Regex Syntax

Question 1

What doesn’t this match /./?

Answer 1

newline characters

Question 2

what does the g flag do?

Answer 2

searches all instances

Question 3

what does the i flag do?

Answer 3

ignores upper and lower case

Question 4

How do you overcome special symbols like ?

Answer 4

backslash to escape
\

Question 5

How to match one of several patterns?
/cat/ and or /dog/

Answer 5

cat|dog|rabbit

pipe operator and brackets

Question 6

Write a regex that matches blueberry or blackberry, but write berry precisely once. Test it with these strings:
blueberry
blackberry
black berry
strawberry

Why does this work?

Answer 6

(blue|black)berry

concatenation works with patterns, not characters. Thus, we can concatenate (blue|black) with berry to produce the final result.

Question 7

Write regex to match all the as, bs or cs in: (2 ways)
Four score + seven

Answer 7

(a|b|c)
[abc]

Question 8

make a regex that will match:
Hoover
hoover
but not match
HooveR
hooveR
(i flag won’t work here)

Answer 8

[hH]hoover

Question 9

Write a regex to match all of the following
a1
a2
a3
b1
b2
b3

Answer 9

[ab][123]

Question 10

how about all the combinations from a-f and 1-9

Answer 10

[a-f][1-9]

Question 11

Match a single character of characters from a-f or x-z

Answer 11

[a-fx-z]

Question 12

Why should you never do this: [A-z]

Answer 12

because there are symbols for other characters in between.
Do this instead:
[A-Za-z]

Question 13

Match all characters EXCEPT the y, a or t

Answer 13

[^yat]

Question 14

Using square brackets, make a regex that will match:
cat, cot, cut, bat, bot, or but

Answer 14

[bc][aou]t

Question 15

Base 20 digits include the decimal digits 0 through 9, and the letters A through J in upper or lowercase. Write a regex that matches base 20 digits. Test it with these strings:
0xDEADBEEF
1234.5678
Jamaica
plow ahead

Answer 15

[0-9a-j]

Question 16

Write a regex that matches any LETTER (not special characters) except x or X. (1 ways) Test it with these strings:
0x1234
Too many XXXXXXXXXXxxxxxxXXXXXXXXXXXX to count.
The quick brown fox jumps over the lazy dog
THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG

Answer 16

[A-WYZa-wyz]

Question 17

Match any character that is not a letter (with and without i):

Answer 17

[^a-z]i
[^a-zA-Z]

Question 18

Are /(ABC|abc)/ and /[Aa][Bb][Cc]/ equivalent regex?

Answer 18

no

Question 19

Are /abc/i and /[Aa][Bb][Cc]/ equivalent regex?

Answer 19

yes

Question 20

write a regex that matches a string that looks like a simple negated character class range, e.g., ‘[^a-z]’. (Your answer should match precisely six characters. The match does not include the slash characters.) Test it with these strings:

The regex /[^a-z]/i matches any character that is
not a letter. Similarly, /[^0-9]/ matches any
non-digit while /[^A-Z]/ matches any character
that is not an uppercase letter. Beware: /[^+-<]/
is at best obscure, and may even be wrong.

Answer 20

[\^[A-Za-z0-9]-[A-Za-z0-9]]

Question 21

What is a character class pattern?

Answer 21

Character class patterns use a list of characters between square brackets, e.g., /[abc]/. Such a pattern matches a single occurrence of any of the characters between the brackets. Try these regex:

Question 22

Match any character (except newline characters)

Answer 22

/./

Question 23

Match any whitespace character (using class shortcut):
space (‘ ‘), tab (‘\t’), vertical tab (‘\v’), carriage return (‘\r’), line feed (‘\n’), and form feed (‘\f’),

Match any non-whitespace character (the others)

Answer 23

/s
/S

Question 24

match numbers 0-9 (using class shortcut)

match any non-digit character
(using class shortcut)

Answer 24

\d

\D

Question 25

Match word characters a-z i 0-9 Match nonword characters

Answer 25

\w \W

Question 26

Write a regex that matches any sequence of three characters delimited by whitespace characters (the regex should match both the delimiting whitespace and the sequence of 3 characters). Test it with these strings: reds and blues the lazy cat sleeps

Answer 26

\s...\s

Question 27

\s...\s on Doc in a big red box. Hup! 2 3 4 will not match red. Why not?

Answer 27

doesn't match since the regex engine consumes the space character that precedes red when it matches big (note the trailing space). Once consumed as part of a match, the character is no longer available for subsequent matches.

