regex, sed, gawk, quiz 2

Question 1

what is a regular expression

Answer 1

a description of a pattern of text

Question 2

regex quantifier *

Answer 2

zero or more of the preceding characters

Question 3

regex quantifier +

Answer 3

one or more of the preceding characters

Question 4

regex quantifier ?

Answer 4

zero or one of the preceding characters

Question 5

regex quantifier {min, max}

Answer 5

between min and max of preceding characters

Question 6

regex character set [ ]

Answer 6

any single character in grouped set

Question 7

regex character set [char - char]

Answer 7

any single enclosed range of characters, such as a-z, A-Z, 0-9

Question 8

regex character set [^]

Answer 8

complement, excluding the enclosed character, a single character not in a grouped set. For example [^abcd] will match any character that isn’t a, b, c, or d.

Question 9

[[:alpha:]]

Answer 9

alphabetic characters, [a-zA-Z]
used in regex

Question 10

[[:lower:]]

Answer 10

lower case alphabetic characters, [a-z]
used in regex

Question 11

[[:upper:]]

Answer 11

upper case alphabetic characters, [A-Z]
used in regex

Question 12

[[:digit:]]

Answer 12

digits, [0-9]
used by regex

Question 13

[[:alnum:]]

Answer 13

alphanumeric, [a-zA-Z0-9]
used in regex

Question 14

[[:punct:]]

Answer 14

punctuation and symbols
used by regex

Question 15

[[:space:]]

Answer 15

whitespace (e.g., newline, space, tab)
used in regex

Question 16

regex anchor ^

Answer 16

beginning of the line

Question 17

regex anchor $

Answer 17

end of the line

Question 18

regex anchor <

Answer 18

beginning of word

Question 19

regex anchor >

Answer 19

end of word

Question 20

regex special character .

Answer 20

any single character, except newline

Question 21

regex special character \

Answer 21

escape sequence, escapes the character following it

Question 22

regex special character |

Answer 22

logical OR grouping

Question 23

regex special character ()

Answer 23

group character set

Question 24

grep

Answer 24

standard version of grep that supports basic regular expressions

Question 25

egrep (grep –E)

Answer 25

Extended grep that understands extended regexes

Question 26

fgrep (grep –F)

Answer 26

Supports fixed strings for faster performance

Question 27

rgrep (grep –R)

Answer 27

Traverses subdirectories recursively

Question 28

grep option -c

Answer 28

print only a count of matched lines

Question 29

grep option -i

Answer 29

ignore uppercase and lowercase distinctions

Question 30

grep option -l

Answer 30

list all files that contain the specified pattern

Question 31

grep option -n

Answer 31

print matched lines and line numbers

Question 32

grep option -s

Answer 32

work silently – display nothing except error messages

Question 33

grep option -v

Answer 33

print lines that do not match the pattern

Question 34

sed option -r

Answer 34

makes regexes work better

Question 35

sed option -n

Answer 35

only prints lines specified with print command

Question 36

sed option -f

Answer 36

next argument is the filename containing editing commands

Question 37

sed option -e

Answer 37

next argument is an editing command rather than a filename, useful if multiple commands are specified

Question 38

sed command d

Answer 38

deletes all lines, can be modified such as 6d to delete line 6 or 1,10d to delete line 1 through 10

Question 39

sed command s

Answer 39

substitute, s/regex/new/

Question 40

sed command a

Answer 40

append

Question 41

sed command i

Answer 41

insert

Question 42

sed command c

Answer 42

change

Question 43

sed command p

Answer 43

print:
Print command (p) used to force pattern space to be output,
useful if -n option has been specified

Question 44

sed command r

Answer 44

read

Question 45

sed command w

Answer 45

write

Question 46

sed command y

Answer 46

transform

Question 47

sed command =

Answer 47

display line number, Line number command (=) writes the current line number before each matched/output line

Question 48

sed command N

Answer 48

append next line to current one

Question 49

sed command q

Answer 49

quit, Syntax: [addr]q – Quit (exit sed) when addr is encountered
To print the first 100 lines of a file (like head)
sed ‘100q’ filename

Question 50

sed flag n

Answer 50

a number from 1 to 512 indicating which occurrence of pattern
should be replaced

Question 51

sed flag g

Answer 51

global, replace all occurrences of pattern in pattern space

Question 52

sed flag p

Answer 52

print contents of pattern space

Question 53

what is gawk

Answer 53

A scripting language used for manipulating data and generating reports
– Geared towards working with delimited fields on a line-by-line basis

Question 54

gawk system variable FS

Answer 54

Field separator (default = space), left to right

Question 55

gawk system variable RS

Answer 55

Record separator (default = \n), top to bottom

Question 56

gawk system variable NF

Answer 56

Number of fields in current record

Question 57

gawk system variable NR

Answer 57

Number of the current record

Question 58

gawk system variable OFS

Answer 58

Output field separator (default = space)

Question 59

gawk system variable ORS

Answer 59

Output record separator (default = \n)

Question 60

gawk system variable FILENAME

Answer 60

current filename

Question 61

gawk system variable ARGC/ARGV

Answer 61

Get arguments from command line

Question 62

Which sed command is used to read and insert the contents of a file at the current position in the output?

Answer 62

r

Question 63

Which regex metacharacter is used to specify the end of a line?

Answer 63

’$’

Question 64

What does the regex (abc|def) match?

Answer 64

Either “abc” or “def”.

Question 65

Which regex quantifier is used to match one or more occurrences of the preceding element?

Answer 65

’+’

Question 66

In regex, the . (dot) character typically represents _______________

Answer 66

Any single character except a newline.

Question 67

You have a log file and want to find all lines that start with the word “ERROR” followed by a colon. Which grep command would you use?

Answer 67

grep “^ERROR:” logfile.txt

Question 68

You want to count the number of lines in a file that do not contain the word “error.” Which grep command would you use?

Answer 68

grep -c -v “error” file.txt

Question 69

How can you make sed edit a file in place (i.e., modify the file directly)?

Answer 69

Use -i option

Question 70

sed option -i

Answer 70

modifies the file in place, basically saves the substitutions

Question 71

What is the purpose of the -n option in sed?

Answer 71

Suppresses automatic printing of pattern space.

Question 72

How can you specify a range of lines to apply a sed command to?

Answer 72

single line numbers separated by a comma (e.g., 1,3).

Question 73

(True / False) The command below replaces the 5th line of a file with a new line of text

sed ‘5s/.*/This is a new line/’ input.txt > output.txt

Answer 73

True

Question 74

(True / False) The command below remove all non-empty lines from a file

sed ‘/^$/d’ input.txt > output.txt

Answer 74

False

Question 75

Match the regex with the right hand side

^+\d{1,3}-\d{3}-\d{3}-\d{4}$

(https?|ftp)://[^\s/$.?#].[^\s]*

(\d{1,3}.){3}\d{1,3}

Answer 75

+1 555-555-5555

https://linkedin.com

Matches IPv4 addresses such as 192.168.1.1