May 10, 2021 05:52 pm GMT
Original Link: https://dev.to/mathlete/cheatsheet-for-the-regex-cheatsheet-part-v-quantifiers-3504
Cheatsheet for the Regex Cheatsheet, Part V: Quantifiers
Intro
I was recently doing a code challenge for a job interview that required me to strip out all nonalphabetic characters. "Ah! I should use Regular Expressions for this!" I thought in triumph, impressed that I even knew what regular expressions were. That fleeting moment of glory faded once I decided to brush up on regular expressions and landed on the encouragingly-named Regular Expressions Cheatsheet. I had no idea how to use it!
So, for people like me, here is a Cheatsheet for the Regular Expressions Cheatsheet, Part V: Quantifiers
What's an Quantifier?
A quantifier finds a sequence of characters to match. It also can be used to find a sequence of expressions to match, but I'm gonna keep it simple here and focus on sequences of characters.
Anatomy of a regular expression
- Forward slashes go on either end like so:
/
something/
- Add
g
for "global" at the end to find every instance, like so:/
something/g
- Add
m
to "multi line" to the beginning/end of each line, not just the beginning/end of each string, like/
something/g
or/
something/gm
Quantifiers
*
0 or more instances of a character
ro*ar
is used in/ro*ar/
to find the following:The lion said roar rooar roooar roooooooar!- Example on regex101.com
- Example in Javascript:
let sentence = "The lion said roar rooar roooar roooooooar!";let regex = /ro*ar/;let found = sentence.match(regex);console.log(found); // [ 'roar', index: 14, input: 'The lion said roar rooar roooar roooooooar!', groups: undefined]
+
1 or more instances of a character
ro+ar
is used in/ro+ar/
to find the following: The lion said roar rooar roooar roooooooar!- Example on regex101.com
- Example in Javascript:
let sentence = "The lion said roar rooar roooar roooooooar!";let regex = /ro+ar/;let found = sentence.match(regex);console.log(found); // [ 'roar', index: 14, input: 'The lion said roar rooar roooar roooooooar!', groups: undefined]
?
0 or 1 instance of a character
ro?ar
is used in/ro+ar/
to find the following: The lion said roar rooar roooar roooooooar!- Example on regex101.com
- Example in Javascript:
let sentence = "The lion said roar rooar roooar roooooooar!";let regex = /ro?ar/;let found = sentence.match(regex);console.log(found); // [ 'roar', index: 14, input: 'The lion said roar rooar roooar roooooooar!', groups: undefined]
{N}
N instances of a character
{3}
is used in/ro{3}ar/
to find the following: The lion said roar rooar roooar roooooooar!- Example on regex101.com
- Example in Javascript:
let sentence = "The lion said roar rooar roooar roooooooar!";let regex = /ro{3}ar/;let found = sentence.match(regex);console.log(found); // [ 'roooar', index: 25, input: 'The lion said roar rooar roooar roooooooar!', groups: undefined]
{N,}
At least N instances of a character
{3,}
is used in/ro{3,}ar/
to find the following: The lion said roar rooar roooar roooooooar!- Example on regex101.com
- Example in Javascript:
let sentence = "The lion said roar rooar roooar roooooooar!";let regex = /ro{3,}ar/;let found = sentence.match(regex);console.log(found); // [ 'roooar', index: 25, input: 'The lion said roar rooar roooar roooooooar!', groups: undefined]
{N,M}
Between N and M instances of a character
{2,4}
is used in/ro{2,4}ar/
to find the following: The lion said roar rooar roooar roooooooar!- Example on regex101.com
- Example in Javascript:
let sentence = "The lion said roar rooar roooar roooooooar!";let regex = /ro{2,4}ar/;let found = sentence.match(regex);console.log(found); // [ 'rooar', index: 19, input: 'The lion said roar rooar roooar roooooooar!', groups: undefined]
Original Link: https://dev.to/mathlete/cheatsheet-for-the-regex-cheatsheet-part-v-quantifiers-3504
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