CL Extras

Question 1

What does the cal command do?

Answer 1

prints out a calendar

Question 2

What would you type if you wanted to see the current year’s calendar?

Answer 2

cal -y

Question 3

What would you do if you wanted to display the calendar of a different year?

Answer 3

cal 2015

Question 4

How can you display the month of a year?

Answer 4

pass two integer parameters:

cal 8 2016 = august 2016

Question 5

What command will print out the contents of a file to standard output?

Answer 5

cat

Question 6

How can you send the output of cat to a file?

Answer 6

cat file1.txt file2.txt > new_file.txt

Question 7

How can we print to the screen a file’s contents with line numbers added?

Answer 7

cat -b file.txt

Question 8

What is the default signal for kill?

Answer 8

15 or SIGTERM

Question 9

How can we find the process ID of the process that we need to stop?

Answer 9

ps command shows PID

Question 10

What does this command do:

kill 123456

Answer 10

It sends a signal to process 123456 to peacefully shut down when it is ready.

Question 11

What two ways can you pass a signal to the kill command?

Answer 11

with the value of the signal or by using the -s flag and passing the name of the signal.

kill -9 123456

kill -s SIGKILL 123456

Question 12

What command prints out information about commands?

Answer 12

man

syntax: $ man command_you_want_to_learn_about

Question 13

What command allows us to look at the end of a file?

Answer 13

Tail

Question 14

What is the tail command good for?

Answer 14

monitoring log files in a production environment

Question 15

By default, when you pass a file name to the tail command, the last __ lines of a file will be printed to the screen, and ___.

Answer 15

10

tail will exit.

Question 16

How do we change the number of lines that are displayed by tail?

Answer 16

with the -n flag

tail -n 5

Question 17

How can we reverse the direction of how tail displays the selected lines of the file to us?

Answer 17

with the -r flag

tail -r -n 5 /path/filename displays the last five lines of the file with the last line first

Question 18

What flag makes the tail command go live, continuing to output new data as it is added to the end of a watched file?

Answer 18

-f

tail -f /path/file.log

Question 19

What is a live file referred to?

Answer 19

A ‘tailing’ file.

Question 20

How can we filter the live output of a tail command?

Answer 20

tail -f /path/name.log | ag com.apple.windowserver

Question 21

What command allows you to recursively list the contents of a directory in a high level view?

Answer 21

tree

Question 22

How can you limit the depth of tree’s recursion?

Answer 22

with the -L flag

tree -L 2 will only display the first two levels of a tree of directories

Question 23

By default tree will list both files and directories, how can we print out just the directories?

Answer 23

with the -d flag

tree -d

Question 24

How can we count the number of words in a file?

Answer 24

wc -w filename.txt

Question 25

How can we count the number of lines in a file?

Answer 25

wc -l file

Question 26

How can we see in how many lines the pattern DHH is repeated?

Answer 26

ag DHH | wc -l