1)What is Regular expressions?
-Regular expressions is used to perform powerful and efficient text processing
-It is simple like search editors and powerful text processing language
-This is powerful pattern language
-Matching performed based on the bit pattern used for the encoding the character not based graphic representation of the character
-Regualr expressions composed with two types of characters
1)meta characters (like *)
2)litrals
2)How many types of Regex engines available ?
two types
1)DFA
2)NFA
3)What are good regex concerns (or) principles?
1)Understanding the requirement properly
2)Matching what you want
3)Keeping the Regex manageable and understandable
4)What is Anchors in Regular expressions?
Go to search type *.txt
meaning of pattern is to select all the files which has extension .txt
13)What is Backreferencing in Regular expressions?
Backreferencing is a feature of regular expressions, it is used to match new text that is same as matched earlier in the expression.
[0-9]+ match all the digits 9334
([0-9])\1+ match only 9334
\1 represent the match which was matched ([0-9])
14)What is lookaround in Regular expressions?
Generally regex works left to right but sometimes needs to process the text right to left.
Processing text right to left is called lookaround.
example : Needs to insert coma after three digits in cash
12,345,678
15)How lookaround works in Regular expressions?
It is working like meta characters [\b][^][$] but they match the text based on positions with in the text.
16)Types of lookaround in Regular expressions?
we have two types of look around.
1) lookahead
2)lookbehind
17)What is lookahead in Regular expressions?
It is working towords to the right to see if match is exist
Positive Lookahead:
If successful match to the right
positive lookahead is specified with ( ?=...)
Ex: (?=\d) successful where digit comes right
Negative Lookahead:
If successful not match to the right
positive lookahead is specified with ( ?!=...)
18)What is lookbehind in Regular expressions?
It is working towords to the left to see if match is exist
Positive Lookbehind:
If match is successful match to the left
Positive lookbehind is specified with ( ?<=...)
Ex: (?<=\d) successful where digit comes left
Negative Lookbehind:
If match is successful not match to the left
Negative lookbehind is specified with ( ?<!...)
19)What is the meaning "(?" in Regula expressions?
Open parenthesis sequence , They all begin with two characters like (? always perform some special functionality
(?: ..) : group it but don't capture
(?=...): look ahead
(?<=...) : look behind
20)What is meta character represent the space in Regular expressions?
\s - is used represent the space
\s* - represent more than one whitespace.
Shiva\s*Gummadidala
Shiva Gummadidala
21) What is escape sequence character in Regex?
'\' character represent escape sequence.
Want to match any character which is having special meaning then we use escape sequence character.
a\^b will match a^b
22) What is regular expression flags ?
Ragular expression flags sometimes called as modifiers , they are effect the way of pattren matching.
Different kinds of flags available
/g,/i etc.
23)What is meta character in Regular expressions?
Meta characters used to form syntax of regular expressions.
Ex: ^, .,& etc..
24) Can we give regular expression range in descending order like [20-10] ?
No , we shouldn't give , if you give will out of range expression error.
25)What is CapturingGroup Regular expressions?
-if you feel portion of the regex using later part of the regex then we use capturing groups.
-its represent with meta characters inside parenthesis and its repetitions represented with \1 , \2 etc..
- its also called as Backreferencing
(abcd)(efgh) \1\2 will match abcdefghabcdefgh
26)What is NonCapturingGroup Regular expressions?
if you want to make capturing group as non NonCapturingGroup use ?:.
(?:abcd) is NonCapturingGroup - can not use this group later.
27) What is the difference between ([PQR]+) and ([PQR])+?
Both are matching PQR ,
-([PQR]+) put PQR saved in first back reference.
-([PQR])+ , first time P was saved , second time Q was saved and third time R was saved. + causes the pair of parenthesis to repeat three times.
28) What is the namespace represented the Regular expressions in C#.NET?
System.Text.RegularExpressions.Regex.
29) What is character class subtraction in Regular expressions?
Want to exclude set of character from matched text then use character class subtraction.
syntax : [Base_group -[Exclude_group]]
[0-5-[23]]
given input data array is {"12","145",""1054}
output is array is {"145",""1054} 2 excluded so that "12" not getting selected.
30) What is Name matched sub expressions in Regular expressions?
Matched string captured by sub expression by using name. Let you access this it by name or number
syntax : (?<givne_name> subexpression)
Ex : (?<Given_Name> \w+) -> Capturing method syntax
Console.WriteLine(Match.Goups["given_name"].value);
31)What is conditional matching in Regex?
-Using conditional matching match the text from one of two given patterns.
(?(capturinggroup) pattern1/pattern2)
((?<n2>\d{2}-)\b\d{2}\b | \b\d{4}\b)
12-222-9999
32)What is Zero width assertions in Regular expressions?
These are using for matching the position rather than text the line.
\A - Matching the starting of the line.
\Z - Matching the end of the line. Etc
For Regular expressions core concepts click here
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