Q1. Which of the three methods will copy the directory named "photo dir" recursively from the user's home directory to /backups?
cp -R "~/photo dir" /backups #method1
cp -R ~"/photo dir" /backups #method2
cp -R ~/"photo dir" /backups #method3- None of the three methods will expand to the user's home directory. Only using
"$HOME/photo dir"will be successful. - Only method 1 will expand
"~/"to the user's home directory and then append the quoted directory name that includes a space. - Only method 2 will expand
"~/"to the user's home directory and then append the quoted directory name that includes a space. - Only method 3 will expand
"~/"to the user's home directory and then append the quoted directory name that includes a space.
$ ls -1
Beach photo1.jpg
Photo1.jpg
Photo2.jpg
Script.sh
$ cat script.sh
for i in $(ls *.jpg); do
mv $i ${i}.bak
done- ls: cannot access nonexistentfile: No such file or directory
- The for loop will split on word boundaries and Beach photo1.jpg has a space in it.
- The mv command will fail because the curly bracket is a special character in Bash and cannot be used in the names of files.
- Running script.sh will be successful as the ls command builds a list of files in the current directory and for loops through that list renaming files with a .bak extension.
-
( command ) -
sh command -
{ command; } -
(( command ))
reference. Subshells are one way for a programmer to capture (usually with the intent of processing) the output from a program or script. Commands to be run inside a subshell are enclosed inside single parentheses and preceeded by a dollar sign: DIRCONTENTS=$(ls -l) echo ${DIRCONTENTS}
echo "1 2 3" | awk '{for (i=1; i<=NF; i++) s=s+$i};END {print s}'- 6
- 123
- 3
- 600
reference. AWK is a programming language that is designed for processing text-based data, either in files or data streams, or using shell pipes. In other words you can combine awk with shell scripts or directly use at a shell prompt.
Q5. The command below will search the root filesystem for files named "finance.db". In this context, what information is being sent to /dev/null?
find / -name "finance.db" 1>results.txt 2>/dev/null- the names of files that do not match finance.db
- information sent to the standard error-for example, errors that the find command displays as it runs
- the names of files that match finance.db
- information sent to the standard output-that is, the path to files the find command has located
reference. Syntax to redirect stderr (standard error) to a file: command 2> errors.txt.
-
sed -i '/^$/d' textfile -
sed '/^$/d' textfile -
cat textfile | sed '/^$/d -
sed -i 's/^$//' textfile
reference
sed : sed is a stream editor. A stream editor is used to perform basic text transformations on an input stream.
-i[SUFFIX] : This option specifies that files are to be edited in-place.
'/^$/d' : regex is between the //. ^ is the beginning of the line, $ is the end of the line. ^$ means the start and end have nothing in between.
d : Delete the pattern space; immediately start next cycle.
Warning, this example above will not work on a mac terminal due to different UNIX flavours. There is a way to make it work on a mac adding an extra flag -e, or even just -- (found on StackOverflow): sed -i -e '/^$/d' textfile.txt
awk -F: '/user1/{print $1 "-" $3 "-" $6}' /etc/passwd- It would show the username, UID, and home directory of user1 separated by colons.
- It would print the UID, GID, and home directory of user1 separated by hyphens.
- It would print the UID, comment, and home directory of user1 separated by hyphens.
- It would show the username, UID, and home directory of user1 separated by hyphens.
reference. Traditionally, the /etc/passwd file is used to keep track of every registered user that has access to a system. The /etc/passwd file is a colon-separated file that contains the following information: 1-Username, 2-Password, 3-User ID (UID), 4-Group ID (GID), 5-User ID Info (GECOS), 6-Home directory, 7-Command/shell
- It will cause Bash to exit if a function or subshell returns a nonzero status code.
- It will cause Bash to exit if a conditional returns a non-zero status code.
- It will cause Bash to exit if local, declare, or typeset assignments return a nonzero status code.
