IT 244: Introduction to Linux/Unix

IT 244: Introduction to Linux/Unix
Class 18 Exercise

Look at the processes currently running

    ps -f

The -f option to ps gives you more information about running processes.

UID	The username of the account that started the process
PID	The process ID
PPID	The process ID of the parent process
STIME	When the process started
CMD	The command line that started the process

Run a job along with ps
```
    sleep 120 & ps -f
```
Notice that the process ID of the parent process that called sleep and ps -f is the process ID of your shell.

Run pstree while several sleep processes are running
```
    sleep 20 & sleep 20 & pstree -ph
```
Look at the bold line of processes, which denotes your shell. You will notice sleep processes running under your bash shell.

Copy print_positionals.sh to your current directory

    cp ~tsoro/course_files/it244_files/print_positionals.sh .

Look at the contents of this script
```
    cat print_positionals.sh
```
The script simply prints the first four tokens on the command line.
Run print_positionals.sh with three arguments
```
    ./print_positionals.sh foo bar bletch
```
Notice that the first positional parameter printed, 0, is the name of the command.

Copy print_arg_numbers.sh to your current directory

    cp ~tsoro/course_files/it244_files/print_arg_numbers.sh .

Look at the contents of this script
```
    cat print_arg_numbers.sh
```
Run this script with some arguments
```
    ./print_arg_numbers.sh foo bar bletch
```
The script prints the number of arguments given to it on the command line.

Set a local variable>
```
    city=Boston
```
Display the value of this variable
```
    echo $city
```
Set the variable to a value that contains a space
```
    city='New York'
```
Display the value of this variable
```
    echo $city
```
Use this value to create new variable value using single quotes
```
    big_apple='$city $city'
```
Display the value of this variable
```
    echo $big_apple
```
Single quotes do not allow you to get the value of a variable.
Try this again using double quotes
```
    big_apple="$city $city"
```
Display the value of this variable
```
    echo $big_apple
```
This time it works, because you can use the value of a variable inside double quotes.

Create the variable team
```
    team=Patriots
```
Display the value of team
```
    echo $team
```
Change the value of team
```
    team="Red Sox"
```
Display the value of team
```
    echo $team
```
Make team read only
```
    declare -r team
```
Try to change the value of team
```
    team=Celtics
```
You can't change the value because team is now read only.

Go back to your ex18 directory
```
    cd  ~/it244/ex/ex18
```
Create the script ex18.sh
```
    nano  ex18.sh
```
Write into this file commands from the sections above

Include Unix commands from the section Running Processes, up to and including the section Making a Variable Read Only.
Save this file

Save and quit.
Make this scipt executable
```
    chmod 755 ex18.sh
```
Run this script looking for error messages
```
    bash  ex18.sh > /dev/null
```
Test you script
```
    ~tsoro/it244_test/ex18.sh
```
When the script asks if you are ready for more, hit Return or Enter.
Let me check your script