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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
4.12. What is the exit command and exit status?
We have already seen in previous exercises how to use the exit command to exit a script automatically.
Just as we can do with shell scripts, every command, when executed, returns an exit status also called return status or exit status. A command executed successfully, for example, returns a value of 0, while a command that has failed will show a value other than 0 (error code), which is generally a number between 0 and 255. To view the exit status of a command just show the variable $?.
Let’s see this with a practical example. This is the result of running several commands in a terminal:
As you can see, the exit status of a command with a normal response is 0 and that of a non-existent command gives a value of 127.
Let’s imagine we have the following shell script:
#!/bin/bash
echo hello
exit 48
If I run it in a terminal I will get the following result:
$ ./miniscript.sh
hello
$echo$?
48
This is because the script’s exit 48 command forces the script’s exit status to be 48. Generally an exit status other than 0 indicates any type of problem or error. If you use exit status in your scripts, always keep this in mind.
Suggested exercises:
1 Create a script that returns a value of 0 if at least one parameter is entered and 1 otherwise.
2 Run a second script to check the exit status of the first script.