Lect16 - Advanced String Search

Question 1

Name the basic usage of grep and explain the following parameters:

• -v
• -i
• -b
• -o
• –color
• $

Answer 1

grep <option> <searchpattern> inputfile</searchpattern>
</option>

• -v : reverse grep (show lines that do not match)
• -i : case insensitive
• -b : show a byte offset in the input file to the match
• -o : show only the match
• ^ : match the start of a line
• $ : match the end of a line

Question 2

What are extended regular expression? Explain basic usage?

Answer 2

Extended regular expressions include more metacharacters and include quantifiers that allow for more precise pattern matching.

# grep -E <options> <pattern> inputfile</pattern></options>

oder

# egrep <options> <pattern> inputfile</pattern></options>

Question 3

Explain the following regex sets:

1. match any of the chars a, b, or c
2. match any chars NOT a, b, or c (note inside the brackets)
3. match a range of chars (a through f)
4. any letter
5. any uppercase letter
6. any lowercase letter
7. any whitespace (horizontal)
8. Any digit, 0-9
9. Any alphanumeric character, A-Za-z0-9

Answer 3

1. [abc]
2. [^abc]
3. [a-f]
4. [[:alpha:]]
5. [[:upper:]]
6. [[:lower:]]
7. [[:blank:]]
8. [[:digit:]]
9. [[:alnum:]]

Question 4

Explain the following regex quantifiers:

1. 0 or more of the preceding chars
2. 0 or 1 of the preceding chars
3. 1 or more of the preceding chars
4. Matches any character. e.g.: do? (hit for dog, door, dot, etc)
5. Matches a range of characters: ?ar (matches car, bar or far)
6. the preceding chars match exactly x number of times
7. the preceding chars match at least x, but not more than y times

Answer 4

1. *
2. ?
3. +
4. .
5. []
6. {x}
7. {x,y}

Question 5

Regex examples:

U.S. Phone numbers 516-804-3222

Answer 5

’[[:digit:]]{3}-[[:digit:]]{3}-[[:digit:]]{4}’

or

’([[:digit:]]{3}-){2}-[[:digit:]]{4}’

Question 6

Regex examples:

Matches any words that contains a, b or c

Answer 6

egrep ‘[abc]’ testgr.txt

Question 7

Regex examples:
Matches any words that contains a, b or c once

Answer 7

egrep ‘[abc]{1}’ testgr.txt

Question 8

Regex examples:
Match any line that contains only a, b or c

Answer 8

egrep ‘^[abc]{1}$’ testgr.txt

Question 9

Regex examples:
Matches any line with only alphabetical characters

Answer 9

egrep ‘^[[:alpha:]]*$’ testgr.txt

Question 10

Regex examples:
Matches either “color” or “colour”

Answer 10

egrep ‘colo[u]?r’ testgr.txt

Question 11

Regex examples:
Matches any line with at least 3 numbers

Answer 11

egrep ‘[[:digit:]]{3}’ testgr.txt

Question 12

Regex examples:
Matches either 202-224-1228 or (202)224-1228

Answer 12

egrep ‘(([[:digit:]]{3}))|([[:digit]]{3}-)[[:digit:]]{3}-[[:digit]]{4}’ testgr.txt

Question 13

Regex examples:
Matches ip address

Answer 13

egrep ‘^([[:digit:]]{1,3}.){3}[[:digit:]]{1,3}$’ testgr.txt