快速php正则表达式问题（包括代码）

Question

$first = ".";
$last = "a";
$middle= "testing-123.test";

if (preg_match("[a-zA-Z0-9]", $first)){
 echo 'Frist Returned valid.';
}
if (preg_match("[a-zA-Z0-9.-]", $middle)){
 echo 'Middle Returned valid.';
}
if (preg_match("[a-zA-Z0-9]", $last)){
 echo 'Last Returned valid.';
}

I am breaking down a string into 3 parts using substr so in this example the original text was ".testing-123.testa". I didnt include the substr here but just predefined the variables in this case. I want to check so it means the following requirements:

First character: az, AZ, 0-9 NO SYMBOLS

middle character: az, AZ, 0-9, only . and - symbols

Last character: same as first character.

When I ran above code it echo'd nothing. Any ideas?

Answer 1

You are missing delimitters, try adding / around your regex:

if (preg_match("/[a-zA-Z0-9]/", $first)){
 echo 'Frist Returned valid.';
}
if (preg_match("/[a-zA-Z0-9.-]/", $middle)){
 echo 'Middle Returned valid.';
}
if (preg_match("/[a-zA-Z0-9]/", $last)){
 echo 'Last Returned valid.';
}

You might also want to use preg_match_all to find more/all instances.

Answer 2

if (preg_match("/^[a-z0-9]+$/i", $first)){
 echo 'First Returned valid.';
}
if (preg_match("/^[a-z0-9.-]+$/i", $middle)){
 echo 'Middle Returned valid.';
}
if (preg_match("/^[a-z0-9]+$/i", $last)){
 echo 'Last Returned valid.';
}

should do what you need.

You need delimiters ( / ), and you need to make sure that all characters are tested from the beginning to the end of the string ( ^ and $ anchors).