Hoofdstuk 9 meerkeuze

Question 1

The echo command:

Is used for variable assignment
Duplicates the input stream to the output stream
Is used to output text to the console
Tests a variable for duplication
Copies variables from one to another

Answer 1

Is used to output text to the console

Question 2

A file begins with #!/bin/csh. This means:

Nothing, this is a comment
C Shell compatibility mode is enabled
The operator should not be using /bin/csh
Running the script will invoke /bin/csh to interpret the rest of the file
This is a Perl script

Answer 2

Running the script will invoke /bin/csh to interpret the rest of the file

Question 3

Which are appropriate editors for writing shell scripts?
(choose two)

    /bin/bash
    vi
    LibreOffice Writer
    Firefox
    nano

Answer 3

vi

nano

Question 4

Most of nano’s commands take the form of:

    Control and another character
    Alt and another character
    Mouse clicks
    The F1 through F12 function keys
    Escape followed by another character

Answer 4

Control and another character

Question 5

What does this shell script do?
FOO=/tmp/foo
if [ ! –d $FOO ]; then
mkdir $FOO
fi

Creates /tmp/foo if it does not exist
Makes the /tmp/foo directory if a file by that name exists
Outputs a message to the screen
Creates /tmp/foo and raises an error if there is a problem
Nothing, since there is a problem with the conditions in the if statement

Answer 5

Creates /tmp/foo if it does not exist

Question 6

Which of the following are correct about for and while loops?
(choose two)

for loops operate over a fixed list of items
while loops operate over a fix list of items
for loops have a test each cycle to determine if it should run again
while loops have a test each cycle to determine if it should run again
for loops require a variable over which to iterate

Answer 6

for loops operate over a fixed list of items

while loops have a test each cycle to determine if it should run again

Question 7

Given the following part of a script:
if [ -f $1 ]; then
echo “I am here”
fi

What is the meaning of $1?
It is a special variable that indicates the exit code of the command before it
It is the first argument passed to the script
It is a file called $1
It is a parameter to –f, indicating the size of the file
It is a list of files that gets interpolated

Answer 7

It is the first argument passed to the script

Question 8

Given the following script that is run through ./test.sh hello goodbye
if [ -f $2 ]; then
echo “I am here”
fi

When will “I am here” be printed?
If there are two files in the current directory
The script will always print “I am here”
Never
If a file called “hello” exists in the current directory
If a file called “goodbye” exists in the current directory

Answer 8

If a file called “goodbye” exists in the current directory

Question 9

What is the correct way to assign the word “Hello” to a variable?

    $A=”Hello”
    echo “Hello” > A
    A=”Hello”
    echo $A “Hello”
    A = “Hello”

Answer 9

A=”Hello”

Question 10

What is the correct way to save the current directory to a variable?

    A=`pwd`
    A=pwd
    A=cwd
    pwd $A
    pwd | $A

Answer 10

A=pwd

Question 11

Which shell command accepts input from the user’s keyboard?

    echo
    $1
    read
    input
    gets

Answer 11

read

Question 12

What information is held inside $? ?

    The current process id
    The number of arguments passed to the script
    The current user ID
    The previous command’s exit code
    The name of the command run

Answer 12

The previous command’s exit code

Question 13

How would you finish your script with an exit code of 42?

    return 42
    $?=42
    CODE=42
    exit 42
    break 42

Answer 13

exit 42

Question 14

The if command looks for what exit code to consider a condition to be true?

    10
    255
    0
    1
    8

Answer 14

0

Question 15

The number of users logged in is in a variable called USERS. How would you test to see if 5 users are logged in?

    test –f USERS=5
    test $USERS = 5
    test $USERS,5
    test $USERS –eq 5
    test $USERS –a 5

Answer 15

test $USERS –eq 5

Question 16

Given the following script:
while [ ! –f /tmp/foo ]; do
echo –n “.”
process_data > /tmp/foo
done
Which of the following are true?
(choose two)

If a file called /tmp/foo exists, process_data won’t be run
The screen will fill with dots.
/tmp/foo will be removed if it exists
process_data will never be run
process_data will be called at most once

Answer 16

If a file called /tmp/foo exists, process_data won’t be run

process_data will be called at most once

Question 17

A conditional that lets you make multiple comparisons with a pattern is called:

    case
    fanout
    if
    test
    branch

Answer 17

case

Question 18

What is the meaning of $(( $i + 1)) ?

1 will be added to the i variable
This will return the value of the next argument to the script
This runs the command stored in variable i
If i is 0, the loop will stop
This will return the value of the first argument to the script

Answer 18

1 will be added to the i variable

Question 19

How would you write a test that says “if /tmp/foo is a directory or USERS is greater than 5”?

    test –d /tmp/foo | $USERS > 5
    test –f /tmp/foo –o $USERS –ge 5
    test –d /tmp/foo –o $USERS –gt 5
    test /tmp/foo || $USERS > 5
    test /tmp/foo –d –o $USERS -gt 5

Answer 19

test –d /tmp/foo –o $USERS –gt 5