FAQ: Introduction to Regular Expressions - Character Sets

This community-built FAQ covers the “Character Sets” exercise from the lesson “Introduction to Regular Expressions”.

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This exercise can be found in the following Codecademy content:

Practical Data Cleaning

FAQs on the exercise Character Sets

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Can we use carrot symbol in the middle of character set like [c^at]?

matching the character ‘c’ but not ‘a’ and ‘t’

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then you can simple use [c], not it will only match c and not a or t (or any other symbol/letter)

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What if we want to match a word containing ‘c’ but not ‘a’ or ‘t’?

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 > regex = /[c][^at]/g
<- /[c][^at]/g
 > regex.test('actor')
<- false
 > regex.test('chore')
<- true

The above is actually JavaScript, but the pattern would apply in any language.

Note how the NOT character is applied inside the class, [^at].


what would ^[cat] do?

It would serve you better to just google regular expression and find a decent page on the subject.



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FTR, The pattern looks for a first letter that is either a ‘c’, an ‘a’ or a ‘t’ or any combination of the three.

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can you tell me what bc^[cat] does? I understand that ^[cat] will match if any line start with either c or a or t. Also, i understand that ^[cat]bc will match any line starting with either cbc or abc or tbc. I guess bc^[cat] isn’t a valid regex, am I correct…?

Asserts position at start of line, so cannot have anything before it.

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