如何在此正则表达式中允许空格？

Question

我是regex的业余爱好者，如何在此regex中允许空格（无所谓）？

if(preg_match('/[^A-Za-z0-9_-]/', $str)) return FALSE;

Answer 1

if(preg_match('/[^A-Za-z0-9_ -]/', $str)) return FALSE;

Note that I put the space before the hyphen. If the space were after the hyphen, I would be specifying a character range from underscore to space. (Issue also evadable by putting a backslash before the hyphen to escape it.)

This is assuming that what you mean by "allow" is: this regex is being used to validate a character string, and if it matches , then the character string is disallowed (hence return FALSE ). So the characters in the negated character class ( [^...] ) are actually the allowed characters. (This is causing some general confusion in this question.)

Answer 2

the in the regular expretion like this '/[^A-Za-z0-9_-\\s]/'
mean the space

Answer 3

Not so much an answer to your question, but a site I find useful for checking regex expressions . It also explains what each part of the expression does / means as you hover over it in the input field.

Answer 4

Your question is unclear. The regular expression, as it stands, will succeed if $str has any character in it that is not A-Za-z0-9_- . Since a space is not one of these characters, the regular expression will match, and the whole statement returns FALSE .

If this isn't what you want, and you want your regular expression to match if $str has any character that is not in A-Za-z0-9_- or a space, then you need to change it to A-Za-z0-9_ - (note the space between the underscore and the hyphen). Thus when your string has a character that is not A-Za-z0-9_ - , the regular expression will match, and your statement will return FALSE . If your string is made up entirely of A-Za-z0-9_ - , then the regular expression will fail to match, and your processing will continue to the next line.

Edit: Here's an example: If your string is abc123def , currently the regular expression will not match and you will not return FALSE . If your string is abc123 def , the regular expression will match and the statement will return FALSE . If you change the character class to A-Za-z0-9_ - , then the regular expression will fail to match for both abc123def and abc123 def , and you will not return FALSE .

Answer 5

If you need to ALLOW only space you'll need '/ /'

If you need to ALLOW any whitespace char (space, tab, newline) - use '/\\s/'

And if you need to add a space to your pattern (means to ignore space) - use /[^A-Za-z0-9_\\ -]/

Answer 6

You only need to add a literal blank space in your negated character class.

It would be more concise to use:

• the case-insensitive flag i and omit one of the letter ranges
• and write [0-9] as \\d

like this:

if (preg_match('/[^A-Z0-9_ -]/i', $str)) return FALSE;

but even better would be to use \\w which represents [A-Za-z0-9_] (which is most of your pattern) to write:

if (preg_match('/[^\w -]/', $str)) return FALSE;

This pattern states that if $str contains any character not in [A-Za-z0-9_ -] then false will be returned.