Bash Commands

Question 1

vim -r

Answer 1

list swap files

Question 2

tail ‘file’

Answer 2

shows last 10 lines of the file

Question 3

vim

Answer 3

open or creates file

Question 4

mv ‘file1’ ‘file2’

Answer 4

move file to destination or rename file

Question 5

cp ‘file1’ ‘file2’

Answer 5

copy contents from file1 to file2

Question 6

rm ‘file’

Answer 6

remove a file

Question 7

rm -r ‘file’

Answer 7

remove a file recursively

Question 8

rm -d

Answer 8

remove empty directory

Question 9

rm – -foo

Answer 9

rm file that starts with foo

Question 9

find . -name ‘file1’ -type d

Answer 9

find the directory called file1. Without the -type d, it will search for files and directories

Question 10

diff ‘file1’ ‘file2’

Answer 10

compares files and shows where they are different

Question 11

sort -n -r ‘file’

Answer 11

sort files, -n for numeric sort and -r for reversing order

Question 12

rev

Answer 12

reverse string character

Question 13

chmod +wrx

Answer 13

reach, write and execute permissions

Question 14

chmod -o -g -a -u

Answer 14

removes permission for others not in group, group, all users and user

Question 15

lpr ‘filename’

Answer 15

prints the file

Question 16

grep -i ‘hello’ ‘filename’

Answer 16

search for hello in filenames (this will not be case-sensitive)

Question 17

grep -r ‘hello’ ‘directory

Answer 17

search recursively for pattern in the directory

Question 18

sed ‘s/hello/goodbye/g’ ‘filename’

Answer 18

This will replace all occurrences of hello with goodbye in ‘filename’ without modifying the file

Question 19

sed -i ‘s/dog/cat/g’ file.txt

Answer 19

replaces “dog” with “cat” in file.txt and saves the change

Question 20

echo “this” | sed ‘s/is/at/g’

Answer 20

replaces “is” with “at” in the input string “this”

Question 21

mkdir ‘filename’

Answer 21

makes a new directory

Question 22

rmdir -rf

Answer 22

removes a non-empty directory

Question 23

cp -r ‘dir1’ ‘dir2’

Answer 23

copy dir1 into dir2 including subdirectories

Question 24

pwd

Answer 24

print working directory

Question 25

cd ~

Answer 25

changes to home directory

Question 26

whoami

Answer 26

returns your username

Question 27

sudo command

Answer 27

execute command as the root user

Question 28

lsof

Answer 28

lists all open files

Question 29

varname=value

Answer 29

defines a variable

Question 30

echo $varname

Answer 30

checks a variables value

Question 31

read -p “Please enter your name: “ name

Answer 31

prompts the user for input with a specified message and stores the entered value in a variable

Question 32

export -f ‘f1’

Answer 32

export function called f1

Question 33

How do you define an array

Answer 33

array[0]=valA

Question 34

How do you display the array’s value for a certain index

Answer 34

${array[i]}

Question 35

what do you put at the beginning of your bash script

Answer 35

!/bin/bash

Question 36

what are some arguments for chmod

Answer 36

–recursive - changes files and directories recursively
–changes - report when a change is made
–silent - suppress most error messages

Question 37

what does apropos keyword mean?

Answer 37

Its when you don’t know the command name but roughly know what you want to do.

Question 38

man 3 printf

Answer 38

this will open up the third man page of the prinf command

Question 39

what does rm file* do?

Answer 39

removes files 1 to infinity that have digits after the filename. Ex: file1 file2

Question 40

rm file?

Answer 40

removes files with one character after filename. files{0-9}

Question 41

*(abc)

Answer 41

would match “”, “abc”, “abcabc”, “abcabcabc”, etc.

Question 42

+(abc)

Answer 42

would match “abc”, “abcabc”, “abcabcabc”, but not an empty string “”

Question 42

?(abc)

Answer 42

would match “” or “abc”.

