IT 244: Introduction to Linux/Unix - Class 24 Exercise, Tuesday, May 5th

IT 244: Introduction to Linux/Unix
Class 24 Exercise, Tuesday, May 5th

Log in to users

Log in to a Windows machine or your own laptop

Enter your Unix username as the account name. Then enter your password.

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 ex24 directory
    mkdir  ex24
Go to your ex24 directory
    cd  ex24
Start Up a script Session

Execute the script command, using the --flush option
    script --flush
Using test, as [ ] , with Numbers
Use test with the -eq (equality for numbers) operator
    [ 4 -eq 5 ] ; echo $?
Since anything other than 0 as an exit status signals failure, this means that the equality test has failed.

Be sure to use a space before and after each [ and ] character.
Use the -eq operator with the same number on both sides
    [ 4 -eq 4 ] ; echo $?
Since 0 means success, this means that the expression evaluated to true.
Use test with the -ne (not equal for numbers) operator
    [ 4 -ne 5 ] ; echo $?
0 means true.
Use -ne again
    [ 4 -ne 4 ]; echo $?
1 means false.
Use test with the -gt (greater than) operator
    [ 4 -gt 5 ] ; echo $?
    [ 5 -gt 4 ] ; echo $?
Use the -ge (greater than or equal to) operator
    [ 5 -ge 4 ] ; echo $?
    [ 5 -ge 5 ] ; echo $?
    [ 4 -ge 5 ] ; echo $?
Use the -lt (less than operator)
    [ 4 -lt 5 ] ; echo $?
    [ 5 -lt 4 ] ; echo $?
Use the -le (less than or equal to) operator
    [ 4 -le 5 ] ; echo $?
    [ 4 -le 4 ] ; echo $?
    [ 5 -le 4 ] ; echo $?
Using test with String Comparison Operators
Use test with the = (string equality) comparison operator
    [ "foo" = "foo" ] ; echo $?
    [ "foo" = "bar" ] ; echo $?
Use test with the != (string not equal) comparison operator
    [ "foo" != "bar" ] ; echo $?
    [ "foo" != "foo" ] ; echo $?
Using test with Single String Operators
Use test with the -n (length greater than 0) string operator
    [ -n "foo" ] ; echo $?
    [ -n "" ] ; echo $?
Use test with the -z (length is 0) string operator
    [ -z "" ] ; echo $?
    [ -z "foo" ] ; echo $?
Using test logical operators
Use test with the -a (logical AND) operator
    [ 5 -lt 6 -a "foo" != "bar" ]; echo $?
    [ 5 -lt 6 -a "foo" != "foo" ]; echo $?
Use test with the -o (logical OR) operator
    [ 5 -lt 6 -o "foo" != "foo" ]; echo $?
    [ 5 -lt 5 -o "foo" != "foo" ]; echo $?
Use test with the ! (logical NOT) operator
    [ ! 5 -lt 5 -o "foo" != "foo" ]; echo $?
    [ ! 5 -lt 6 -o "foo" != "foo" ]; echo $?
Using test with File and Directory Operators
Create the empty file empty.txt
    touch empty.txt
Make empty.txt read only
    chmod 444 empty.txt
Create the file foo.txt
    cat > foo.txt [Enter]
    foo [Enter]
    Control d
Make sure this file is not empty
    cat foo.txt
Give yourself full privileges to this file
    chmod 700 foo.txt
Create the directory dir1
    mkdir dir1
Use test with the -d (is it a directory) operator
    [ -d dir1 ]; echo $?
    [ -d foo.txt ]; echo $?
Use test with the -e (it exists) operator
    [ -e foo.txt ]; echo $?
    [ -e bar.txt ]; echo $?
Use test with the -f (is an ordinary file) operator
    [ -f foo.txt ]; echo $?
    [ -f dir1 ]; echo $?
Use test with the -r (exists and is readable) operator
 
    [ -r empty.txt ]; echo $?
    [ -r xxxx.txt ]; echo $?
Use test with the -s (exists and has a size greater than 0) operator
    [ -s foo.txt ]; echo $?
    [ -s empty.txt ]; echo $?
Use test with the -w (exists and is writeable) operator
    [ -w foo.txt ]; echo $?
    [ -w empty.txt ]; echo $?
Use test with the -x (exists and is executable) operator
    [ -x foo.txt ]; echo $?
    [ -x empty.txt ]; echo $?
if ... then ... else ...
Open up a second login session, while leaving your first login session going.

