Chapter 1 - Exploring Linux Command-Line Tools

Question 1

what is the shell?

1-4

Answer 1

a program that accepts and interprets text-mode commands and provides an interface to the system

Question 2

what are shell environment variables?

1-4

Answer 2

placeholders for data that may be useful to many programs

Question 3

in linux, what is the most popular shell?

1-5

Answer 3

bash

Question 4

there are 2 types of default shells: the default interactive shell and the default system shell. explain the difference between the 2 by describing their functions

1-5

Answer 4

default interactive shell - user uses this to enter commands, run programs from the command line, run shell scripts

default system shell - used by Linux to run system shell scripts

Question 5

tell me the difference between internal and external commands

1-6

Answer 5

internal - also known as built-in commands, allow you to perform common tasks like changing the directory, timing an operation, setting options, and terminating the shell

external - commands that are not built-in

Question 6

what happens when you type a command that is not recognized by the shell as one of its internal commands?

1-8

Answer 6

the shell checks its path to find a program by that name to execute it

Question 7

you have hit Ctrl+R to begin a backward search. what do you hit to terminate the search?

1-10

Answer 7

Ctrl+G

Question 8

how do you retrieve the last command in your shell history?

1-11

Answer 8

type !!

Question 9

how do you retrieve the last 500 commands entered?

1-11

Answer 9

type history

Question 10

bash configuration files are actually bash ____ ____

1-13

Answer 10

shell scripts

Question 11

which environment variable provides the shell with a directory list to search when you’re entering command or program names?

1-14

Answer 11

$PATH

Question 12

you can’t remember the exact name of a command to look up. the man utility has an option to help you out. what is that option?

1-15

Answer 12

the -k option

Question 13

your Linux is missing its whatis database. what do you do?

1-15

Answer 13

type makewhatis at the prompt

Question 14

there are file descriptors for standard input, output, and error. what are they?

1-17

Answer 14

input - 0
output - 1
error - 2

Question 15

what keystroke corresponds to an end-of-file marker?

1-19

Answer 15

Ctrl+D

Question 16

what is the | symbol for?

1-19

Answer 16

for redirecting a program’s output to another program’s input

Question 17

tell me the syntax for xargs command for building a command from its standard input

1-20

Answer 17

xargs [options] [command [initial-arguments]]

Question 18

the cat command is used for combining files, but its also commonly used for what?

1-22

Answer 18

to display the contents of a short file to STDOUT

Question 19

how does the join command work?

1-23

Answer 19

it combines two files by matching the contents of specified fields within the fields

Question 20

which command allows you to display a file as octal numbers?

1-25

Answer 20

od

Question 21

which command allows you to break a file into pieces?

1-26

Answer 21

split

Question 22

which command lets you change characters from standard input?

1-27

Answer 22

tr

Question 23

which 3 commands are used for reformatting the text in a file?

1-28

Answer 23

fmt, nl, and pr

Question 24

what does the grep file do?

1-36

Answer 24

it searches for files that contain a specified string and returns the name of the file and a line of context for that string

Question 25

what is sed used for?

1-38

Answer 25

directly modifies a file’s contents, sending the hanged file to standard output

Question 26

you type a command into bash with a long file name, and the screen comes back “file not found”. what do you do?

1-42

Answer 26

retype the command, extra carefully
retype the command, using the Tab key
press Up arrow and use bash’s editing features to correct the typo

Question 27

cat, less, tee, sed, and echo. which are internal, which are external?

1-42

Answer 27

echo is internal, all the rest are external

Question 28

you type echo $PROC, the computer says Go away. what happened?

1-42

Answer 28

the $PROC environment variable has somehow been set to Go away

Question 29

what does the pwd accomplish?

1-42

Answer 29

prints the name of the working directory

Question 30

what is the surest way to run a program that’s located in the current working directory?

1-42

Answer 30

type ./ followed by the program name (run it all together)

Question 31

how does man display information by default on most linux systems?

1-43

Answer 31

it uses the less pager

Question 32

you want to store the output of the ifconfig command in a text file called file.txt for future reference, and you want to wipe out any existing data in the file. you don’t want to store standard error in this file, so how can you accomplish all of this?

1-43

Answer 32

ifconfig > file.txt

use the redirect symbol

Question 33

what is the effect of the following command:
$myprog &> input.txt

1-43

Answer 33

the standard output and standard error from myprog are written to input.txt

Question 34

how many commands can you pipe together at once?

1-43

Answer 34

far more than 16

Question 35

you want to run an interactive script called gabby which produced a lot of output in response to the user’s inputs. to facilitiate future study of this script, you want to copy its output to a file. how do you do this?

1-43

Answer 35

gabby | tee gabby-out.txt

Question 36

a text-mode program, verbose, prints a lot of bogus “error” messages to standard error. how might you get rid of those messages while still interacting with the program?

1-44

Answer 36

verbose 2> /dev/null

Question 37

how do the > and&raquo_space; operators differ?

1-44

Answer 37

> will create a new file or overwrite an existing one

|&raquo_space; creates a new file or appends to an existing one

Question 38

what program would you use to display the end of a configuration file?

1-44

Answer 38

tail

Question 39

what is the effect of the following command?

$ pr report.txt | lpr

1-44

Answer 39

the file report.txt is formatted for printing and sent to the lpr program

Question 40

which of the following commands will number the lines in aleph.txt? there are 3 ways to do it.

1-44

Answer 40

nl aleph.txt
cat -b aleph.txt
cat -n aleph.txt

Question 41

you have a data file, data.txt, to be processed by a particular program. however, the program cannot handle data separated by tabs. the data is separated by a tab stop at every eight characters. what command should you use before processing the data file with the program?

1-45

Answer 41

expand data.txt > data1.txt

Question 42

which of the following commands will change all occurrences of dog in the file animals.txt to mutt in the screen display?

1-45

Answer 42

sed ‘s/dog/mutt/g’ animals.txt

Question 43

you’ve received an ASCII text file (longlines.txt) that uses no carriage returns within paragraphs but two carriages returns between paragraphs. the result is that your preferred text editor displays each paragraph as a very long line. how can you reformat this file so that you can more easily edit it(or a copy)?

1-45

Answer 43

fmt longlines.txt > longlines2.txt

Question 44

which of the following commands will print lines from the file world.txt that contain matches to changes and changed?

1-45

Answer 44

grep change[ds] world.txt

Question 45

which of the following regular expressions will match the strings dog, dug, and various other strings but not dig?

1-45

Answer 45

d[o-u]g