1. What are regular expressions? What are they used for? (each 10 points) 2. Ass

Question

1. What are regular expressions? What are they used for? (each 10 points)

2. Assume you have a file that contains these lines:

a3b

adcbcbc

12c5a36

a5

3c

1) In the above file which line(s) will match the regular expression of '[a3][5c]' ? (10 points)

2) In the above file which lines will the regular expression of '^.3.*b' match? (10 points)

3. Explain what this regular expression will match: (10 points)

   abcd{5}

4. Write a grep command that get a list of files that contain the string zip preceded by any character except b or g. (10 points)

5. Given a file containing the lines at the right, list which lines will be matched by each of the following egrep patterns: (each 5 points)

cat
catch
cart
crepe
oxcart
encarta
fire
fireplace
family
fame

1. '^c'

2. 'e$'

3. '^....$'

4. 'c.r'

5. 't.$'

6. 't.?$'

7. 't.+$'

8. 't.*$'

9. '^.[ai]'

10. '^.[^ai]'

1. What does the following awk command do and output? (20 points)

     awk  

Explanation / Answer

1. Set of chars that repeats itself in the form of pattern

2a. a5, 3c [grep '[a3][5c]' file]

2b. a3b [grep '^.3.*b']

3. It searches for abcd{5}. [here is escape char]

4. ls -f1|grep '.*[^b^g].zip'

5.1. cat catch cart crepe - [begins with c]

5.2. creppe fire fireplace fame - [ends with e]

5.3. cat - [contains only 3 char]

5.4. cart oxcart encarta - [words containing 3 alphabets with c as start and t as end]

5.5. encarta - [ends with t and some char]

5.6. cat cart oxcart encarta - [ends with t or t with one more char]

5.7. catch encarta - [t with any no of chars after t]

5.8. cat catch cart oxcart encarta [ends with t or t followed by any no of char]

5.9. fire fireplace family fame - [second char is a or i]

5.10. cat catch cart crepe oxcart encarta - [second char is not a or i]

1. Prints the number of lines which are null [or] "".

2. sed -e 's/.{80}/&;/g' prg

3. sed -n '1,10p' file

4. grep '^[^.]+::' /etc/passwd | awk 'BEGIN {print $1}'

5. awk '{print NR " " $1}' file

6. sed -e 's/^#//g' prg

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