2.3 Given a scenario, create, modify, and redirect files

Question 1

grep

Answer 1

Use the grep command to search files for lines that contain a specific pattern. By default, the grep command will display the entire line when it finds a matching pattern

grep “the” /etc/rsyslog.conf

Question 2

cat

Answer 2

The cat command displays the contents of text files

Question 3

tail

Answer 3

The tail command displays the bottom part of text data. By default, the last ten lines are displayed. Use the -n option to display a different number of lines

Question 4

head

Answer 4

The head command displays the top part of text data. By default, the top ten lines are displayed

Question 5

less

Answer 5

The less command is used to display large chunks of text data. Unlike the cat command, the less command will pause after displaying the first page of information. Keys on the keyboard allow the user to scroll through the document

Question 6

more

Answer 6

The more command is a slightly less capable version of the less command. Essentially everything that the more command can do, the less command also has as a feature. However, the less command has additional features that the more command does not have

Question 7

cmd < file

Answer 7

Override STDIN so the input comes from the file specified

Question 8

cmd > file

Answer 8

Override STDOUT so the output goes into the file specified

Question 9

cmd 2> file

Answer 9

Override stderr so the output goes into the file specified.

Question 10

cmd &> file

Answer 10

Override both STDOUT and stderr so the output goes into the file specified.

Question 11

cmd1 | cmd2

Answer 11

Override STDOUT from cmd1 so it goes into cmd2 as STDIN

Question 12

/dev/null

Answer 12

You can redirect these messages into the /dev/null device file. This file is called the “bit bucket” and acts as a trash can that never needs to be emptied. Anything sent to the /dev/null device is immediately discarded

Question 13

/dev/tty

Answer 13

Several files in the /dev directory are used to send data to display devices. These include virtual terminals

Question 14

xargs

Answer 14

The xargs command takes data from STDIN to build and execute commands. Here is the format of the command

input_command | xarg execute_command

The input_command is designed to provide information for xargs to provide as arguments to the execute_command. For example, suppose you want to run the wc -l command on every file in the /etc directory that begins with the letter “e”:

Question 15

tee

Answer 15

If you want STDOUT to be sent both to the terminal and to a file, send the output to the tee command and provide an argument that indicates the file in which you want to store the information.

Question 16

awk

Answer 16

head /etc/passwd | awk -F: ‘{print $1,$7}’

root /bin/bash
bin /sbin/nologin
daemon /sbin/nologin
adm /sbin/nologin
lp /sbin/nologin
sync /bin/sync
shutdown /sbin/shutdown
halt /sbin/halt
mail /sbin/nologin
operator /sbin/nologin

Question 17

sed

Answer 17

Use the sed utility to make automated modifications to files. The basic format for the sed command is sed ‘s/RE/string/’ file