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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
4.5 Conditional sentences
Imagine that you are selling movie tickets. If someone comes to you speaking in Spanish you answer them in Spanish and if they talk to you in another language you answer them in English because imagine that it is the only language you know besides Spanish.
That translated into shell script commands would be something like the following:
if [speaking_in_Spanish]; then
I answer_in_Spanish
else
I answer_in_english
fi
Actually answer_in_Spanish and answer_in_English do not exist in shell script but instead of what I have invented we could ask for the value of some variable or ask if any variable has any value or is null, etc.
In shell script there are three different types of conditional statements:
Conditionals:
- if expression then statement
- if expression then statement1 else statement2
- if expression then statement1 else if expression2 then statement2 else statement3
Let’s see below some examples of conditional statements in shell script:
#!/bin/bash
# This is an example of if expression then statement
if [ “alboran” = “alboran” ]; then
echo “True, alboran == alboran”
fi
This is another example but using the pattern if expression then statement1 else statement2
#!/bin/bash
if [ “alboran” = “alboran” ]; then
echo “True, alboran == alboran”
else
echo “It was false”
fi
Remember.
Be careful with white spaces. Try to respect the white spaces in the expressions because otherwise when executing your shell script you may have problems.
Let’s see another example now using variables and conditional statements:
#!/bin/bash
T1=”sea of”
T2=”dawn”
if [ $T1 = $T2 ]; then
echo “True, ” $T1 ” == ” $T2
else
echo “Not true”
fi
Suggested exercises.
- Copy and execute the previous exercise. Check that it works and modify it so that T1 is equal to T2. Check now that it says “True…”.
- Create a new shell script that says whether the user running it is root or not (remember that with the “echo $USER” command I can know the name of the current user).