regex dont match if it is an empty string

Question

Currently, I am using /^[a-zA-Z.+-. ']+$/ regex to validate incoming strings.

When the incoming string is empty or only contains whitespace, I would like the code to throw an error.

How can I check for empty string using regex? I found some solutions but none are helpful.

Answer 1

You may use

/^(?! *$)[a-zA-Z.+ '-]+$/

Or - to match any whitespace

/^(?!\s*$)[a-zA-Z.+\s'-]+$/

The (?!\s*$) negative lookahead will fail the match if the string is empty or only contains whitespace.

Pattern details

• ^ - start of string
• (?!\s*$) - no empty string or whitespaces only in the string
• [a-zA-Z.+\s'-]+ - 1 or more letters, ., +, whitespace, ' or - chars
• $ - end of string.

Note that actually, you may also use (?!\s+) lookahead here, since your pattern does not match an empty string due to the + quantifier at the end.

Answer 2

Check if the string is empty or not using the following regex:

/^ *$/

The regex above matches the start of the string (^), then any number of spaces (*), then the end of the string ($). If you would instead like to match ANY white space (tabs, etc.), you can use \s* instead of *, making the regex the following:

/^\s*$/