. Let’s scrape, extract, and transform some data into a more usable state.

The LaunchCode website provides an about page, and on the page is a listing of all current LaunchCode employees.

It looks similar to the following image:

Say we want a script that will:

1. make a request for the raw HTML
2. extract the data we want with grep
3. trim the data using sed
4. write the output to a new file

The file the script will be requesting is found at the link of the following attachment.

By hovering over the file you can find the URL of this specific resource, in the bottom left corner of your web browser.

Create a new file called lc-employee.sh and add the following code:

cd /home/student/Desktop

mkdir launchcode-roster

cd launchcode-roster

wget http://lctt-linux.netlify.app/bash-scripting/walkthrough/script/_index.files/about.html

cat about.html | grep '<p style="line-height: 1.4;"><strong>.*</strong><br/>.*<br/>' | sed 's/^.*<strong>//g' | sed 's/<\/strong><br\/>/: /g' | sed 's/<br\/>.*$//g' > lc-employees.txt

cat lc-employees.txt | grep "^John\|Paul" > john-paul.txt

Execute the newly created script:

bash lc-employee.sh

Output:

Script Validation

Check to see if the script worked!

• Navigate to your Desktop folder to view the newly created launchcode-roster directory.
• cd into the launchcode-roster directory and list the contents.
• cat out of the contents of the john-paul.txt

Recap:

• Bash scripting description
  • #!/bin/bash: shebang
• Example Bash Scripts:
  • Script to change directories, create a new directory, add a file to new directory
  • Script to create a list of LaunchCode Employees and also separate John and Paul from the list!