README.md

0x03. Shell, init files, variables and expansions

Learning Objectives in this project:

General

• What happens when you type $ ls -l *.txt.

Shell Initialization Files

• What are the /etc/profile file and the /etc/profile.d directory.
• What is the ~/.bashrc file.

Variables

• What is the difference between a local and global variable.
• What is a reserved variable.
• How to create, update and delete shell variables.
• What are the roles of the following reserved variables: HOME, PATH, PS1.
• What are special parameters.
• What is the special parameter $??

Expansions

• What is expansion and how to use it.
• What is the difference between single and double quotes and how to use them properly.
• How to do command substitution with $() and backticks.

Shell Arithmetic

• How to perform arithmetic operations with the shell.

The alias Command

• How to create an alias
• How to list aliases
• How to temporarily disable an alias.

Tasks

• 0.

  • 0-alias: Bash script that creates an alias. - Name: ls - Value: rm *

• 1. Hello you

  • 1-hello_you: Bash script that prints hello user, where is the current Linux user.

• 2. The path to success is to take massive, determined action

  • 2-path: Bash script that adds /action to the PATH. /action should be the last directory the shell looks into when looking for a program.

• 3. If the path be beautiful, let us not ask where it leads

  • 3-paths: Bash script that counts the number of directories in the PATH.

• 4. Global variables

  • 4-global_variables: Bash script that lists environment variables.

• 5. Local variables

  • 5-local_variables: Bash script that lists all local variables and environment variables, and functions.

• 6. Local variable

  • 6-create_local_variable: Bash script that creates a new local variable. - Name: BEST - Value: School

• 7. Global variable

  • 7-create_global_variable: Bash script that creates a new global variable. - Name: BEST - Value: School

• 8. Every addition to true knowledge is an addition to human power

  • 8-true_knowledge: Bash script that prints the result of the addition of 128 with the value stored in the environmental variable TRUEKNOWLEDGE, followed by a new line.

• 9. Divide and rule

  • 9-divide_and_rule: Bash script that prints the result of POWER divided by DIVIDE, followed by a new line. - POWER and DIVIDE are environment variables

• 10. Love is anterior to life, posterior to death, initial of creation, and the exponent of breath

  • 10-love_exponent_breath: Bash script that displays the result of BREATH to the power LOVE - BREATH and LOVE are environment variables - The script should display the result, followed by a new line

• 11. There are 10 types of people in the world -- Those who understand binary, and those who don't

  • 11-binary_to_decimal: Bash script that converts a number from base 2 to base 10. - The base 2 number will be stored in the environment variable BINARY. - The script should display the number in base 10, followed by a new line.

• 12. Combination

  • 12-combinations: Bash script that prints all possible combinations of two letters, except oo. - Letters are lower case, from a to z - One combination per line - The output should be alpha ordered, starting with aa - Do not print oo - Your script file should contain maximum 64 characters

• 13. Floats

  • 13-print_float: Bash script that prints a number with two decimal places, followed by a new line. - Number will be stored in environmental variable NUM

• 14. Decimal to Hexadecimal

  • 100-decimal_to_hexadecimal: Bash script that converts a number from base 10 to base 16. - The number in base 10 is stored in the environmental variable DECIMAL - The script should display the number in base 16, followed by a new line

• 15. Everyone is a proponent of strong encryption

  • 101-rot13: Bash script that encodes and decodes text using the rot13 encryption. Assume ASCII.

• 16. The eggs of the brood need to be an odd number

  • 102-odd: Bash script that prints every other line from the input, starting with the first line.

• 17. I'm an instant star. Just add water and stir.

  • 103-water_and_stir: Bash script that adds the two numbers stored in the environment variables WATER and STIR and prints the result. - WATER is base water - STIR is in base stir - The result should be in base bestchol