Shell Features

Question 1

What are the 3 channels every linux program has when it starts?

Answer 1

File Desciptors
stdin 0<
stdout 1>
stderr 2>

Question 2

How would you overwrite text to a file from the shell?

Answer 2

1> - stdout

i.e echo “Overwrite this.” 1> file.txt

Question 3

How would you append text to a file from the shell?

Answer 3

1» - stdout

i. e ls -alh 1» file.txt
i. e echo “Append this.” 1» file.txt

Question 4

How would you append error output to a text file from the shell?

Answer 4

2»

i.e ls -alh nonexistant 2» file.txt

Question 5

How would you overwrite error output to a text file from the shell?

Answer 5

2>

i.e ls -alh nonexistant 2> file.txt

Question 6

How do you run a command sequentially after the other?

Answer 6

;

i.e ifconfig; touch file

Question 7

How do you run a command sequentially only if the first completed successfully?

Answer 7

&&

i.e ls file && mkdir directory1

Question 8

What is the command to search for text?

Answer 8

grep

i. e grep example file.txt
i. e grep example ./* -all files in current directory

Question 9

What is the command to count the number of characters and words in a file?

Answer 9

wc

Question 10

How do you pass the output from one command to another?

Answer 10

|

i.e cat file | sort

Question 11

What is the command to select only portions of text from a file?

Answer 11

cut

i.e cat file | cut -d’ ‘ -f3,4

Question 12

What is the command to only display unique text?

Answer 12

uniq

i.e cat file | uniq

Question 13

What is the command to run a subsequent command only of the previous failed?

Answer 13

||
ls -l nonexistent || touch nonexistent
*or operator evaluates expressions either side