How to test to see if a string is only whitespace in perl

Whats a good开发者_如何学JAVA way to test to see if a string is only full of whitespace characters with regex?

if($string=~/^\s*$/){
    #is 100% whitespace (remember 100% of the empty string is also whitespace)
    #use /^\s+$/ if you want to exclude the empty string
}

(I have decided to edit my post to include concepts in the below conversation with tobyodavies.)

In most instances, you want to determine whether or not something is whitespace, because whitespace is relatively insignificant and you want to skip over a string consisting of merely whitespace. So, I think what you want to determine is whether or not there are significant characters.

So I tend to use the reverse test: $str =~ /\S/. Determining the predicate "string contains one Significant character".

However, to apply your particular question, this can be determined in the negative by testing: $str !~ /\S/

Your regex statement should look for ^\s+$. It will require at least one whitespace.

In case you were wondering, "white space is defined as [\t\n\f\r\p{Z}]". See http://userguide.icu-project.org/strings/regexp.

\t  Match a HORIZONTAL TABULATION, \u0009.
\n  Match a LINE FEED, \u000A.
\f  Match a FORM FEED, \u000C.
\r  Match a CARRIAGE RETURN, \u000D.
\p{UNICODE PROPERTY NAME}   Match any character with the specified Unicode Property.