- It will cause Bash to exit if a command, list of commands, compound command, or potentially a pipeline returns a nonzero status code.
reference. The set -e option instructs bash to immediately exit if any command [1] has a non-zero exit status. You wouldn't want to set this for your command-line shell, but in a script it's massively helpful. In all widely used general-purpose programming languages, an unhandled runtime error - whether that's a thrown exception in Java, or a segmentation fault in C, or a syntax error in Python - immediately halts execution of the program; subsequent lines are not executed.
- get
- argument
- read
- input
mysql < file.sql > file.txt- a copy of the contents of file.sql
- an error indicating that this is invalid syntax
- the error output of the MySQL command
- the non-error output of the MySQL command
Note: check the question below for a variant.
mysql < file.sql > out.txt- The output on the screen will be identical to out.txt
- There will be no output on the screen as it's being redirected to out.txt.
- The output on the screen will be identical to out.txt plus line numbers.
- The out.txt file will hold STDERR and STDOUT will go to the screen.
Note: check the question above for a variant.
- When the command creates files, they will be owned by the group owner of the command.
- The SUID bit allows anyone to execute the command no matter what other permissions are set.
- When the command is executed, its running privileges elevate to the user owner of the command.
- When the command is executed, its running privileges elevate to the group owner of the command.
reference. The Linux and Unix access rights flags setuid and setgid (short for set user identity and set group identity)[1] allow users to run an executable with the file system permissions of the executable's owner or group respectively and to change behaviour in directories.
Q13. In order to extract text from the first column of file called textfile, which command would you use?
-
cat {$1,textfile} -
cat textfile | awk [print $1] -
cat textfile | awk '{print $1}' -
awk textfile {print $1}
(reverse-i-search)`':- Esc + R
- Ctrl + H
- Ctrl + R
- Alt + R
Note: On the Mac it will show bck-i-search: instead of (reverse-i-search).
-
var=$( expr 10 / 8 ) -
(( var= 10 /8 )) -
var=$(( 10 / 8 )) -
var=$(echo 'scale=2; 10 / 8' | bc)
reference. The bc command is used for command line calculator. It is similar to basic calculator by using which we can do basic mathematical calculations. The division with 2 digit precision will be passed to bc, evaluated, and assigned to the variable.
txt=Penguins
[[ $txt =~ [a-z]{8} ]]; echo $?- 0, representing 'true', because the variable "txt" contains eight letters
- 0, representing 'true', because everybody loves penguins!
- 1, representing 'false', because the variable "txt" is longer than eight characters
- 1, representing 'false', because the variable "txt" does not contain eight lowercase letters between a and z
HAL>-
SHELL="HAL\>" -
SHELL="HAL>" -
export PS1="HAL>" -
PS1="HAL\>"
VAR="/var/www/html/website.com/html/"
echo "${VAR#*/html}"-
/website.com/html/ -
/html/website.com/html/ -
/var/www/html/website.com/ - Nothing will be echoed on the screen.
reference
What is happening here quoting the POSIX shell specification: ${parameter#[word]}. Remove Smallest Prefix Pattern. The word shall be expanded to produce a pattern. The parameter expansion shall then result in parameter, with the smallest portion of the prefix matched by the pattern deleted.
For instance ${VAR#?} expands to the value of $VAR with the first character deleted. And ${VAR#\*/html}expands to include all characters to and including the/htmltext which will be deleted from the variable producing the output of/website.com/html/
Q19. If prompted for text at the standard input, you can tell the command you're done entering text with what key combination?
- Ctrl + A (Windows) or Command + A (Mac)
- Ctrl + E (Windows) or Command + E (Mac)
- Ctrl + D (Windows) or Command + D (Mac)
- Ctrl + Z (Windows) or Command + Z (Mac)
Q20. In order for a Bash script to be executed like an OS command, it should start with a shebang line. What does this look like?
-
#!/usr/bin/env bash -
~/usr/bin/env bash -
'$!/usr/bin/env bash -
#/usr/bin/env bash
The date is: Sun Mar 24 12:30:06 CST 2019!-
echo "The date is: !" -
echo "The date is: date!" -
echo "The date is: (date)!" -
echo "The date is: $(date)!"
Q22. Suppose your current working directory is your home directory. How could you run the script demo.sh that is located in your home directory? Find three correct answers.