Question 28

Write a regex that matches any four digit hexadecimal number that is both preceded and followed by whitespace. Note that 0x1234 is not a hexadecimal number in this exercise: there is no space before the number 1234. Hello 4567 bye CDEF - cdef 0x1234 0x5678 0xABCD 1F8A done 2 matches

Answer 28

/\s[\dA-F][\dA-F][\dA-F][\dA-F]\s/ig

Question 29

Write a regex that matches any sequence of three letters. Test it with these strings:

Answer 29

(there are no class shortcuts for just letters) /[a-z][a-z][a-z]/i

Question 30

Write regex to target 'cat' at the beginning, end of a string, or beginning and end of a string cat blah blah blah blah cat

Answer 30

^cat cat$ ^cat$

Question 31

Write regex to match 3 characterse of strings or numbers using word bound anchors One fish, Two fish, Red fish, Blue fish. 123 456 7890

Answer 31

\b\w\w\w\b

Question 32

Match the first 3 characters of a word Match the last 3

Answer 32

/\b\w\w\w \w\w\w\b/

Question 33

match the john in abcjohnabc doejohn but not the john in johnson

Answer 33

\Bjohn

Question 34

Write a regex that matches the word The when it occurs at the beginning of a line. Test it with these strings: The lazy cat sleeps. The number 623 is not a word. Then, we went to the movies. Ah. The bus has arrived.

Answer 34

^the\b need the \b to make sure it's just the word the and not then

Question 35

Write a regex to get cat in: The number 623 is not a cat but not: The lazy cat sleeps The Alaskan drives a snowcat

Answer 35

\bcat$ need the \b to make sure it's just the word cat and not scat or snowcat

Question 36

Write a regex that matches any three-letter word; a word is any string comprised entirely of letters. You can use these test strings. reds and blues The lazy cat sleeps. The number 623 is not a word. Or is it?

Answer 36

b[a-z][a-z][a-z]\b

Question 37

Write a regex that matches an entire line of text that consists of exactly 3 words as follows: The first word is A or The. There is a single space between the first and second words. The second word is any 4-letter word. There is a single space between the second and third words. The third word -- the last word -- is either dog or cat. Test your solution with these strings: A grey cat A blue caterpillar The lazy dog The white cat A loud dog --A loud dog Go away dog The ugly rat The lazy, loud dog

Answer 37

(^(a|the) [a-z][a-z][a-z][a-z] (dog|cat)$)

Question 38

Write a regex that matches an entire line of text that consists of exactly 3 words as follows: The first word is A or The. There is a single space between the first and second words. The second word is any 4-letter word. There is a single space between the second and third words. The third word -- the last word -- is either dog or cat. Test your solution with these strings: A grey cat A blue caterpillar The lazy dog The white cat A loud dog --A loud dog Go away dog The ugly rat The lazy, loud dog

Answer 38

(^(a|the) [a-z][a-z][a-z][a-z] (dog|cat)$)

Question 39

What's the difference between a non-whitespace character and a word character

Answer 39

non-whitespace character includes symbols word character is just a-z 0-9

Question 40

Write a regex to match 3 or more digits limited as a word

Answer 40

\b/d/d/d/d*\b the /d* doesn't mean 4 digits, it means "more digits if needed" "Zero or more additional digits"

Question 41

what happens if you have x* with no words bounds?

Answer 41

Because it matches "0 or more of x" it will max 0. Like empty strings.

Question 42

What will this match /co*t/? ct cot coot cooot

Answer 42

All

Question 43

Which of these will this match? \b\d\d\d\d+ 123 1234 12345 12 1

Answer 43

4 or more

Question 43

What will this match: 1(234)*5 of these? 15 12345 12342342345 1234235

Answer 43

Top 3

Question 44

So what does \d+ match? compared to \d*

Answer 44

1 or more 0 or more

Question 45

Which of these will this match? coo?t ct cot coot cooot

Answer 45

cot or coot

Question 46

what does /x?/ match

Answer 46

either x or nothingness

Question 47

Write a regex to match 20170111 or 2017-01-11

Answer 47

\b\d\d\d\d-?\d\d-?\d\d\b

Question 48

Write a regex to match 20170111 or 2017-01-11 or 2015/02/12

Answer 48

The answer given was \d\d\d\d(-?|/?)\d\d(-?|/?)\d\d I think (-|/)? is better. Because (-?|/) would do it. - or '', or /

Question 49

will a? match an empty string like a*?

