Regular expression to match first and last character

Question

I'm trying to use regex to check that the first and last characters in a string are alpha characters between a-z.

I know this matches the first character:

/^[a-z]/i

But how do I then check for the last character as well?

This:

/^[a-z][a-z]$/i

does not work. And I suspect there should be something in between the two clauses, but I don't know what!

Laurasia

Answer 1

The below regex will match the strings that start and end with an alpha character.

/^[a-z].*[a-z]$/igm

The a string also starts and ends with an alpha character, right? Then you have to use the below regex.

/^[a-z](.*[a-z])?$/igm

DEMO

Explanation:

^             #  Represents beginning of a line
[a-z]         #  Alphabetic character
.*            #  Any character 0 or more times
[a-z]         #  Alphabetic character
$             #  End of a line
i             #  Case-insensitive match
g             #  Global
m             #  Multiline

Gilroy

Lookahead is completely unnecessary here. – Hinz

This is completely identical to the other answer. – Geographical

he misses the g modifier. – Gilroy

Why do you need g modifier? – Solidstate

@M42 g modifier: global. All matches (don't return on first match) – Gilroy

Sure, but it has nothing to do here because we match the whole string. – Solidstate

without g modifier, it fails to match the string in the second line.regex101.com/r/jO2pI2 – Gilroy

Kudos to you for explaining that sh**! :) – Lali

@AvinashRaj, what should I do to make the first character== last character in your regex. – Crotch

Answer 2

You can do it as follows to check for the first and last characters and then anything in between:

/^[a-z].*[a-z]$/im

DEMO

Wobbly

The flag m would help as well. – Gerstner

@hjpotter92, Thank you. I have included it in my answer – Wobbly

@Wobbly .* would have done instead of .*?. Backtracking will be better because of anchor. – Geographical

@Unihedron, Thank you. I have changed my answer. I guess I just feel safer with .*? – Wobbly

Answer 3

You can use this:

/^.|.$/gim

it matches with first and last character

Neile

Answer 4

 var str = "Regular";
//following code should return true as first and last characters are same
var re = /(^[a-zA-Z])(.*)\1$/gi;

console.log(re.test(str); //true

Match 1 : Regular
Group 1 : (^[a-zA-Z]) = R
Group 2 : (.*) = egula
\1$ : Match the same what is caught in group 1 at the end = r

Jinnyjinrikisha

That is not was asked. – Solidstate

Answer 5

put characters in groups like ([group1])([group2])\1. The \1 says the last group matches group 1.

([a-z])([someRegex])\1

Westerly