A. /home/demo.sh
B. ./demo.sh
C. ~/demo.sh
D. bash /home/demo.sh
E. bash demo.sh- B, C, E
- A, B, C
- C, D, E
- B, D, E
-
find . -type html -
find . -name *.html -
find *.html -
find . -name \*.html -print
The second seems well, but will expand the \* if there is any .html file on your working directory.
cat < in.txt > out.txt- The output from the command line. By default STDIN comes from the keyboard.
- Nothing because you can't redirect from file (in.txt) to another file (out.txt). You can only redirect from a command to a file.
- It would be the contents of in.txt.
- Nothing. The redirect will create a new empty file but there will not be any output from the cat command to redirect.
(( $a == $b ))
echo $?- It loops between the values of
$aand$b. - It tests whether the values of variables
$aand$bare equal. - It returns
$bif it is larger than$a. - It returns
$aif it is larger than$b.
-
; ; -
: : -
done -
$$
#!/usr/bin/env bash
case $num in
1)
echo "one"
;;
2)
echo "two"
;;
*)
echo "a mystery"
;;
esac- a case that matches any value, providing a default option if nothing else catches that value
- a case only for what happens when the asterisk character is passed into the script
- the action of all of the other cases combined together
- an action that is taken for any input, even if it matches a specified condition
-
touch file{1+10}.txt -
touch file{1-10}.txt -
touch file{1..10}.txt -
touch file(1..10).txt
-
$$ -
$? -
$! -
$@
#!/bin/bash
fname=john
john=thomas
echo ${!fname}- john
- thomas
- Syntax error
- blank
-
A
-
B
-
C
-
D
Here's a text based version of Q.30:
ll
-rw-r--r-- 1 frankmolev staff 374 Jun 3 19:30 .
-rw-r--r-- 1 frankmolev staff 1666 Jun 3 19:30 ..
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 file1.txt
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 file2.txt
..
ll | sed -e 's,file,text,g'
- A
-rw-r--r-- 1 frankmolev staff 374 Jun 3 19:30 .
-rw-r--r-- 1 frankmolev staff 1666 Jun 3 19:30 ..
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 file1.file
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 file2.file
..
- B
-rw-r--r-- 1 frankmolev staff 374 Jun 3 19:30 .
-rw-r--r-- 1 frankmolev staff 1666 Jun 3 19:30 ..
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 file1.txt
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 file2.txt
..
- C
-rw-r--r-- 1 frankmolev staff 68 Jun 3 19:30 .
-rw-r--r-- 1 frankmolev staff 1666 Jun 3 19:30 ..
- D
-rw-r--r-- 1 frankmolev staff 374 Jun 3 19:30 .
-rw-r--r-- 1 frankmolev staff 1666 Jun 3 19:30 ..
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 text1.txt
-rw-r--r-- 1 frankmolev staff 0 Jun 3 19:30 text.txt
..
#!/bin/bash
read -p "Enter your pet type." PET
if [ $PET = dog ] ;then
echo "You have a dog"
fi- If the value of PET doesn't match dog, the script will return a nonzero status code.
- There is nothing wrong with it. The condition checks the value of PET perfectly.
- It will fail if the user hits the Enter (Return) key without entering a pet name when prompted.
- The then statement needs to be on a separate line.
- It just works by default.
-
history --shared -
history --combined -
shopt -s histappend
-
$@treats each quoted argument as a separate entity.$*treats the entire argument string as one entity. -
$*treats each quoted argument as a separate entity.$@treats the entire argument string as one entity. -
$*is used to count the arguments passed to a script,$@provides all arguments in one string. -
$*is the wildcard that includes all arguments with word splitting,$@holds the same data but in an array.
if [ -f file.txt ]; then
echo "file.txt exists"
fi-
/usr/bin/test -
/usr/bin/[ -
the built-in [ command -
/usr/bin/[[
#!/bin/bash
Linux=('Debian' 'Redhat' 'Ubuntu' 'Android' 'Fedora' 'Suse')
x=3
Linux=(${Linux[@]:0:$x} ${Linux[@]:$(($x + 1))})
echo "${Linux[@]}"- Debian Redhat Ubuntu Android Fedora Suse
- Android
- Fedora Suse
- Debian Redhat Ubuntu Fedora Suse
-
/etc/bash.conf -
~/.profile -
/etc/bashprofile -
~/profile
Q38. Given the listed permissions on data.txt is it possible that user2 could have read, write, and execute permissions on data.txt?
