Regex for a-z, 0-9, . and -

Can someone tell me what the syntax for a regex would be that would only allow the following characters:

• a-z (lower case only)
• 0-9
• period, dash, underscore

Additionally the string must start with only a lower case letter (a-z) and cannot contain any spaces or other characters than listed above.

Thank you in advance for the help, Justin

From stackoverflow

• You can do: "^[a-z][-a-z0-9\._]*$"

  Here is the breakdown

  • ^ beginning of line
  • [a-z] character class for lower values, to match the first letter
  • [-a-z0-9\._] character class for the rest of the required value
  • * zero or more for the last class
  • $ end of String
  just somebody : this is wrong. won't match dash, instead you have a range from dot to underscore.

  Justin : When I use this regex with the following string: "test", I get this error: "preg_match() [function.preg-match]: No ending delimiter '^' found" Any idea what this means?

  Laurence Gonsalves : `*` is zero or more repetitions, not one or more.

  notnoop : @Laurence Yes * is zero or more. Thanks

  Laurence Gonsalves : Justin: try putting slashes at the beginning and end of the string. eg: `"/^[a-z][a-z0-9\.\-_]*$/"`

  Roger Pate : What regex flavor requires you to escape `[.]`?

  just somebody : with that backslash it's ok. did i miss it or was the answer edited?

  Justin : That worked with the slashes. Thanks for all the help guys.

  Jonas : The `.` and `-` inside `[]` doesn't need escaping, but it works either way. `[\.\-]` is the same as `[.-]`.

• ^[a-z][a-z0-9._\s-]*
  

  just somebody : this is wrong. won't match dash, which must be either the first or last in the class to be taken literally.

  Dmitry : fixed, thanks for noticing

• [-._a-z0-9]
  

  or

  [-.[:lower:][:digit:]]
  

  or ...

  depends on which version of regular expressions you aim for.

  Justin : I will be using this with preg_match in php.

  just somebody : then it's /^[a-z][-._a-z0-9]*$/