Question 43

@(abc|def)

Answer 43

would match “abc” or “def”, but not both or neither

Question 44

!(abc)

Answer 44

would match any string that is not “abc”

Question 45

what is the AND operator and the OR operator

Answer 45

&& - AND || - OR

Question 46

str1 == str2

Answer 46

the strings match each other

Question 47

what are the terms for less than, greater than or equal to, not equal, etc..

Answer 47

-lt # less than
-le # less than or equal
-eq # equal
-ge # greater than or equal
-gt # greater than
-ne # not equal

Question 48

what is the criteria in starting and stopping a for loop

Answer 48

do and done

Question 49

what are the requirements in an if statement

Answer 49

if condition
then
statements
[elif condition
then statements…]
[else
statements]
fi

Question 50

how do you do an incremental for loop in bash

Answer 50

for (( initialisation ; ending condition ; update ))

Question 51

what does the pipe function do for this example cmd1 | cmd2

Answer 51

This takes the results from cmd1 and sends them to cmd2

Question 52

what happens here? ls | grep “.txt”

Answer 52

ls lists all the files, and grep “.txt” looks through that list to find only the text files.

Question 53

history

Answer 53

show command history

Question 54

source /file

Answer 54

runs every command one line at a time

Question 55

!!

Answer 55

repeats the last command

Question 56

echo $SHELL

Answer 56

displays the shell you are using

Question 57

echo $PATH

Answer 57

shows the entire path you are in

Question 58

whereis bash

Answer 58

shows location, source code and path

Question 59

ls

Answer 59

list files in directory

Question 60

env

Answer 60

displays environment variables

Question 61

what outputs when ls -l is printed to the console

Answer 61

displays
type of file
type of permission access
ACL flag
Links
Owner
Group
Size
Date and Time
Filename

Question 62

ls - a

Answer 62

displays hidden files

Question 63

ln -s ‘filename’ ‘link’

Answer 63

creates link to a file

Question 64

readlink ‘filename’

Answer 64

shows where the link points to

Question 65

tree

Answer 65

shows directories in the tree format

Question 66

touch file

Answer 66

creates or updates your file

Question 67

cat file

Answer 67

displays raw contents of file

Question 68

cat -n file

Answer 68

shows numbers of lines

Question 69

nl file

Answer 69

shows number of lines in file

Question 70

cat f1 > f2

Answer 70

copy f1 to f2

Question 71

cat f1&raquo_space; f2

Answer 71

merge 2 file texts together

Question 72

echo “New entry” > file2

Answer 72

directs and overwrites New entry to file2

Question 73

file1&raquo_space; file2

Answer 73

directions and appends contents of file1 to file2

Question 74

more file1

Answer 74

shows the first portion of the file1

Question 75

head file1

Answer 75

shows the first 10 lines of file1

Question 76

tail file1

Answer 76

shows the last 10 lines of file1

Question 77

What does filename=$(basename “$file” .txt) accomplish?

Answer 77

removes the .txt extension from the filename and stores the result in the variable filename

Question 78

what does mkdir -p /path/to/directory

Answer 78

If /path/to/ does not exist, it will create both path, to, and directory. If directory already exists, it won’t raise an error.

Question 79

When calling a variable in your bash script that has already been initialized, what 2 things must you always include? Lets call the variable filename

Answer 79

for “$filename” in …..

Question 80

You must always do what 2 things when writing an if/elif/else statement in bash?

Answer 80

Use []; if [ “$file” -gt 6];

Question 81

What does ./mean < “$input_file” > “$output_file” do?

Answer 81

executes the mean program, taking input from input_file and saving the output to output_file

Question 82

what does echo “hello” | tr “aeiou” “12345”

Answer 82

translates the vowels a, e, i, o, u in the string “hello” into the numbers 1, 2, 3, 4, and 5. The output would be h2ll4

Question 83

what is an example of a file you are looking for when you say grep -r “multiply(.,.,.*)”

Answer 83

multiply(1, 2, 3)

Question 84

what would this function be looking for? grep “multiply(.,.,.*)” math
And what we be in the contents?

