i want to match a string that can have any type of whitespace chars (specifically I am using PHP). or any way to tell if a string is empty or just has whitespace will also help!
+6
A:
You don't need regular expressions for that, just use:
if ( Trim ( $str ) === '' ) echo 'empty string';
Jan Hančič
2009-12-02 16:19:39
+1: This will be faster than compiling a regex, and more readable/maintainable.
Ben S
2009-12-02 16:21:10
Thats right, but may not suit for all cases. eg. Dynamically generating pattern and using only once preg_match($pattern, $str)
eyazici
2009-12-02 16:24:07
@Dominic: "Trim" works just as fine as "trim", it's just a matter of coding style :)
Jan Hančič
2009-12-02 16:29:19
And (case-insensitivity aside) beginning a function with an uppercase letter is a style almost all PHP developers would avoid
Ben James
2009-12-02 16:41:08
Like I said, it's a matter of style. I guess I brought that from my .NET days ...
Jan Hančič
2009-12-02 17:57:03
+1
A:
if(preg_match('^[\s]*[\s]*$', $text)) {
echo 'Empty or full of whitespaces';
}
^[\s]* means the text must start with zero or more whitespace end [\s]*$ means must and with zero ro more whitespace, since the expressions are "zero or more", it also matches null strings. It's useess to capture whitespace filled or null strings so I didn't use matching parentheses.
eyazici
2009-12-02 16:20:01
1. there's no matching parentheses in that regex. 2. there's no delimiters either. 3. you might want to explain whether this checks for an empty or a non-empty string.
nickf
2009-12-02 16:27:44
I don't understand all the upvotes for this answer. It is much too verbose. The following regex does exactly the same: `^\s*$`. You don't need to put the `\s` in a character class, and don't need to add it twice. -1 from me, sorry.
Bart Kiers
2009-12-02 18:38:20
When I first write, it was exactly what you say. I have changed it for clarity and nickf's explanation request.
eyazici
2009-12-03 04:24:44
What about `\z`? From the documentation `\Z` matches at end of string, or before newline at the end; where as `\z` matches at end of string only.
PP
2009-12-09 14:18:32
+1
A:
You don't really need a regex
if($str == '') { /* empty string */ }
elseif(trim($str) == '') { /* string of whitespace */ }
else { /* string of non-whitespace */ }
Rob
2009-12-02 16:22:41
+3
A:
if (preg_match('^[\s]*$', $text)) {
//empty
}
else {
//has stuff
}
but you can also do
if ( trim($text) === '' ) {
//empty
}
Edit: updated regex to match a truly empty string - per nickf (thanks!)
Jared
2009-12-02 16:26:00
The first one fails on, ironically, an empty string. Change to a * match and add some delimiters and you're right.
nickf
2009-12-02 16:28:50
+4
A:
Checking the length of the trimmed string, or comparing the trimmed string to an empty string is probably the fastest and easiest to read, but there are some cases where you can't use that (for example, when using a framework for validation which only takes a regex).
Since no one else has actually posted a working regex yet...
if (preg_match('/\S/', $text)) {
// string has non-whitespace
}
or
if (preg_match('/^\s*$/', $text)) {
// string is empty or has only whitespace
}
nickf
2009-12-02 16:32:51