Question

UNIX and Shell Programming.

Given the regular expression, circle all the matching patterns.

Problem 1. \..\{3\}$

a. rs.ef$tt

b. abc.ab

c. abc.$$$$

d. abc

e. none

Problem 2: :?.?

a. :a?????????

b. eeeeeefffff?hhhh

c. aaa::??????

d. :?.\?

e. none

Problem 3.   Write a regular expression that matches a nonblank line.

Answer 1

Please find the following match for regular expressions.

Problem 1. \..\{3\}$

The above regular expression matches pattern ends with "." and any same character occurrence of three.

Answer: none

//its not matching any of the patterns

USER> grep '\..\{3\}$' reg1

Problem 2: :?.?

The above regular expression matches a pattern with":<any character><any character><any character>"

Answer: aaa::??????

USER> grep ':?.?' reg2
aaa::??????

Program 3:

This regular expression -e '^[[:space:]]*$' matches only blank line or  lines with spaces/tabs, if we add "-v' to grep then, it will display only the non blank lines

USER> cat reg2
:a?????????
eeeeeefffff?hhhh

aaa::??????

:?.\?

USER> grep -v -e '^[[:space:]]*$' reg2
:a?????????
eeeeeefffff?hhhh
aaa::??????
:?.\?