IT 244: Introduction to Linux/Unix - Class 24 Exercise

IT 244: Introduction to Linux/Unix
Class 24 Exercise

Log in to pe15.cs.umb.edu

Run the ssh client

Connect to pe15.cs.umb.edu.

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
```

Simple `for` Loop

Using your favorite editor, create the script for_1.sh

Make this script executable
```
chmod 755 for_1.sh
```
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

Using your favorite editor, create the script for_2.sh
Notice that here the list created by the expansion of ~/* is written in the script itself, and is not taken from the command line.

Make this script executable
```
chmod 755 for_2.sh
```
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

Using your favorite editor, create the script for_3.sh

Make this script executable
```
chmod 755 for_3.sh
```
Run this script
```
./for_3.sh
```
You should see
```
0
1
2
3
4
```

`while` Loops

Using your favorite editor, create the script count_to_five.sh

Make this script executable
```
chmod 755 count_to_five.sh
```
Run this script
```
./count_to_five.sh
```
You should see
```
1
2
3
4
5
```

Practice using the debugging feature

Run count_to_five.sh using the debugging feature
```
bash -x count_to_five.sh
```
Notice that each line of code is printed as it is executed, with the current value of the variable substituted for the variable name.

`until` Loop

Using your favorite editor, create the script count_until.sh
Notice that this script uses the -gt, greater than, option, as opposed to the -lt, less than, option employed in the while loop script above.

Make this script executable
```
chmod 755 count_until.sh
```
Run this script
```
./count_until.sh 10
```
You should see
```
1
2
3
4
5
6
7
8
9
10
```

`continue`

Using nano, or your favorite editor, create the script continue.sh

Make this script executable
```
chmod 755 continue.sh
```
Run the script continue.sh
```
./continue.sh
```
You should see
```
Adding 1 to 0
Adding 3 to 1
Adding 5 to 4
Adding 7 to 9
Adding 9 to 16
Adding 10 to 25

total: 35
```
Notice that the echo command is not run for the values of 2, 4, 6 and 8.

Instead, the loop progresses to the next value of the loop variable.

`break`

Using nano, or your favorite editor, create the script break.sh

Make this script executable
```
chmod 755 break.sh
```
Create two dummy files
```
touch 1 1.sh
```
Make the dummy file 1.sh executable
```
chmod 755 1.sh
```
Run the script break.sh
```
./break.sh
```
You should see
```
First executable file: 1.sh
```