In Regular Expression, the meta-character Brace "[]" is used to match the range of characters like [a-z] or characters like [abc] enclosed within it, but when used with "^" that is like [^abc] the pattern matches character's other than "abc".

Following are some basic brace expressions that can be used for alphabets and numbers.

Not just the above expressions, it can also be used for our convenience like [a-d] for lowercase alphabets from a to d,[0-3] specifies numbers from 0 to 3.If the pattern is specifed like "^[a-Z]" means that the string should start with alphabets either upper or lower case, but if the same pattern is specified like "[^a-z]" matches any number not an alphabet either upper or lower case.

    <?php
    $name = "bit";
    if (preg_match("/b[aeiu]t/", $name))
     {echo "Regex Pattern matches!";} 
    else 
     {echo "Regex Pattern not matched!";}
    ?>

    Pattern matches! 

In the above example "aeiu" is similar to "a|e|i|u", so the possible matches would be "bat","bet","bit", "but".

One can also use advanced patterns like "([A-Z]{2}|[0-9]{5})" matches 2 letters and 5 numbers, so a string can be matched only if it is like "AD78564".

    #! C:\programfiles\perl\bin\perl
    print "content-type: text/html\n\n";
    if ("laa235452er" =~ m/([A-Z]{2}|[0-9]{5})/) 
      {print "The pattern matched.!\n";} 
    else 
      {print "The pattern not found!\n";}

    The pattern matched.! 

In the above example's the pattern "([A-Z]{2}|[0-9]{5})" matches a string if it has "5" numbers and "2" letters.