Only allowing numbers, letters, dashes, and underscores

[LanceT]

What would the regex be for Only allowing numbers, letters, dashes, and underscores

 

Thanks.

[dsaba]

do some searching, everyone asks this question

 

http://www.phpfreaks.com/tutorials/52/0.php

character classes

if (preg_match('~^[-_a-z0-9]+$~im', '23478sdf935_')) {
echo 'passes';
}

 

 

better yet match what you don't want:

if (!preg_match('~[^-_a-z0-9]+~i', '23478sdf935_')) { //at least 1 char with +, null str ok? use * then
echo 'passes';
}

[LanceT]

What part of the expression allows the underscores and dash?

[dsaba]

Insert Quote

What part of the expression allows the underscores and dash?

 

~^[-_a-z0-9]+$~im

 

[ ] denotes a character class

search google to learn about them

 

a-z, 0-9 are ranges

all other characters are taken as string literals

 

as you can see - and _ are the first two string literals in the char class

 

 

however in this pattern: ~[^-_a-z0-9]+~i

no part of it allows dashes or underscores the ^ symbol matches everything that is not what's in the char class

[effigy]

~^[-_a-z0-9]+$~im

 

Why are you using the /m modifier?

[dsaba]

because the m modifier turns on the meanings for the ^ and $ characters to mean anchors of the start and beginning of a line

[effigy]

From the docs:

 

By default, PCRE treats the subject string as consisting of a single "line" of characters (even if it actually contains several newlines). The "start of line" metacharacter (^) matches only at the start of the string, while the "end of line" metacharacter ($) matches only at the end of the string, or before a terminating newline (unless D modifier is set). This is the same as Perl.  When this modifier is set, the "start of line" and "end of line" constructs match immediately following or immediately before any newline in the subject string, respectively, as well as at the very start and end. This is equivalent to Perl's /m modifier. If there are no "\n" characters in a subject string, or no occurrences of ^ or $ in a pattern, setting this modifier has no effect.

 

In this case, using /m could yield unwanted results for the poster. For example, "a\n-+$%^&#@" would be valid.