Linux: grep command

Question 1

dot (‘ . ‘)

Answer 1

Matches 1 of any character

grep “c.t” dictionary

wildcat
yacht
woodcutter

grep ^c.t$ dictionary
cat
cut

Question 2

Literal string

Answer 2

grep ^the word$ dictionary

Question 3

Classes

Answer 3

a defined class of characters, whether individual or a range

[a-c]at = acrobat
[0-9][0-9]  = 99 ,13

Question 4

Find all lowercase letters and numbers USING classes

Answer 4

[a-z0-9]

Question 5

Character classes

Answer 5

[[:alpha:]] = [a-zA-Z]
[[:upper:]] = [A-Z]
[[:lower:]] = [a-z]
[[:digit:]] = [0-9]
[[:alnum:]] = [0-9a-zA-Z]
[[:space:]]  matches any whitespace, including tabs

Question 6

Character class abbreviations

Answer 6

\d  = [[:digit:]] 
\w = [[:alnum:]] 
\s  = [[:space:]] 

\D = [^0-9]
\W = [^a-z....]
\S = [^\t\n\r\f]