[dberebi]

I'm working on CMS that should enable to chose the file name of the published content:
www.domain.com/cms/file-name.php

I want to enable only alphanumeric character underscore and hyphen, so used this regex:
eregi('^[a-z]{1}[\w-]{0,}$',$_POST['fname'])

but this is always false....
why???

[Nico]

PHP Code:

preg_match('~^[\w-]+$~', $_POST['fname']) 

[dberebi]

you can give some explanation please?
I'm newbie to regular expression, what the '~' sign does?

[End User]

Originally Posted by dberebi

you can give some explanation please?
I'm newbie to regular expression, what the '~' sign does?

The tilde (~) is just the expression boundary marker. It can be almost anything, a pipe (|), a slash (/), the pound/octothorpe (#) or whatever you want. It just defines the start and stop of the regex itself.

preg_match('|^[\w-]+$|', $_POST['fname'])

and

preg_match('#^[\w-]+$#', $_POST['fname'])

are the same as

preg_match('~^[\w-]+$~', $_POST['fname'])


Quick RegEx Cheat Sheet

Modifiers
i case-insensitive pattern matching.
g global replace, or replace all
m Treat string as multiple lines. That is, change ``^'' and ``$'' from matching at only the very start or end of the string to the start or end of any line anywhere within the string
s Treat string as single line. That is, change ``.'' to match any character whatsoever, even a newline, which it normally would not match.
x Extend your pattern's legibility by permitting whitespace and comments.


Special Characters
The following should be escaped if you are trying to match that character

\ ^ . $ | ( ) [ ]
* + ? { } ,


Special Character Definitions
\ Quote the next metacharacter
^ Match the beginning of the line
. Match any character (except newline)
$ Match the end of the line (or before newline at the end)
| Alternation
() Grouping
[] Character class
* Match 0 or more times
+ Match 1 or more times
? Match 1 or 0 times
{n} Match exactly n times
{n,} Match at least n times
{n,m} Match at least n but not more than m times


More Special Character Stuff
\t tab (HT, TAB)
\n newline (LF, NL)
\r return (CR)
\f form feed (FF)
\a alarm (bell) (BEL)
\e escape (think troff) (ESC)
\033 octal char (think of a PDP-11)
\x1B hex char
\c[ control char
\l lowercase next char (think vi)
\u uppercase next char (think vi)
\L lowercase till \E (think vi)
\U uppercase till \E (think vi)
\E end case modification (think vi)
\Q quote (disable) pattern metacharacters till \E


Even More Special Characters
\w Match a "word" character (alphanumeric plus "_")
\W Match a non-word character
\s Match a whitespace character
\S Match a non-whitespace character
\d Match a digit character
\D Match a non-digit character
\b Match a word boundary
\B Match a non-(word boundary)
\A Match only at beginning of string
\Z Match only at end of string, or before newline at the end
\z Match only at end of string
\G Match only where previous m//g left off (works only with /g)