Regular Expression

[Anon]

Hi,

how would I have to build the following expression:

Return "true" if the string starts with exactly one occurance of the substring "Re: ".

Any hints? tia!

[bernicusmaximus]

<?php
$string = "Re: About those cantaloupes!";
$regex = "Re: ";
$result = strncmp($string, $regex, strlen($regex));
if ($result == 0) {
echo ('Found it!');
}
?>

That aught to do ya.

Bernie

[sjokki]

<?php
if (preg_match('/^Re: (?!Re: )/',$str)){
echo 'Exactly one "Re: " at the beginning of $str';
}
?>

I think this is what you wanted.
(?!Re: ) looks ahead to check if there ain't another 'Re: ' after the first one.

You can make the space after 'Re:' optional and the regular case-insensitive with this regex:

<?php
if (preg_match('/^Re: ?(?!Re🙂/i',$str)){
echo 'Exactly one "Re:" at the beginning of $str';
}
?>

[sjokki]

Sorry, my second regex doesn't work good. This one does:
<?php
if (preg_match('/^Re: ?(?! ?Re🙂/i',$str)){
echo 'Exactly one "Re:" at the beginning of $str';
}
?>