$ ls -l
total 0
-rwx------+ 1 user1 user1 0 Oct 27 10:54 data.txt- No, it's clear that user2 does not have read, write, and execute permissions.
- Yes, the
+at the end of the 10-digit permission string signifies there's an access control list. This could possibly give user2 permissions not visible byls -l. - It's possible that SELinux provides read, write, and execute permissions for user2 which are not visible with
ls -l. - Yes, the
+at the end of the 10-digit permission string signifies there's an extended attribute set. This could give user2 permissions to read, write, and execute data.txt.
#!/bin/bash
declare -A ARRAY=([user1]=bob [user2]=ted [user3]=sally)
KEYS=(${!ARRAY[@]})
for (( i=0; $i < ${#ARRAY[@]}; i+=1 ));do
echo ${KEYS[$i]} - ${ARRAY[${KEYS[$i]}]}
done- It sorts the associative array named ARRAY and stores the results in an indexed array named KEYS. It then uses this sorted array to loop through the associative array ARRAY.
- Using a C-style for loop, it loops through the associative array named ARRAY using the associative array's keys and outputs both the key and values for each item.
- It creates an indexed array of the associative array named ARRAY. It then uses a C-style for loop and the indexed array to loop through all items in the associative array, outputting the key and value of each array item using the index number.
- It creates an associative array named ARRAY, which it loops through using a C-style for loop and the index numbers of each item in the associative array's keys, outputting the value of each item.
ls Hello[[.vertical-line.]]World- Nothing, this is an invalid file glob.
-
Hello.vertical-line.World -
Hello[[.vertical-line.]]World -
Hello|World
ls nonexistentfile | grep "No such file" > out.txt- No such file
- ls: cannot access nonexistentfile: No such file or directory
- Nothing, out.txt will be empty.
- It will be the contents of nonexistentfile.
Q42. For the script to print "Is numeric" on screen, what would the user have to enter when prompted?
#!/bin/bash
read -p "Enter text " var
if [[ "$var" =~ "^[0-9]+$" ]];then
echo "Is numeric"
else
echo "Is not numeric"
fi- Any sequence of characters that includes an integer
- The user would have to enter the character sequence of
^[0-9]]+$Only this will prove to be true and "Is numeric" would be printed on the screen due to incorrect syntax. By encapsulating the regular expression in double quotes every match will fail except the text string^[0-9]+$ - One or more characters that only includes integers
- Due to a syntax error it is impossible to get the script to print "Is numeric"
The regex must not be quoted to work properly.
-
history | find cp -
history | grep cp -
grep cp history -
cp history
Q44. In order to write a script that iterates through the files in a directory, which of the following could you use?
-
for i in $(ls); do ... done -
for $(ls); do ... done -
for i in $ls; do ... done -
for $ls; do ... done
Q45. When executing a command and passing the output of that command to another command, which character allows you to chain these commands together?
-
| -
-> -
\# -
@
#!/usr/bin/env bash
greeting="Hello"
echo $greeting, everybody!- a command
- a loop
- a parameter
- a variable
-
(( num -gt 5 )) -
[[$num -lt 5]] -
(( num > 5 )) -
num > 5
$ ls -l
apple
banana
bananapple
banapple
pineapple
strawberry
$ shopt -s extglob
$ ls -l @(ba*(na)|a+(p)le)- a
apple
banana- b
apple
banana
bananapple
banapple
pineapple
strawberry- c
apple
banana
bananappple
banapple
pineapple- d
apple
banana
bananapple
banapple
pineapple- $0
- $# // number of positional parameters
- $$ // pid of the current shell
- $@ // array-like construct of all positional parameters
ls -l
-rwx------+ 1 user1 u1 0 Oct 1 10:00 data.txt- There is an SELinux security context
- The sticky bit is set and the file will stay in RAM for speed
- There is an access control list
- There is an extended attribute such as immutable set
cd -- It moves you to the directory you were previously in.
