Debian Linux

Part I: Shell and Environment variables Shell variables are a set of name/value pairs that are available in your shell. You can set a variable by typing in a terminal =. You can use the command echo $var_name to check a variable value (attention to the $ before the variable name). If a shell variables is exported, it means the value is also accessible to child processes in the system (another shell). The exported variables are called environment variables. A few variables for you to check: USER, DESKTOP_SESSION, HOME, PWD, OLDPWD, PATH Related commands: export = echo $variable_name printenv variable_name For the hands-on practice, use ; to execute multiple commands in single command line. You will need the record of commands and output for the lab report. 1. Use the command date to print the current date of your system. 2. Change your timezone by setting the environment variable TZ to America/Regina and print the date again. 3. Change your timezone again to America/Montreal. Print the date again. 4. Print the value of the variable PS1. Read the section PROMPTING of the bash manual and try to understand what the escape characters mean. 5. Change your prompt to use a few of the available options for the PS1 variable. Research online for hints on how to setup a custom prompt for your taste. 6. Take a screenshot of the resulting prompt. 7. Change the values of the variables PWD and OLDPWD, and describe how they affect the commands pwd and cd -.

Part II: File system practice 1. Create the directory /tmp/420-321-F20/lab4 and enter this directory. 2. Create a file name sample.txt using touch. Run the command stat on the file. 3. Use touch again on the same file with no arguments, and run stat to observe what changes. 4. Touch the same file again, now with the option -a, then run stat. Explain what changes. 5. Touch again, now with the option -m, then run stat. Explain what changes. 6. List the file attributes (long list option of ls). 7. Use chmod to remove all permissions related to the file (read, write and execute). 8. Add permission to read and write only to the file owner and group. 9. Add execution permission only for the owner, using both methods (letters and numbers). 10. Use a wildcard to list all files that end with .txt files in the current directory. Part III: Connecting shell commands In a shell, you can use special characters to connect commands (|), send the output of a command to a file (>), perform multiple tasks in sequence (;), and expand the result of commands or arithmetic expressions. 1. Print the string date and send the output to the file lab4.sh. 2. Print the string echo Running my lab#4 script and append to lab4.sh. 3. Change the permission of this new file, in a way that only the owner of the file can read, write and execute it. 4. Execute the file with ./lab4.sh. 5. Create a hardlink named hard.sh and a symbolic link named soft.sh, both pointing to the same file lab4.sh. 6. Use a shell command to show that the files lab4.sh and their links have the same content. 7. Execute all your script files and tell if there is any difference in their output. 8. List the content of the directory with ls -l. Note the number that appear just after the permissions of each file. That is the number of hard links pointing to a physical location (inode). Note also the file types, the first character that appears, just before the permission of each file. 9. Remove the file lab4.sh and list the directory content with ls -l again. 10. Describe the changes you see from the previous run of ls. 11. Restore the file lab4.sh by creating a hard link from hard to lab4.sh 12. Add the line sleep 3 at the end of lab4.sh.

13. Run all your files again, and explain if there is any difference in the output. 14. Create a new user john. 15. Use su john to change user and try to execute lab4.sh as john. 16. Go back to your user, and change the file permissions in a way that john will be able to execute the script. 17. Add a line to the script to use another command or environment variable that will identify the user running the script. 18. Run the script and record the output. 19. Use brace expansion to create files file1.txt, file2.txt and fie3.txt in a single command. 20. Combine the commands cat and grep to catch all occurrences of the string date in the current directory. 21. Combine the previous command with wc to count how many occurrences there are. 22. Combine the commands ls and wc to count how many files that end with .txt 23. Use the command echo with command expansion to print how many files there are in the current directory. 24. Adapt the previous command, to count how many scripts you have in this directory. Part IV: Recording commands This time youll collect the list of commands yourself. Each new command practiced this week should be included in your ever-growing commands table. Youll be asked to include the updated table with all commands description in the next lab report.