PHP-第一个和最后一个字符检查

Question

I am trying a check in PHP. What I want is to check:

• The first character in a string must be a "["
• The last character in a string must be a "]"

I've written this code (last if statement is what I actually want) to check this but am not getting the result I wanted:

$str = "dfgdfg]";

if($str[0] != '[') {
    echo "FIRST NOT EQUAL TO";
}

if(substr($str,-1) != ']') {
    echo "SECOND NOT EQUAL TO";
}


if( ($str[0] != '[') && (substr($str,-1) != ']') ) {
  echo "COND MET!";
}

If I run this code I thought that the last if statement would execute however, only the first if statement executes. What is wrong with the logic in the last if statement?

Answer 1

You have the last statement set as "AND - && " and should be an "OR - ||"

if( ($str[0] != '[') || (substr($str,-1) != ']') ) {
echo "COND MET!";
}

Answer 2

Your final if statement is checking that the first character of your string is NOT a [ , and the last character is also NOT a ] . If you remove the last ] from your $str , you'll see the COND MET output.

if( ($str[0] != '[') && (substr($str,-1) != ']') ) {
  echo "COND MET!";
}

If you want the check to ensure the string both starts and ends with a [ and ] , respectively, you need this:

if( ($str[0] == '[') && (substr($str,-1) == ']') ) {
  echo "COND MET!";
}

Answer 3

简单的RegExr检查如何：

if (preg_match('/^\[.*\]$/', $str) {}