Regular expression to match alphanumeric, hyphen, underscore and space string

Question

I'm trying to match a string that contains alphanumeric, hyphen, underscore and space.

Hyphen, underscore, space and numbers are optional, but the first and last characters must be letters.

For example, these should all match:

abc
abc def
abc123
ab_cd
ab-cd

I tried this:

^[a-zA-Z0-9-_ ]+$

but it matches with space, underscore or hyphen at the start/end, but it should only allow in between.

Answer 1

Use a simple character class wrapped with letter chars:

^[a-zA-Z]([\w -]*[a-zA-Z])?$

This matches input that starts and ends with a letter, including just a single letter.

There is a bug in your regex: You have the hyphen in the middle of your characters, which makes it a character range. ie [9-_] means "every char between 9 and _ inclusive.

If you want a literal dash in a character class, put it first or last or escape it.

Also, prefer the use of \w "word character", which is all letters and numbers and the underscore in preference to [a-zA-Z0-9_] - it's easier to type and read.

Answer 2

Check this working in fiddle http://refiddle.com/refiddles/56a07cec75622d3ff7c10000

This will fix the issue

 ^[a-zA-Z]+[a-zA-Z0-9-_ ]*[a-zA-Z0-9]$