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!

score 57 · Accepted Answer · edited Jan 02 '19 at 17:04

57

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

edited Jan 02 '19 at 17:04

Peter Mortensen

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answered Jun 21 '14 at 11:08

Avinash Raj

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2

Lookahead is completely unnecessary here. – JJJ Jun 21 '14 at 11:13
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This is completely identical to the other answer. – Unihedron Jun 21 '14 at 11:14
he misses the `g` modifier. – Avinash Raj Jun 21 '14 at 11:15
Why do you need `g` modifier? – Toto Jun 21 '14 at 11:31
@M42 `g modifier: global. All matches (don't return on first match)` – Avinash Raj Jun 21 '14 at 11:32
Sure, but it has nothing to do here because we match the whole string. – Toto Jun 21 '14 at 11:33
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without g modifier, it fails to match the string in the second line.http://regex101.com/r/jO2pI2 – Avinash Raj Jun 21 '14 at 11:35
Thanks for the solution guys! :D – Jason Jun 23 '14 at 09:01
Kudos to you for explaining that sh**! :) – gsamaras Dec 12 '15 at 00:29
@AvinashRaj, what should I do to make the first character== last character in your regex. – Menai Ala Eddine - Aladdin May 23 '20 at 23:26

sshashank124 · Answer 2 · 2014-06-21T11:14:52.377

10

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

edited Jun 21 '14 at 11:14

answered Jun 21 '14 at 11:06

sshashank124

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The flag `m` would help as well. – hjpotter92 Jun 21 '14 at 11:07
@hjpotter92, Thank you. I have included it in my answer – sshashank124 Jun 21 '14 at 11:07
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@sshashank124 `.*` would have done instead of `.*?`. Backtracking will be better because of anchor. – Unihedron Jun 21 '14 at 11:12
@Unihedron, Thank you. I have changed my answer. I guess I just feel safer with `.*?` – sshashank124 Jun 21 '14 at 11:15

score 0 · Answer 3 · answered Dec 18 '21 at 10:03

0

 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

answered Dec 18 '21 at 10:03

Naveesh Kumar V

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That is not was asked. – Toto Dec 18 '21 at 10:08

Regular expression to match first and last character

3 Answers3

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