alpha character class - Regex - Regular Expression Tutorial

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Regular-expression

Topic

What is [[:alpha:]] Character Class in regex?

Explanation

This character class represents only alphabetic characters that is from [a-zA-Z] in regular expression.

PHP Example:

    <?php
     $str = '1213AAA4232';
     $rslt = ereg_replace("[[:alpha:]]","X",$str);
     echo $rslt;
    ?>

Result:

     1213XXX4232

In the above example for regex the character class "[[:alpha:]]" is used along with "$" to match the string at the end for alphabetical characters alone, since its matched it returns "1".

Perl Example:

    #! C:\programfiles\perl\bin\perl
    print "content-type: text/html\n\n";
    $str = "3333";
    if ( $str =~ /[[:alpha:]]|[[:alnum:]]/) 
      {print "Matches!";} 
    else 
      {print "No Match!";}

Result:

     Matches!

In the above example for regex the string has all numeric characters, in the pattern we use the "OR" or "|" operator with two character classes [[:alpha:]], [[:alnum:]] so that either an alphabhet or a number is matched, so for the above string [[:alnum:]] matches.

alpha Character Class in Regular expression