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1. Introduction to operating systems
While web developers primarily focus on coding web applications and front-end development, having a good grasp of operating systems is essential for ensuring the compatibility, security, performance, and reliability of their applications, as well as for troubleshooting and optimizing various aspects of web development.
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2. Introduction to data networks
Networking is an integral part of web development because web applications rely on network communication to function. A solid understanding of networking concepts and practices is essential for building secure, performant, and reliable web applications.
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3. The shell. Linux commands
Knowing Linux commands for a system administrator or even a software developer is of utmost importance because most servers run on a Linux or Unix operating system.
- 3.1 ls : showing files
- 3.2 file permissions
- 3.3 mkdir. Creating directories
- 3.4 rmdir. Deleting directories
- 3.5 Moving/renaming files and directories
- 3.6 Other commands
- 3.7 Mounting units
- 3.8 Daemons
- 3.9 What processes are running?
- 3.10 Who am I and where am I?
- 3.11 Files has its owner
- 3.12 Other commands
- 3.13 Users
- 3.14 The /etc/passwd file
- 3.15 The /etc/group file
- 3.16 Links
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4. Shell script
In this chapter I want you to learn shell script but based on examples. Once you see the example I will propose another very similar one. If you do it and it works great, that means that not only do you understand the exercise but you are able to perform similar exercises. Keep in mind that with shell scripts you have to be patient. Misplaced whitespace can even cause a script to not work. If that happens, take a deep breath, be patient and persist, you will surely find the solution to the problem.
- 4.1. Your first shell script
- 4.2. Adding comments to your shell script
- 4.3. Variables in bash
- 4.4. Functions in bash
- 4.5 Conditional sentences
- 4.6. Repetitive sentences. Loops
- 4.7. Returning to functions
- 4.8. Arguments passed to a shell script.
- 4.9. Interaction with the user.
- 4.10. Using bash as a calculator
- 4.11. The expr command
- 4.12. What is the exit command and exit status?
- 4.13. File comparisons.
- 4.14. Comparisons of integers.
- 4.15. The shift command.
- 4.16. The let command and the arithmetic operators.
- 4.17. Logical operators.
- 4.18. The generation of random numbers.
- 4.20. C-style variables.
- 4.21. Menus in shell scripts.
- 4.22. Length of a string.
- 4.23. Finding out the numerical position of a substring in a string.
- 4.24. Extraction of a substring.
- 4.25. Deleting a substring.
- 4.26. Replacing a substring.
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5. NETWORKING
4.3. Variables in bash
A variable is a container where information can be stored. The variables are stored in memory and can be used in shell scripts to save the name of the user who executed it, the current date, the name of a directory, etc.
Let’s look at an example of a variable in a shell script:
#!/bin/bash
DATE=`date +%d-%m-%y`
echo $DATE
In the DATE variable I store the result of executing the command date +%d-%m-%y. For this I use the accent symbol «`» at the beginning and at the end of the command to delimit it. To create this symbol press the accent key and give it a blank space. That’s how that symbol appears.
Have you noticed?
That when I assign a value to the variable I do not put the $ symbol in front of it and when I use it I do.
When I run this script in my terminal I get the following:
$ ./script.sh
03-21-14
We can use scripts to store more information such as:
USER=user
In this case in the USER variable we will store the word user.
Let’s look at a more complete example in which a backup of the home directory of a specific user is made:
#!/bin/bash
DATE=`date +%d-%m-%y`
USER=user
echo ‘Starting backup…’
tar cvzf /tmp/$USER-$DATE.tgz /home/user
echo ‘Backup finished’
As you can see in the DATE and USER variables we are going to save information that will later be used in the tar command to perform the backup.
Remember.
In shell script you have to be careful with upper and lower case. DATE and date are different shell script variables. For example, get used to writing variables in capital letters and you won’t have problems.
Proposed exercise.
Modify the previous example so that it backups a test directory that you create for this purpose. Try backing up the directory, deleting it, and restoring it to check that your script is working correctly.