What is the regular expression for this condition?

i want the regular expression to sanitize my data which should meet the following condition

a) a-z and A-Z allowed

b) 0-9 allowed

c) Special Symbols like Comma (,) dot (.) question Mark (? allowed)

d) Single Space is allowed

i tried and came up with this

preg_replace('%[^a-zA-Z0-9,.?\s]%', '', $string);

i am not so familiar with RegExp, although the above code works, i would like to know

a) if i am using the correct RegExp syntax?

b) if i don't use modulus开发者_JS百科(%) at the start and end of the syntax it won't work, and i have no idea what is the purpose of modulus here?

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If you are requirement is to allow any single whitespace ( which includes space, newline, horizontal tab, vertical tab, form feed etc) then your regex is correct. But if you want to allow only spaces then change the \s to . The call the preg_replace deletes all non-allowed characters from the input.

The % in the call to preg_replace are used as regex delimiters. The preg_ family of functions expect the regex to be within a pair of delimiters. My answer here talks more on what can be used as delimiters.

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a) If it works, it's correct.

b) "When using the PCRE functions, it is required that the pattern is enclosed by delimiters. A delimiter can be any non-alphanumeric, non-backslash, non-whitespace character" - from PHP Documentation

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\s is a whitespace character. Which includes tabs.

Also, if you can allow underscores, \w might make it a bit simpler

\w = [a-zA-Z0-9_]   // \w is a "word" character (including underscores)

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You need to escape dot, comma, and question mark

[^a-zA-Z0-9\,\.\?\s]