Chapter 8, Lab 1: Writing and Executing a Shell Script (20 Minutes)

Learning Objectives and Outcomes

In this lab you will learn to write and execute a shell script that includes comments. You will use chmod to make the file that holds the script executable and include a line that starts with #! in the script to make sure bash executes it. This lab also provides an introduction to positional parameters.

Reading Read Writing and Executing a Simple Shell Script on pages 294299 of Sobell. Procedure 1. Use vim or cat (see page 20 of this lab manual for instructions) to create a file named short with the following line in it: echo 'hi there'

2. Use cat to verify the contents of short and then try to execute it. Use ls l to display the permissions for short. Read the tip on Sobell, page 296. 3. Use chmod (Sobell, pages 100 and 295) to make the file executable, display the permissions for short, and try executing the file again.

4. Add a line that starts with #! (Sobell, page 297) to the beginning of short to make sure it is executed by bash.

5. Add a comment line (Sobell, page 298) to short that explains what the script does.

6. Within a shell script, the shell expands $1 (a variable called a positional parameter; Sobell, page 475) to the first argument on the command line the script was called with. Write and execute a script named first that displays (sends to standard output) the first argument on the command line it was called with. Include the #! line and a comment. Remember to make the file executable.

7. Write a shell script that copies the file named by its first argument to a file with the same name with the filename extension of .bak. Thus, if you call the script with the argument first (and a file named first exists in the working directory), after the script runs you would have two files: first and first.bak. Demonstrate that the script works properly.

8. Read the caution titled Always quote positional parameters on page 475 of Sobell. Use touch to create a file whose name has a SPACE in it. What happens when you give that filename as an argument to cptobak from the previous step? Modify the cptobak script from the previous step by quoting the positional parameters in the cp line. Now what happens when you use the script to make a copy of a file with a SPACE in its name?

Deliverables This lab gives you practice writing and executing shell scripts.

Chapter 8, Lab 2: Shell Parameters and Variables (15 Minutes)

Learning Objectives and Outcomes

In this lab you will learn about user-created variables and keyword variables.

Reading Read Parameters and Variables on page 310 of Sobell up to Pathname expansion in assignments on page 313.

Procedure

Although variables are mostly used in scripts and read by programs, you can experiment with them on the command line.

1. Assign your name to the variable named myname and use echo to display the value of myname when it is unquoted, quoted using double quotation marks, and quoted using single quotation marks. (Refer to Parameter substitution on page 312 of Sobell and Quoting the $ on page 312 of Sobell.)

2. Use the readonly (Sobell, page 315) builtin to make the myname variable you created in the previous step a readonly variable and then assign a new value to it. What happens?

3. What is the value of your HOME (Sobell, page 317) keyword variable? Demonstrate that the tilde (~; Sobell, page 317) holds the same value as HOME. List the contents of your home directory using a tilde.

4. The PATH (Sobell, page 318) keyword variable specifies the directories in the order bash should search them when it searches for a script or program you run from the command line. What is the value of your PATH variable? Append the absolute pathname of the bin directory that is a subdirectory of your home directory to the PATH variable. What does this change allow you to do more easily? 5. The PS1 (Sobell, page 319) keyword variable holds the value of your primary shell prompt. Change the value of this variable so that your prompt is simply a $ followed by a SPACE when you are working as yourself and a # followed by a SPACE when you are working with root privileges.

6. The date (Sobell, page 62) utility displays the date and time. Write and execute a shell script that displays the date and time, the name of your home directory, and the value of your PATH variable.

Deliverables This lab gives you practice working with user-created variables and the HOME