103.7 Search text files using regular expressions

Question 1

What command do you usually use with regular expressions?

Answer 1

grep

Question 2

What does a dot (.) represent in a regex?

Answer 2

A dot represents a single character. More than one dot can be used consecutively to represent more unknown characters in a row.

Question 3

What symbol do you use to search for a string at the beginning of a line and at the end of a line in a regex?

Answer 3

At the beginning: ^

At the end: $

Question 4

What syntax would you use to search for a line that contains a specified character using a regex?

Answer 4

grep [x]

Question 5

What syntax would you use to search for a line that contains a string at the end using a regex?

Answer 5

grep bash$

Question 6

What syntax would you use to search for a line that contains a string the beginning using a regex?

Answer 6

grep ^rpc

Question 7

What syntax would you use to search for a line that contains either a capital or a lowercase character using a regex?

Answer 7

#grep -i [x] 
#grep [Xx]

Question 8

What syntax would you use to search for a line in a file that begins with either a capital or lowercase A, then followed by any character and the third character being either a capital or lowercase A?

Answer 8

#grep ^[Aa] .[Aa] 
$grep -i ^[a].[a]

Question 9

What symbols do you use to exclude a character from a search in a regex?

Answer 9

[^abc]

Question 10

What does the star sign mean in a regex?

Answer 10

It matches zero or more of the preceding characters or expression.

Question 11

What does the #egrep command do?

Answer 11

It searches a specified file line by line returning lines that contain a pattern matching a given regular expression.

Question 12

What is the equivalent of egrep?

Answer 12

grep -E

Question 13

How do you egrep a file for lines that contain {bash} at the end of the lines?

Answer 13

egrep ‘bash$’

Question 14

How do you egrep a file just to know how many lines contain the string at the end of the lines?

Answer 14

egrep -c ‘bash$’

Question 15

How do you egrep a file to find lines that contain a string at the beginning or another string at the end of the lines?

Answer 15

egrep ‘^rpc|nologin$’

Question 16

What does the fgrep command do?

Answer 16

It searches based on strings rather than patterns. Also uses file globbing instead of regexes.
It equals to grep -F

Question 17

What is the syntax for the #sed command to replace a string for another globally in a whole document?

Answer 17

sed ‘s/orignalstring/newstring/g’

Question 18

In the #sed command, what flag do you use to make the stream search case insensitive? What flag do you use to prevent another file being created?

Answer 18

#sed -I (case insensitive)
#sed -i (in place)

Question 19

What is the syntax for the #sed command to make a change permanent in a file?

Answer 19

sed -i ‘s/orignalstring/newstring/g’

Question 20

What is the syntax for the #sed command?

Answer 20

sed ‘s/orignalstring/newstring/’

Question 21

What is the command that is usually used to search and replace words in a file?

Answer 21

sed