IT 244 Class Exercise 11

When finished: Remember to check with instructor to make sure you are recorded as having worked on the class exercise -- even if you have not completed it!

Log in to pe15

Run the ssh client

Use the values in the table below to connect to pe15.

ssh configuration parameter	value
protocol	ssh
ssh version	2
ssh port	22
host	pe15.cs.umb.edu
user name	your Unix username
Authentication method	password

Enter your password
A dialog box will appear on the screen into which you must type the password for your Unix account.

Directory for this Exercise

(When you are ready for me to check this exercise, please scroll back up to where you entered these commands!)

Make sure you are in your home directory
```
    cd
```
Go to your it244 directory
```
    cd  it244
```
Go to your ex directory
```
    cd  ex
```
Create an ex11 directory
```
    mkdir  ex11
```
Go to your ex11 directory
```
    cd  ex11
```

Start Up a Script Session

Execute the script command, using the --flush option

    script --flush

Combining Options

Perform a long listing of the files/directories for this course
```
    ls -l /home/ckelly/course_files/it244_files
```
Use ls to see the directory contents in reverse order by date
```
    ls -ltr /home/ckelly/course_files/it244_files
```
Here you are combining the options indicating you want a long listing (l), ordered by date and time (t), in reverse order (r).
Use ls to see the access permissions on the it244_files directory
```
    ls -ld /home/ckelly/course_files/it244_files
```
Here you are combining the options indicating you want a long listing (l) of the directory itself (d), not its contents.

The Human Readable Option

Use df to see the disk space available on pe15
```
    df
```
Notice two things.

First, the available space field is very hard to read.

Second, you are seeing disk partitions on more than one machine.

blade61 and blade66 are two different machines.

The single, logical, filesystem we see is composed of multiple physical disks and partitions.
Now use df with the -h option
```
    df -h
```
The free disk space is now much easier to read.

The --help Option

Invoke the --help option for cat
```
    cat --help
```
Look at the help for ls
```
    ls --help
```
Notice that some help is very long.
Explore the --help option for cd
```
    cd --help
```
cd does not respond to the --help option, or, for that matter, -h.

Running Commands with Pathnames or Only the Name of the Command

Run ls using only the name of the command
```
    ls  ~ckelly
```
Learn the location of the ls executable file
```
    which ls
```
Run ls using an absolute pathname
```
    /bin/ls  ~ckelly
```
This has the same effect as typing the name of the command on the command line, which is also the name of the executable file for ls.

The PATH System Variable

Display the value of PATH
```
    echo $PATH
```
Notice that each directory name is an absolute pathname separated by a colon, : .

Notice also, that the current directory, . , does not appear in this list.

Running a Program in the Current Directory

Go to the ex11 directory
```
    cd ~/it244/ex/ex11
```
Make sure you are in your ex11 directory
```
    pwd
```
Run the shell script hello.sh which is in my course_files/it244_files directory
```
    ~ckelly/course_files/it244_files/hello.sh
```

Copy hello.sh to your current directory

    cp ~ckelly/course_files/it244_files/hello.sh  .

Make sure the copy operation worked
```
    ls
```
Try to run the program you just copied using just the name of the file
```
    hello.sh
```
You get an error message.
Run the program by placing ./ in front of the file name
```
    ./hello.sh
```
Now the program run.

Exit Status

Run ls with no options or arguments
```
    ls
```
Examine the exit status returned by the last command
```
    echo $?
```
Since ls ran without any problems, it returned an exit status of 0, indicating that all went well.
Now run ls on a file that doesn't exist
```
    ls foobar
```
Examine the exit status returned by the last command
```
    echo $?
```
Since ls failed, it returns a non-zero exit status.
See what this exit status means
```
    ls --help | tail
```
Returning the value 2 means ls ran into a serious problem.

Exit Your Script Session

Use the exit command

    exit

You should see a confirmation message confirming that the script is finished, resulting in a file called typescript

Bash Script for this Exercise

Go to your ex11 directory
```
    cd ~/it244/ex/ex11
```
Create the script ex11.sh
```
    nano  ex11.sh
```
Write into this file the commands you used above

Include Unix commands from the section Combining Options to the section Exit Status.
Save this file

Save and quit.
Make this script executable
```
    chmod  755  ex11.sh
```
Run the script
```
    ./ex11.sh
```
Fix any errors you find.

If you have trouble, see me.

When finished:

Remember to check with instructor to make sure you are recorded as having completed the class exercise.
When you are ready, be prepared to show me:
- Your command line interaction -- in other words, scrolling up in the terminal windows, not just running the history command!
- Any other deliverables specified in the instructions, such as scripts or other files.