Question

Simple question but I got a headache to solve this game. Example regex.

[a-zA-Z0-9\s]

[whitespace]Stack[whitespace]Overflow - not allow
Stack[whitespace]Overflow - allow
Stack[whitespace]Overflow[whitespace] - not allow

Let me know

Update regex from JG and it’s working.

function regex($str)
{
    $check = preg_replace('/^[a-zA-Z0-9][a-zA-Z0-9\s]+[a-zA-Z0-9]$|^[a-zA-Z0-9]*$/', "", $str);

    if (empty($check)) {
        return true;
    } else {
        return false;
    }
}

$str = 'Stack Overflow ';
$validator = regex($str);

if ($validator) {
    echo "OK » " .$str;
} else {
    echo "ERROR » " . $str;
}

Answer 1

From what I understood, you want a regex that doesn’t allow your string to have either whitespace at the beginning, or at the end. Something along these lines should work:

/^[a-zA-Z0-9][a-zA-Z0-9\s]+[a-zA-Z0-9]$|^[a-zA-Z0-9]*$/

An example in Python:

import re
test = ["Stack Overflow",
        "Stack&!Overflow",
        " Stack Overflow",
        "Stack Overflow ",
        "x",
        "", 
        " "]
regex = re.compile(r'^[a-zA-Z0-9][a-zA-Z0-9\s]+[a-zA-Z0-9]$|^[a-zA-Z0-9]*$')
for s in test:
    print "'"+s+"'", "=>", "match" if regex.match(s) != None else "non-match"

Output:

'Stack Overflow' => match
'Stack&!Overflow' => non-match
' Stack Overflow' => non-match
'Stack Overflow ' => non-match
'x' => match
'' => match
' ' => non-match