Answer 84

example_math

Contents:
multiply(1,2,3)

Question 85

What does ‘s/[0-9]kg,/&&/g’ do?

Answer 85

finds occurrences of a digit followed by “kg,” and a comma in a text and replaces them with the same matched content

Question 86

What happens if you run multiple commands with the > operator sequentially on the same file?

Answer 86

The contents of the file will be overwritten by the output of the last command executed.

Question 87

What does the command command 2> error_log do?

Answer 87

runs command and redirects any error messages (stderr) to a file named error_log

Question 88

How can you redirect both standard output and standard error to a single file?

Answer 88

command > output_file 2>&1

Question 89

what does this function do, ls | tee directory.txt | sort

Answer 89

Lists the contents of the current directory, saves that list to a file called directory.txt, and displays the sorted output in the terminal.

Question 90

what does, cat file | command do?

Answer 90

reads the contents of file and pipes that content into command for further processing

Question 91

How does the uniq command work?

Answer 91

uniq filters out repeated lines in a sorted file, displaying only unique lines or the number of occurrences.

Question 92

what will the results of this input be? seq 2 2 20

Answer 92

2
4
6
8
10
12
14
16
18
20

Question 93

What is the purpose of the awk function?

Answer 93

It helps you look at specific sets of data and do things with that information. You can tell it what to find and what to do with it.

Question 94

If your file contains:
Alice 88
Bob 92
Charlie 67
Diana 85
Eve 95

What will this function produce?

awk ‘$2 > 90 { print $1 }’ grades.txt

Answer 94

Bob
Eve

Question 95

If your file contains:
Alice 88
Bob 92
Charlie 67
Diana 85
Eve 95

What will this prompt produce?

awk ‘{
if ($2 > max) {
max = $2;
name = $1;
}
} END { print “Top scorer:”, name, “with a score of”, max }’ grades.txt

Answer 95

Top scorer: Eve with a score of 95

Question 96

what does this while loop do?

count=1
while [ $count -le 5 ]; do
echo “Count $count”
((count++))
done

Answer 96

Count 1
Count 2
Count 3
Count 4
Count 5

Question 97

What does the command wc file.txt do?

Answer 97

counts the number of lines, words, and characters in the file file.txt, displaying the results in three columns:

Question 98

What does the command basename /home/user/documents/report.txt return?

Answer 98

report.txt

Question 99

what does chmod -R do?

Answer 99

Apply the permission change recursively to all the files and directories within the specified directory.

Question 100

what does chmod -c do?

Answer 100

It will display a message for each file that is processed. while indicating the permission change that was made.

Question 101

what does chmod -f do?

Answer 101

It helps in avoiding display of error messages.

Question 102

what does chmod -h do?

Answer 102

Change the permissions of symbolic links instead of the files they point to

Question 103

What does the -c option do in tar?

Answer 103

It creates an archive by bundling files and directories together.

Question 104

What does the -x option do in tar?

Answer 104

It extracts files and directories from an existing archive.

Question 105

What does the -f option do in tar

Answer 105

It specifies the filename of the archive to be created or extracted.

Question 106

What does the -v option do in tar?

Answer 106

It shows extra details about what’s happening while files are being added to or taken out of the archive

Question 107

What does the -r option do in tar?

Answer 107

It updates or adds files or directories to an already existing archive without recreating the entire archive.

Question 108

what numbers represent the rwx commands?

Answer 108

A 1 gives execute permission, a 2
gives write permission, and a 4
gives read permission

Question 109

what does the chown command do?

Answer 109

Change owner of file/dir
(admin only)

Question 110

what does chgrp do?

Answer 110

Change group of a file/dir

Question 111

What’s an ACL?

Answer 111

ACLs provide more granular control over file access than traditional permissions, but may not be necessary for all systems.