06 Redirection

Question 1

What is the function of the “cat” command

Answer 1

Concatenate files

Question 2

What is the function of the “sort” command

Answer 2

Sort lines of text

Question 3

What is the function of the “uniq” command

Answer 3

Report (or omit) repeated lines

Question 4

What is the function of the “grep” command

Answer 4

print lines of text matching a given pattern

Question 5

What is the function of the “wc” command

Answer 5

Performs a word count; yields newlines, word count, and byte count of a file

Question 6

What is the function of the “head” command

Answer 6

print ‘n’ lines from the beginning of a file

Question 7

What is the function of the “tail” command

Answer 7

print the last ‘n’ lines from a file

Question 8

What is the function of the ‘tee’ command

Answer 8

read from stdin, write to stdout AND to a file

Question 9

Program output consists of what two types of data?

Answer 9

1. Program execution results

2. Status/error messages

Question 10

Programs send their output to a special file (typically the screen), known as … ?

Answer 10

Standard Output

Question 11

What is the REDIRECTION operator?

Answer 11

>

Question 12

What is the APPEND operator?

Answer 12

> >

Question 13

If standard error has a file descriptor of ‘0’, where does the output go?

Answer 13

A file descriptor of ‘0’ sends error output to standard input

Question 14

If standard error has a file descriptor of ‘1’, where does the output go?

Answer 14

A file descriptor of ‘0’ sends error output to standard output

Question 15

If standard error has a file descriptor of ‘2’, where does the output go?

Answer 15

A file descriptor of ‘0’ sends error output to standard error

Question 16

Assuming you give the command:

“ls -l /bin/usr 2> ls-error.txt”

Describe the output

Answer 16

list the contents of /bin/usr, which does not exist,

take the output that would’ve gone to standard error, and write it out as a new file ls-error.txt

Question 17

You issue the ‘cat’ command with no arguments. Describe what the system is doing…

Answer 17

Cat is reading from stdin (waiting for keyboard input)

Question 18

What is a ‘pipeline’

Answer 18

connects stdout to stdin of the next command

Question 19

What is the difference between ‘>’ and ‘|’ ?

Answer 19

Redirection connects a command to a file

A Pipeline connects the output of one command with the input of the next command.

Question 20

Describe the output of this command:

ls /bin /usr/bin | sort | less

Answer 20

1. Create two directory listings (/bin, /usr/bin), passed to sort
2. Sort command yields a single, sorted list; passed to ‘less’ command
3. less outputs that single sorted list to screen

Question 21

Describe the output of the following command:

ls /usr/bin | tee ls.txt | grep zip

Answer 21

1. list directory /usr/bin; passed to ‘tee’
2. ‘tee’ writes directory listing to ls.txt, passes output to grep
3. Grep searches the directory listing for “zip”, writes matched lines to screen