Grep & RegExp

Question 1

To find lines in test.txt that have word “seven”

So if you have lines
line 1: five seventeen two
line 2: five seven two

only “five seven two “ will be found

Answer 1

grep -w ‘seven’ test.txt

Question 2

To find lines in test.txt where we have words that start with “seven”

Answer 2

grep ‘\

Question 3

To find in file test.txt lines where we have words that ends with seven, like ‘seven’ not ‘seventeen’

Answer 3

grep ‘seven>’ test.txt

Question 4

To find in test.txt file lines which start with seven. So

will be found: ‘seven five two’
but
won’t be found: ‘five seven two’

Answer 4

grep ‘^seven’ test.txt

Question 5

To find in test.txt file lines which end with seven. So

five two seven - will be found
but
five seven two - won’t be found

Answer 5

grep ‘seven$’ test.txt

Question 6

For file test.txt

1. To show one line before and one row after the grep pattern in the file test.txt like
   #line UP
   twentyseven
   #line down
2. To show one row before grep pattern
   #line UP
   twentyseven
3. To show one row after grep pattern
   twentyseven
   #line down

Answer 6

1. before and after: grep -C 1 twentyseven test.txt
2. after match: grep -B 1 twentyseven test.txt
3. before match: grep -A 1 twentyseven test.txt

Question 7

To show lines where twenty1, twenty2, twenty3, twenty4 exist

for

twenty1
twenty3
twenty5
twenty7

Answer 7

grep “twenty[1-4]” test.txt

Question 8

To exclude lines where twenty1, twenty2, twenty3, twenty4 exist

for

twenty1
twenty3
twenty5
twenty7

Answer 8

grep “twenty[^1-4]” test.txt

Question 9

nameserver 127.0.0.1

For file test.txt

nameserver 8.8.8.8
nameserver 77.88.8.8
nameserver 8.8.4.4

show lines with ip and exlude lines which are comments - have # at the begining

Answer 9

grep -E ‘\b[0-9]{1,3}(.[0-9]{1,3}){3}\b’ /etc/resolv.conf | grep -v ‘#’

will show
nameserver 8.8.8.8
nameserver 77.88.8.8
nameserver 8.8.4.4

and wont show 
#nameserver 127.0.0.1

Question 10

For file test.txt
#nameserver 127.0.0.1
nameserver 8.8.8.8
nameserver 77.88.8.8
nameserver 8.8.4.4

to show only ip excluding line with a comment (line starts with #)
Will be shown
8.8.8.8
77.88.8.8
8.8.4.4

not
127.0.0.1

Answer 10

grep -v ‘#’ /etc/resolv.conf | grep ‘\b[0-9]{1,3}(.[0-9]{1,3}){3}\b’

Question 11

Case insensitive search of grep_pattern using grep in file test.txt

Answer 11

grep -i grep_pattern file_pattern test.txt

Question 12

A regular expression matches any single character

Answer 12

the sign “.”

e. g.
text. *text
text. text

Question 13

Specify the color parameter in a grep-specific environment variable

Answer 13

$ export GREP_OPTIONS=’–color=auto’ GREP_COLOR=’100;8’

Question 14

Searching in all files recursively using grep. When you want to search in all the files under the current directory and its sub directory

Answer 14

grep -r “ramesh” *

Question 15

Invert match using grep (exclude pattern from the search)

Answer 15

grep -v “go” demo_text

Question 16

To count that how many lines matches the given pattern/string

Answer 16

grep -c “pattern” filename

Question 17

Show only the matched string in demo_file that contains is line

like

is line is the 1st lower case line
is line
is is the last line

Answer 17

grep -o “is.*line” demo_file

Question 18

A regular expression matches any single character - that is optional and will be matched at most once

Answer 18

‘?’

Question 19

A regular expression matches any single character - that will be matched zero or more times.

Answer 19

‘*’

Question 20

A regular expression matches any single character - that item will be matched one or more times

Answer 20

’+’

Question 21

A regular expression matches any single character the preceding item is matched exactly n times

Answer 21

‘{n}’

Question 22

A regular expression matches any single character is matched n or more times

Answer 22

‘{n,}’

Question 23

A regular expression matches item is matched at most m times. This is a GNU extension

Answer 23

‘{,m}’

Question 24

A regular expression matches any single character is matched at least n times, but not more than m times

Answer 24

‘{n,m}’

Question 25

To show the line number of file with the line matched like

Answer 25

grep -n “go” demo_text

Question 26

With this option grep won’t show strings with that result but reports file names where this pattern was found.

E.g. for word Alice in current folder

Answer 26

grep -l ‘Alice’ ./*

Question 27

Сообщает имена тех файлов, где не встретился ОБРАЗЕЦ:

Answer 27

grep -L ‘Алиса’ example/*

Question 28

What is the difference in using

a*
a+
a?

Answer 28

a* -> 0 or more
a+ -> 1 or more
a? ->0 or 1

Question 29

What is the difference in using

a{5}
a{2,}
a{1,3}

Answer 29

a{5} ->exactly five,
a{2,} ->two or more
a{1,3} ->between one & three

Question 30

What does ab|cd mean

Answer 30

Match ab or cd

Question 31

What do mean

```
abc
\1
(?:abc)
(?=abc)
(?!abc)
~~~

Answer 31

(abc)	capture group
\1	        backreference to group #1
(?:abc)	non-capturing group
(?=abc)	positive lookahead
(?!abc)	negative lookahead

Question 32

\w
\d 
\s	 
\W 
\D 
\S

Answer 32

\w  word
\d   digit
\s    whitespace
\W  not word
\D   digit
\S   whitespace

Question 33

To find 4 letter words in

drink beer, it’s very nice!

so “beer”, “very”, “nice” are found

Answer 33

\b\w{4}\b