I had a situation where I needed to validate an email address that included an apostrophe. It is not widely known that the apostrophe (and a bunch of other symbols for that matter) are valid characters in the official RFC2822 specification for email address formats.

Anyway, I kept getting an error when I tried to add the apostrophe to my character classes in my regex. It gave me a strange error referencing REG_ERANGE. After some googling, I came across this blog post which led me to the answer. The problem is related to the placement of the dash (”-”) character in the regex.

Example 1:

if (ereg("[^a-zA-Z0-9_-.]", $userid)) {
    echo 'bad';
}
else {
    echo 'good';
}

The problem? The dash, or hyphen, being before the period. It thinks it’s a range, like you see in a-z. This may not be a bug, per se, but it’s certainly not smart enough for me.

The solution? Simply put the dash at the end of the regex.

Example 2:

if (ereg("[^a-zA-Z0-9_.-]", $userid)) {
    echo 'bad';
}
else {
    echo 'good';
}

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