- It moves you to your home folder (whatever your current working directory happens to be).
- It deletes the current directory
- It moves you one directory above your current working directory.
cat > notes -- Accepts text from standard input and places it in "notes"
- Creates "notes" and exits
- Outputs the content of notes and deletes it
- Appends text to the existing "notes"
VAR="This old man came rolling"
echo "\${VAR//man/rolling}"- This old rolling came rolling
- This old man came man
- This old man came rolling
- This old came
Q54. The shell looks at the contents of a particular variable to identify which programs it can run. What is the name of this variable?
- $INCLUDE
- $PATH
- $PROGRAM
- $PATHS
Shall we play a game? yes\no
-
echo "Shall we play a game? yes/\no" -
echo "Shall we play a game\? yes\\no" -
echo "Shall we play a game? yes\\no" -
echo "Shall we play a game? yes\no"
archive.tar
image1.gif
image1.jpg
image2.gif
image2.jpg
textfile1.txt
textfile2.txt
----------
`shopt -s extglob
rm !(*gif|*jpg)`- a
archive.tar
image1.gif
image1.jpg
image2.gif
image2.jpg
textfile1.txt
textfile2.txt- b
archive.tar
textfile1.txt
textfile2.txt-
c : All of this files will be deleted -
d:
image1.gif
image1.jpg
image2.gif
image2.jpgQ57. The code below seems to work and outputs "8 is greater than 5". However, what unexpected result will tell you it is not functioning properly?
#!/bin/bash
var="8"
if [ $var > 5 ]; then
echo "$var is greater than 5"
fi- There will be no unexpected results. This script works as is and the output will be "8 is greater than 5".
- The comparison will not be able to handle floating-point numbers, as Bash only handles integers. So this example will output an error message if the value of $var is changed to "8.8".
- There will be a file in the current directory named 5.
- The variable $var is not quoted, which will lead to word splitting. This script will fail with a "unary operator expected" message if you change the value of
- It removes the directory 'foo' and the files contained within it.
- It removes all files except those in the current directory.
- It removes all files in the current directory.
- It removes all files except those in the 'foo' directory.
- SELinux policy rules are checked after DAC rules.
- SELinux policy rules are checked before DAC rules
- SELinux policy rules are never checked after DAC rules.
- None of these
w- It doesn't display information about the users currently on the machine.
- It displays information about the users currently on the machine.
- It displays information about the users currently on the another machine.
- None of these
Q61. Which sed options should you use to change the second-to-last instance of variable to rock so it would read:
A constant is a variable that is a rock that isn't variable
var="A constant is a variable that is a variable that isn't variable"
echo "$var" | sed _____-
s/\(.*\)variable\(.*variable\)/\1rock\2/' -
s/variable/rock/' -
s/variable/rock/g' -
s/(.*\)variable\(.*variable\)/\1rock\2/'
- exec script.sh
- chmod +x script.sh
- bash script.sh
- source script.sh
- screen
- screen -X
- screen --shared
- terminal -shared
- ls < filelist.txt
- ls ¦ filelist.txt
- ls > filelist.txt
- ls - filelist.txt
- stop
- esac
- done
- exit
- (command1; command2)
- { command1; command2; }
- (( command1; command2 ))
- command1; command2
echo 'Hello, $(whoami)!'- Hello, $(jon)!
- Hello, jon!
- Hello, $(whoami)!
- Hello, whoami!
-
tar -ssh user@192.158.1.1 /bin/newfile -
tar cvzf - /wwwdata | ssh root@192.168.1.201 "dd of=/backup/wwwdata.tar.gz" - You can't compress the stream
-
scp -r directory user@192.168.1.1:/tmp
-
alias lh='ls -lah' -
link lh='ls -lah' -
alias 'ls -lah'=lh -
lh | ls -lah
Q70. Which statement will print all of the fully qualified .csv files in the home directory or subdirectories while not displaying any errors?
