IT 244: Introduction to Linux/Unix - Class 26 Exercise, Wednesday, December 11th

IT 244: Introduction to Linux/Unix
Class 26 Exercise, Wednesday, December 11th

Log in to users

Run the ssh client

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

ssh configuration parameter	value
protocol	ssh
ssh version	2
ssh port	22
host	users.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

Go to your ex directory
```
    cd  ~/it244/ex
```
Create an ex26 directory
```
    mkdir  ex26
```
Go to your ex26 directory
```
    cd  ex26
```

Here Document

Using nano, or an editor of your choice, create here.sh

    #! /bin/bash
    #
    # demonstrates how here documents work
    
    echo -n "Here is the information you requested: "
    grep $1 <<EOF
    Boston Red Sox 
    New York Yankees
    Toronto Blue Jays
    Baltimore Orioles
    Tampa Bay Rays
    EOF

Make this script executable
```
    chmod 755 here.sh
```

Run this script a couple of times

    ./here.sh Boston
    ./here.sh Rays
    ./here.sh Orio

Braces with Variables

Define the variable foo
```
    foo=FOO
```
Display the value of foo
```
    echo $foo
```
Use foo with a period
```
    echo $foo.bar
```
Use foo with a slash
```
    echo $foo/bar
```
Use foo concatenated with another string
```
    echo $foobar
```
bash does not see the variable foo followed by the string "bar".

It sees a new variable, foobar.
Use foo concatenated with another string, but using braces
```
    echo ${foo}bar
```

Special Parameters

Look at the running processes
```
    ps
```
Use the $$ special parameter
```
    echo $$
```
The value returned by $$ is the process ID of your current shell.
Run a command that succeeds
```
    ls
```
Use the $? special parameter
```
    echo $?
```
The command returns 0 since the previous command executed successfully.
Run a command that fails
```
    ls xxxxx
```
Use the $? special parameter
```
    echo $?
```
The command returns 2 indicating that the previous command failed.
Run a command in the background
```
    sleep 120 &
```
Use the $! special parameter
```
    echo $!
```
The number returned is the same as the PID that appeared on the command line when the background job was created.

Positional Parameters

Using nano or an editor of your choice, create the script positionals.sh

    #! /bin/bash
    #
    # prints the values of the various positional parameters
    
    echo "This shell script was called using $0"
    echo "This shell script was called using $# command line arguments"
    echo "Here are the command line arguments: $@"
    echo "Positional parameter 1: $1"
    echo "Positional parameter 2: $2"
    echo "Positional parameter 3: $3"

Make this script executable
```
    chmod 755 positionals.sh
```
Run positionals.sh with some arguments
```
    ./positionals.sh foo bar bletch
```

shift

Using nano, or an editor of your choice, create the following shell script shift.sh

    #! /bin/bash
    #
    # uses shift to print the positional arguments
    
    while [ $# -gt 0 ]
    do
      echo $1
      shift
    done

Make this script executable
```
    chmod 755 shift.sh
```
Run this script with a couple of arguments
```
    ./shift.sh foo bar bletch
```
The shift command moves each command line argument in turn into the first positional parameter, allowing us to print each argument until there are no more command line arguments left.

set

Using nano, or an editor of your choice, create the following shell script set.sh

    #! /bin/bash
    #
    # uses set to create arguments
    
    echo "Here are the arguments given to this script: $*"
    set foo bar bletch
    echo "After calling set"
    index=1
    while [ $# -gt 0 ]
    do
      echo "Positional parameter $index: $1"
      shift
      (( index += 1 ))
    done

Make this script executable
```
    chmod 755 set.sh
```
Run this script with no arguments
```
    ./set.sh
```
Even though no arguments were given to the script at the command line, set created these arguments from within the script.

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.

IT 244: Introduction to Linux/Unix Class 26 Exercise, Wednesday, December 11th