2013-02-17 03:13



I'm trying to better understand regular expressions, but can't seem to understand this.

preg_replace("/[^a-zA-Z0-9.?!\s]/", "", $mystring);

I thought that this would not replace dashes, because it would be counted as "through" in the example above. But every time I run it, the dash is removed.

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  • douren7921 douren7921 8年前

    You don't provide a sample $mystring value, which would be helpful.

    As it is written, this regular expression will replace one, and only one, character in $mystring. Specifically, your character class includes a carat character (^) at the very beginning. In any Perl-compatible regular expression engine (of which PHP is one), this indicates not these things (see character classes for more). So your expression is essentially stripping anything that is not:

    • A lowercase letter between a and z
    • An uppercase letter between A and Z
    • A digit between 0 and 9
    • A period
    • A question mark
    • An exclamation mark
    • A whitespace character

    The dash character is not one of the above, so it gets matched and replaced.

    Your assumption about the "through"-ness of the dashes as you have written it are correct, however. The dash character is one of the 4 special characters in a character class, and it gets used to indicate a range of characters.

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