PHP表单。 需要检查第一个字母[关闭]

In a form I have an ID field, which needs to check that the first letter is "P" and is 5 characters long.

I have looked into preg_match but I have no idea how to get it working. It seems to be able to check how many "P"s the would be and where they are, but how do I get that to check that only entries starting with "P" are passed.

Big time PHP noobie so doesn't need to be anything awesome. I really don't get PHP. :(

To check if a string starts with P and is 5 characters long, using preg_match, as you asked for, I would write (lazily)

<?php
  if (preg_match('/^P....$/', $your_ID_variable) === 1) {
    print 'your ID is starting with a P and is 5 characters long.';
  }
?>

But as posted from others, there are other ways to do it, like:

<?php
   if ((strlen($your_ID_variable) == 5)
   && (strpos($your_ID_variable, 'P') === 0)) {
    print 'your ID is starting with a P and is 5 characters long.';
   }
?>

Here are some sources you could have found:

• http://www.php.net/manual/en/regexp.reference.meta.php
• http://www.php.net/manual/en/function.preg-match.php
• http://www.php.net/manual/en/function.strlen.php
• http://www.php.net/manual/en/function.strpos.php

You can simply use :

<?php
    $string = 'abcdef';
    $first_character = $string[0];
    if($first_character!="P"){
         //Do something
    }

   //Check length
   if(strlen($string)<6){
       //Do something
   }
?>

Go through : http://php.net/manual/en/function.substr.php for more info.

if (strpos($string, 'P') === 0 && strlen($string) == 5) {
    // do something...
}

You could simplify it into two tasks without regular expressions:

$starts_with_p = (strpos($id_string, 'P') === 0);
$is_five_chars = (strlen($id_string) == 5);

$valid_id = ($starts_with_p && $is_five_chars);

You can simply use this regex to check:

$name = "poiuy";

if(preg_match("%^p.{4}$%i", $name)){
    //do something
}

lets say $id is that variable in which you have id then you can get first character like $id[0] this is faster than substr

and for length you can do strlen($id)

How about this.

$string="Pabcd";
if(preg_match("/^P[A-Za-z]{4}/", $string))
{
echo "string matched";
}
else
{
echo "string not matched";
}

please correct me if iam wrong.