Basic Commands

Question 1

What does the [cat] command do?

Answer 1

It lists the contents of a file.

Question 2

What is a [stream]?

Answer 2

A source of input or output that processes use to read or write data.

Question 3

What is difference between the commands: [CTRL-D] and [CTRL-C]?

Answer 3

[CTRL-D] tells the running process that it has reached the EOF (End of File) and this usually terminates the process because it cannot receive any further input.

[CTRL-C] terminates the process regardless of its input/output stream.

Question 4

What do [stdin] and [stdout] mean?

Answer 4

Standard Input (Default Input source)
Standard Output (Default Output Source)

Question 5

Where do many commands read from if you do not specify an input file?

Answer 5

[stdin] Standard Input - The Default Input Source.

Question 6

Where do programs send output?

Answer 6

Some programs send output to stdout (like [cat]).

Others send output directly to files.

Question 7

What is the third standard I/O stream?

Answer 7

Standard Error

Question 8

What is the best feature of standard streams?

Answer 8

You can easily modify them to read or write data to streams other than the terminal.

Question 9

What does the [ls] command do?

Answer 9

It lists all the contents of a directory. By default, this is set to the current directory (input stream).

Question 10

Is the [ls] command limited to the current directory?

Answer 10

No. I can change the program’s argument from the default current directory to any other file or directory.

Question 11

What does [ls -l] argument do?

Answer 11

It gives a detailed (long) list of the contents of a directory.

Question 12

What doe the [ls -F] argument do?

Answer 12

It gives details of file types in a list.

Question 13

What does the [cp] command do?

Answer 13

It copies files.

Question 14

Using the [cp] command, what is the syntax for copying one file to another?

Answer 14

[cp file1 file2]

Question 15

Using the [cp] command, what is the syntax for copying one file to a directory?

Answer 15

[cp file dir]

Question 16

What does the [mv] command do?

Answer 16

It moves (cuts) files/directories from one location to another.

Question 17

What does the [echo] command do?

Answer 17

It displays whatever text you type in the terminal.

Question 18

What does the [touch] command do?

Answer 18

It creates a new file. If the target file already exists [touch] doesn’t change the file, but it modifies its date of creation.

Question 19

What is the syntax for the [touch] command?

Answer 19

[touch filename]

Question 20

What does the [rm] command do?

Answer 20

It removes (deletes) a file.

Question 21

Where does the unix directory hierarch start?

Answer 21

It starts at [/] called the root directory.

Question 22

What is the directory seperator?

Answer 22

The slash [/]

Question 23

What does it mean to refer to a file or directory?

Answer 23

You are specifying its [path], or [pathname].

Question 24

What does it mean when a path starts with a [/], such as [/usr/lib]?

Answer 24

That means it’s a full or absolute path.

Question 25

What does a path component identified by two dots (..) do?

Answer 25

It specifies the parent of a directory.
Example
If in [/usr/lib] [../lib] refers to /usr/bin.

Question 26

What does one dot (.) refer to?

Answer 26

It refers to the current directory.

Question 27

Why won’t you have to use the single dot (.) very often?

Answer 27

Because most commands default to the current directory.

Question 28

What is a path beginning without [/] called?

Answer 28

It is called a relative path.

Question 29

What is the current working directory?

Answer 29

It is the directory that a process is currently running in.

Question 30

What does the [pwd] command do?

Answer 30

It shows me my current working directory.

Question 31

What does the [cd] command do?

Answer 31

It changes the shell’s current working directory.

Question 32

What is the syntax for the [cd] command?

Answer 32

[cd dir]

Question 33

What happens if you omit the name of a directory when using the [cd] command?

Answer 33

The command defaults to its default stdin argument and returns me to my home directory.

Question 34

What do some programs abbreviate the home directory to?

Answer 34

A tilde (~) symbol.

Question 35

Why is the [cd] command considered a shell built-in that wouldn’t work as a separate program?

Answer 35

Because if it were to run as a subprocess, it could not (normally) change its parent’s current working directory.
NOTE: There are times when knowing this fact can clear up confusion.

Question 36

What does the [mkdir] command do?

Answer 36

It creates a new directory.

Question 37

What does the [rmdir] command do?

Answer 37

It removes (deletes) directories.

Question 38

What is the limitation of the [rmdir] command?

Answer 38

It cannot delete directories that are not empty.

Question 39

What does the [rm -r] command do?

Answer 39

It deletes a directory whether or not its empty.

Question 40

What is Globbing?

Answer 40

The process of matching simple patterns to file and directory names.

Question 41

What does the asterisk (*) glob character do?

Answer 41

It tells the shell to match any number of arbitrary characters.

Question 42

What does the question mark (?) glob character do?

Answer 42

It instructs the shell to match exactly one arbitrary character.