You will use this second login session for file editing.

This is so that your use of nano does not interfere with the script session in your first session.

Make sure that you keep track of what is to be done in which login window!
In your SECOND login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your SECOND login window: Using your favorite editor create the script arg_count.sh
    #! /bin/bash
    #
    # prints the number of arguments given to this script

    if test $# -eq 0 
    then
        echo "You entered no arguments"
    else 
        echo "You entered $# arguments"
    fi
In your FIRST login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your FIRST login window: Change the permissions on arg_count.sh to make it executable
    chmod 755 arg_count.sh
In your FIRST login window: Test the script several times using bash with the -x option
    bash -x arg_count.sh
    bash -x arg_count.sh foo
    bash -x arg_count.sh foo bar
    bash -x arg_count.sh foo bar bletch
if ... then ... elif ...
In your SECOND login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your SECOND login window: Using your favorite editor create the script arg_count_2.sh
    #! /bin/bash
    #
    # prints the number of arguments given to this script

    if test $# -eq 0 
    then
        echo "You entered no arguments"
    elif test $# -eq 1 
    then
        echo "You entered 1 argument"
    elif test $# -eq 2 
    then
        echo "You entered 2 arguments"
    elif test $# -gt 2
    then
        echo "You entered more than 2 arguments"
    fi
In your FIRST login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your FIRST login window: Change the permissions on arg_test.sh to make it executable
    chmod 755 arg_count_2.sh
In your FIRST login window: Test the script several times using bash with the -x option
    bash -x arg_count_2.sh
    bash -x arg_count_2.sh foo
    bash -x arg_count_2.sh foo bar
    bash -x arg_count_2.sh foo bar bletch
Simple for Loop
In your SECOND login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your SECOND login window: Using your favorite editor, create the script for_1.sh
    #! /bin/bash
    #
    # demonstrates the for ... loop
    
    for arg
    do
        echo $arg
    done
In your FIRST login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your FIRST login window: Make this script executable
    chmod 755 for_1.sh
In your FIRST login window: Run this script with an ambiguous file reference
    ./for_1.sh  ~/*
The ambiguous file reference ~/* is expanded into a list of all files in your home directory
for ... in ... Loop
In your SECOND login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your SECOND login window: Using your favorite editor, create the script for_2.sh
    #! /bin/bash
    #
    # demonstrates the for ... in ... loop
    
    for arg in ~/*
    do
        echo $arg
    done
Notice that here the list created by the expansion of ~/* is written in the script itself, and is not taken from the command line.
In your FIRST login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your FIRST login window: Make this script executable
    chmod 755 for_2.sh
In your FIRST login window: Run this script without arguments
    ./for_2.sh
You get the same results as with for_1.sh.

But here the arguments come expanding the ambigous file reference inside the script itself.
Three Expression for Loop
In your SECOND login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your SECOND login window: Using your favorite editor, create the script for_3.sh
    #! /bin/bash
    #
    # demonstrates the three expression for loop
    
    for (( count=0; count<20; count++ ))
    do
        echo $count
    done
In your FIRST login window: Make sure you are in your ex24 directory
    cd ~/it244/ex/ex24
In your FIRST login window: Make this script executable
    chmod 755 for_3.sh
In your FIRST login window: Run this script
    ./for_3.sh
Exit Your script Session

Use the exit command
    exit
You should see a confirmation message confirming that the script session is finished, resulting in a file called typescript, and you will probably also noticed that you are back in the original directory, from where you first ran the script command.