Topic 5 - Unix Input-Output Redirection

Question 1

During execution of a program, where are the input/output/errors directed to?

Answer 1

They're directed from/to:
Standard Output (stdin)
Standard Output (stdout)
Standard Error (stderr)

Question 2

Where can these outputs be redirected to?

Answer 2

Any file or device other than the terminal

Question 3

What is the redirect output symbol?

Answer 3

>

Question 4

What is the append output symbol and what does it do?

Answer 4

> >

• instructs the shell to add the new data to the end of a file, accumulating on any data that was already there

Question 5

Can standard output be redirected independently from standard error?

Answer 5

Yes

Question 6

How do you redirect in bourne-style shells?

Answer 6

standard error = 2>
standard output = 1> or simply >
Can use 2>&1 to re-direct to the same name file

Question 7

How you append in bourne-style shells?

Answer 7

2» instead of 2>
1» instead of 1>
» instead of >

Question 8

How do you redirect in C-style shells?

Answer 8

redirected together to a file using “>&”;;
Independently: two files as follows:
( cat file3 file2 > output_file ) “>&”; error_file

Question 9

How do you append in C-style shells?

Answer 9

> > &; instead of >&;

|&raquo_space; instead of >

Question 10

What is the Redirect Input symbol ?

Answer 10

less than sign

Question 11

Standard input can also be redirected from the text to be written immediately after the command using the ______.

Answer 11

two less than signs

Question 12

What does the command tr do?

Answer 12

means translate: reads from standard input, modifies selected characters in the read input, writes the results to standard output.

Question 13

What does the command grep do?

Answer 13

Global Regular Expression and Print. searches text files for matching pattern and prints matched patters to standard output.

Question 14

What is the difference between wildcards and regex?

Answer 14

File name wildcards are interpreted and matched by shells. Regex are interpreted and matched by special utilities.

Question 15

What does the wc command do

Answer 15

prints the number of lines,w words, and bytes in a file.

Question 16

What does the sort command do

Answer 16

sort all input lines in alphabetical order. Write the result to the standard output.

Question 17

What does the uniq command do

Answer 17

removes duplicated lines from a sorted file, writes the result to the standard output.

Question 18

What is a pipe?

Answer 18

Connects standard output of one program to standard input of another. General Form: command1 | command 2

Question 19

Describe the tee command.

Answer 19

tee - replicates the standard output like a T connection:
cat read.txt
cat read.text > myfile

cat read.txt | tee myfile

Question 20

what is /dev/null?

Answer 20

a virtual file that is always empty - redirecting to here means discard errors