CST8177 - Linux II
Midterm Solution 
more shell 
Todd Kelley 
kelleyt@algonquincollege.com 

CST8207 - Todd Kelley 
1 






.midterm solution 

.debugging shell scripts 

.exit 

.case 

.is stdin a terminal? 

.the command that does nothing 

.integer arithmetic      


 
     

2 
Today's Topics





.-v option for bash/sh 

.sh -v myscript 

.shell will print each line as its read 

.loop statements are printed once 



 
.-x option for bash/sh 

.sh -x myscript 

.shell will display $PS4 prompt and the expanded command before executing it 

.each loop iteration is shown individually   




Debugging shell scripts
CST8177 - Todd Kelley 

3 





.exit causes the shell to exit with the exit status of the last command that was run 

.exit N causes the shell to exit with exit status N  



exit command
CST8177 - Todd Kelley 
4 






case test-string in 
    pattern-1) 
        command1 
        command2 
        ;; 
    pattern-2) 
        command3 
        command4 
        ;; 
    *) 
        command5 
        ;; 
esac 

case statement
CST8177 - Todd Kelley 

5 





.the patterns are globbing patterns matched to the test-string 

.So we tend to use the * pattern as a catchall, if all other matches fail, but that's not required 

.case statement exit status is the exit status of the last command in the matching block, or 0 if no blocks match  



case statement continued
CST8177 - Todd Kelley 
6 






.We can use the vertical bar to specify alternative patterns: 


case "$character" in 
    a|A) 
        echo "The character is A" 
        ;; 
    [bB]) 
        echo "the character is B" 
        ;; 
    *) 
        echo "The character is not A or B" 
        ;; 
esac 

case statement continued
CST8177 - Todd Kelley 

7 





.A script can test whether or not standard input is a terminal 


 
[ -t 0 ] 
 
.What about standard output, and standard error? 



Is stdin a terminal?
CST8177 - Todd Kelley 
8 






.Occasionally you'll see a command called : 

.: arguments 

.That command expands its arguments and does nothing with them, resulting in a 0 exit status 



The command that does nothing
CST8177 - Todd Kelley 

9 





.examples of using expr command: 


a=`expr 3 + 4` 
a=`expr 3 - 4` 
a=`expr 3 * 4` 
a=`expr 13 / 5`  # integer division: 2 
a=`expr 13 % 5`  # remainder: 3 
.increment the integer in variable a 


a=`expr $a + 1` 

Doing integer arithmetic
CST8177 - Todd Kelley 
10