Linux Commands

Question 1

$ exit

Answer 1

closes the terminal emulator window

Question 2

$ date

Answer 2

displays the current time and date

Question 3

$ cal

Answer 3

displays a calender of the current month

Question 4

$ pwd

Answer 4

prints full path of current working directory

Question 5

$ cd

Answer 5

changes directory (to root without giving pathname)

Question 6

$ ls

Answer 6

lists directory content

Question 7

$ cd /some/path/name

$ cd ~/some/path/name

Answer 7

changes directory by given absolut path, which starts with the root “/” or with ~ as representation of the root followed by some directories

Question 8

.

..

Answer 8

one dot represents the current working directory

two dots represent the parent directory of the current working directory

Question 9

1. absolute pathname

2. realtive pathname

Answer 9

1. an absolute pathname starts from the root directory /
2. a relative pathname starts from the working directory . /
   In almost all cases, we can omit the ./ part because it is implied because ./ means the working directory, but we start a relative part always from the working directory. Simply wrinting “ cd name_of_subdirectory” is enough.

Question 10

How can you see hidden files?

Answer 10

Filenames that begin with a period character are hidden. This means that “ls” will not list them unless you enter “ls -a”.

Question 11

How should filenames be written in Linux?

Answer 11

Filenames and commands in Linux are case sensitive. Most important, do not embed spaces in filenames. If you want to represent spaces between words in a filename, use underscore characters. File extensions are not necessary.

Question 12

$ cd -

Answer 12

changes the working directory to the previous working directory

Question 13

$ cd ~user_name

Answer 13

changes the working directory to the home directory of user_name

Question 14

$ ls

Answer 14

lists content of working directory

Question 15

$ ls /some/path/name

Answer 15

lists the content of the directory, specified by this pathname, without changing the current working directory

Question 16

$ ls -l

Answer 16

lists the content in long detailed form of the working directory

Question 17

1. $ ls -lt

2. $ ls -lt –reverse

Answer 17

1. lists the content in long detailed form “-l” and sorts the content by the modification time “-t” of the current working directory
2. reverses the order of the sorted content

Question 18

$ ls -a (–all)

Answer 18

lists all files, even those with names that begin with a period, which are normally not listed (that is, hidden)

Question 19

$ ls -A (–almost-all)

Answer 19

lists like the -a option hidden files except it does not list .(current directory) and ..(parent directory)

Question 20

$ ls -d (–directory)

Answer 20

Ordinarily, if a directory is specified, ls will list the contents of the directory, not the directory itself. Use this option in conjunction with the -l option to see details about the directory rather than its contents.

Question 21

$ ls -F (–classify)

Answer 21

This option will append an indicator character to the end of each listed name. For example, it will append a forward slash (/) if the name is a directory.

Question 22

$ ls -h (–human readable)

Answer 22

In long format listings (in combination with -l), displays file sizes in human-readable format rather than in bytes.

Question 23

$ ls -r (–reverse)

Answer 23

Displays the content of the working directory in reverse order. Normally, ls displays its results in ascending alphabetical order.

Question 24

$ ls -S

Answer 24

Sorts the content of the working directory by file size.

Question 25

$ ls -t

Answer 25

Sorts the content of the working directory by modification time.

Question 26

$ file name_of_file

Answer 26

The file command will print a brief description of the file’s (name_of_file) contents.

Question 27

$ less name_of_file

Answer 27

The less command is a program to view text files, like configuration files, program-scripts, etc. If we accidently attempt to view a non-text file and it scrambles the terminal window, we can recover by entering the “reset” command.

Question 28

$ less name_of _file

Name typical less commands, that can be used once the less programm starts and enables the view of the content of the file (name_of_file).

Answer 28

PAGE UP or b Scroll back one page
PAGE DOWN or space Scroll forward one page
Up arrow Scroll up one line
Down arrow Scroll down one line
G Move to the end of the text file
1G or g Move to the beginning of the text file
/characters Search forward to the next occurrence of characters
n Search for the next occurrence of the previous search
h Display help sreen
q Quit less

Question 29

What is the copy-and -paste trick when using a mouse?

Answer 29

If you are using a mouse, you can double-click a filename to copy it and middle-click to paste it into commands.

Question 30

What is the meaing of this wildcard: *

Answer 30

• Matches any characters

Question 31

What is the meaning of this wildcard: ?

Answer 31

? Matches any single character

Question 32

What is the meaning of this wildcard: [characters]

Answer 32

[characters] Matches any character that is a member of the set characters

Question 33

What is the meaning of this wildcard: [!characters]

Answer 33

[!characters] Matches any charachter that is not a member of the set characters

Question 34

What is the meaning of this wildcard: [[:class:]]

Answer 34

[[:class:]] Matches any character that is a member of the specified class

Question 35

Name commonly used character classes

Answer 35

[:alnm:] Matches any alphanumerical character
[: alpa:] Matches any alphabetic character
[:digit:] Matches any numeral
[:lower:] Matches any lower case letter
[:upper:] Matches any uppercase letter

Question 36

How can you select all files of a directory?

Answer 36

*

Question 37

How can you select any file beginning with “ g “?

Answer 37

g*

Question 38

How can you select any file beginning with “ b “ followed by any characters and ending with “ .text “ ?

Answer 38

b*.txt

Question 39

How can you select any file beginning with either “ a “, or “ b “, or “ c “ ?

Answer 39

[abc]*

Question 40

How can you select any file beginning with “ Data “ followed by exactly three characters?

Answer 40

Data???

Question 41

How can you select any file beginning with “ BACKUP. “ followed by exactly three numerals?

Answer 41

BACKUP. [0-9][0-9][0-9]

Question 42

How can you select any file beginning with an uppercase letter?

Answer 42

[[:upper:]]*

Question 43

How can you select any file beginning with a numeral?

Answer 43

[![:digit:]]*

Question 44

How can you select any file ending with a lowercase letter or the numerals 1, 2, or 3?

Answer 44

*[[:lower:]123]

Question 45

How can you create a directory?

Answer 45

$ mkdir name_of _directory

Question 46

How can you create three directories named dir1, dir2, dir3?

Answer 46

$ mkdir dir1 dir2 dir3

Question 47

How can you copy the single file or directory “item1” to the file or directory “item2”?

Answer 47

$ cp item1 item2

Question 48

How can you copy “item1”, “item2” and “item3” to the directory “dir1” ?

Answer 48

$ cp item1 item2 item 3 dir1