Answer 49

yes

Question 50

What will this match: asd{2} of asdasdasdasd

Answer 50

Nothing it's looking for as and then 2 ds asdd

Question 51

write a regex to match 10 digits (but not 9 or 11)

Answer 51

\d{10}

Question 52

write a regex to match 10 or more digits

Answer 52

\d{10,}

Question 53

write a regex to match 10 to 13 digits

Answer 53

\d{10,13}

Question 54

write a regex to match 5-8 letter words

Answer 54

\b[a-zA-Z]{5,8}\b

Question 55

What will this match: a[abc]*c of this: xabcbcbacy

Answer 55

abcbcbac The longest thing it can. It's greedy.

Question 56

Make a[abc]*c Not match the longest thing it can

Answer 56

a[abc]*?c Question mark on the main quantifier

Question 57

Write a regex that matches any word that begins with b and ends with an e, and has any number of letters in-between. You may limit your regex to lowercase letters. Test it with these strings. To be or not to be Be a busy bee I brake for animals.

Answer 57

\bb[a-z]*e\b

Question 58

Write a regex that matches any LINE (the whole line, the whole line, the whole line) of text that ends with a ?. Test it with these strings. Then make one that doesn't match a line that is only a ? What's up, doc? Say what? No way. ? Who? What? Where? When? How?

Answer 58

^.*\?$ Then ^.{1,}\?$ or ^.+\?$

Question 59

Write a regex that matches any line of text that contains nothing but a URL. For this exercise, a URL begins with http:// or https://, and continues until it detects a whitespace character or end of line. Test your regex with these strings: http://launchschool.com/ https://mail.google.com/mail/u/0/#inbox htpps://example.com Go to http://launchschool.com/ https://user.example.com/test.cgi?a=p&c=0&t=0&g=0 hello http://launchschool.com/ Then modify to allow whitespace before and after. Then so that it can appear anywhere (as long as it's word bound)

Answer 59

^https?:\/\/\S*$ ^https?:\/\/\S*$ \bhttps?:\/\/\S*\b

Question 60

Write a regex that matches any word that contains at least three occurrences of the letter i. Test your regex against these strings: Mississippi ziti 0minimize7 inviting illegal iridium

Answer 60

\b([a-z]*i){3,}[a-z]*\b gi

Question 61

Write a regex that matches the last word in each line of text. For this exercise, assume that words are any sequence of non-whitespace characters. Test your regex against these strings: What's up, doc? I tawt I taw a putty tat! Thufferin' thuccotath! Oh my darling, Clementine! Camptown ladies sing this song, doo dah.

Answer 61

\b\S+$

Question 62

Write a regex that matches lines of text that contain at least 3, but no more than 6, consecutive comma separated numbers. You may assume that every number on each line is both preceded by and followed by a comma. Test your regex against these strings: ,123,456,789,123,345, ,123,456,,789,123, ,23,56,7, ,13,45,78,23,45,34, ,13,45,78,23,45,34,56,

Answer 62

^,(\d+,){3,6}$

Question 63

Write a regex that matches lines of text that contain at least 3, but no more than 6, consecutive comma separated numbers. In this exercise, you can assume that the first number on each line is not preceded by a comma, and the last number is not followed by a comma. Test your regex against these strings: 123,456,789,123,345 123,456,,789,123 23,56,7 13,45,78,23,45,34 13,45,78,23,45,34,56

Answer 63

/^(\d+,){2,5}\d+$/

Question 64

Write a regex that matches lines of text that contain either 3 comma separated numbers or 6 or more comma separated numbers. Test your regex against these strings: ( 2 ways, 1 version without pipe operator) 123,456,789,123,345 123,456,,789,123 23,56,7 13,45,78,23,45,34 13,45,78,23,45,34,56

Answer 64

(^(\d+,){2}\d+$|^(\d+,){5,}\d+$) or ^(\d+,){2}((\d+,){3,})?\d+$

Question 65

Write a regex that matches HTML h1 header tags, e.g.,

Main Heading

Another Main Heading

ABC

Paragraph

DEF

Done

(Copy it from here:) https://launchschool.com/books/regex/read/quantifiers#greediness

Answer 65

.*?

Question 66

Broad category name for these thigns: +*?{}

Answer 66

quantifier

Question 67

what will this match: [a-z]*i of aiz iz aaaizzzi

Answer 67

ai i aaaizzzi