- find $USER_DIR -name "*.csv" 2>/dev/null
- find $HOME -name "*.csv" 1>/dev/null
- find $HOME -name "*.csv" 2>/dev/null
- find HOME -name "*.csv" 1>/dev/null
- that the user is acting as root
- that the current working directory is the root of the file system
- that there are updates for the system available
- that the user is unprivileged
$ ls -l
file10.txt
file1.txt
fileabc.txt
filea.txt
fileb.txt
filec.txt
$ ls -l file[^abc]*.txt- A
file1.txt
file10.txt- B
file10.txt
file1.txt
fileabc.txt
filea.txt
fileb.txt
filec.txt- C
fileabc.txt filea.txt fileb.txt filec.txt- D
filea.txt
fileb.txt
filec.txtReference
The caret (^) symbol here negates matches inside the bracket.
cat <<EOF
------------------------
This is line 1.
This is line 2.
This is line 3.
------------------------
EOF- A
This is line 1.
This is line 2.
This is line 3.- B
------------------------This is line 1.This is line 2.This is line 3.------------------------- C
------------------------
This is line 1.
This is line 2.
This is line 3.
------------------------- D
------------------------
This is line 1.
This is line 2.
This is line 3.
------------------------#!/bin/bash
echo 123446789 > out.txt
exec 3<> out.txt
read -n 4 <&3
echo -n 5 >&3
exec 3>&-- 123446789
- the hyphen symbol (-)
- 123456789
- the number 5, which is written to the file using echo
- $ID
- $#
- $@
- $$
#!/bin/bash
shopt -s extglob
VAR=' This is... a string of characters '
VAR=${VAR##+([[:space:]])}; VAR=${VAR%%+([[:space:]])};
echo "$VAR"
-
<pre> This is... a string of characters</pre> -
<pre> This is...a string of characters</pre> -
<pre>This is... a string of characters</pre> -
<pre>This is...a string of characters</pre>
References:
- What is the meaning of the ${0##...} syntax with variable, braces and hash character in bash?
- What does expanding a variable as "${var%%r*}" mean in bash?
- !
- &&
- &
- $
- -20 to 0
- -20 to 19
- 0 to 19
- 10 to 10
echo $((4/3))
- 1.3
- 1.3333333333
- 1
- 2
- if
- case
- while
- for
cat > notes -- It creates an empty file called "notes" and then exits.
- It outputs the contents of the "notes" file to the screen, and then deletes it.
- It accepts text from the standard input and places it in the "notes" file.
- It appends text to an existing file called "notes."
Q82. You want to match five-letter palindromes such as radar, rotor, and tenet. Which sed option should you use?
- sed -E -n '/^(.)(.)\3\2\1$/p'
- sed -E -n '/^(.)(.)(.).\2\1$/p'
- sed -E -n '/^(.)(.)(.)\2\1$/p'
- sed -E -n '/^(.)(.)(.)(.)\3\2\1$/p'
- shell_add
- save
- echo
- export
[[$A==$B]] [[$A -eq $B]]
- [[$A == $B]] is used for numeric comparisons whereas [[$a-eq $B]] is used for text comparisons.
- [[$A==$B]]is the new way of doing comparison where [[$a-eq $B]]is the legacy syntax.
- they are the same.
- [[$A==$B]]is used for text comparisons whereas [[$a-eq $B]]is used for numeric comparisons.
VAR="united states"
echo "${VAR^}"- unitedstates
- United States
- United states
- UNITED STATES
#!/bin/bash
#condition 1
if [ $foo = "bar" ]; then echo "foo is bar"
fi
#condition 2
if [[ $foo = "bar" ]]; then echo "foo is bar"
fi- Both conditions will fail.
- Both conditions will succeed.
- Condition 1 would succeed and Condition 2 would fail.
- Condition 1 would fail and Condition 2 would succeed.
Explanation: The script as written outputs line 3: [: =: unary operator expected. Define variable and assign value foo="bar", and both conditions will succeed.
-
$# -
$@ -
0 -
$!