alnum character class - Regex - Regular Expression Tutorial

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Regular-expression

Topic

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

Explanation

The [[:alnum:]] character class represents alphabetic and numeric characters, and it is same as using [a-zA-Z0-9] in regular expression.

PHP Example:

    <?php
    $org = 'AAA**&18';
    $det = ereg_replace("[[:alnum:]]","@",$org);
    echo $det;
    ?>

Result:

    @@@**&@@

In the above regex example the character class "[[:alnum:]]" is used along with the metacharacter "^",which specifies to match the begining of the string, since the string has the number "1" in the beginning its matched.

Perl Example:

    #! C:\programfiles\perl\bin\perl
    print "content-type: text/html\n\n";
    $str = "wew436*3631";
    if ( $str =~ /[^[:alnum:]]/ ) 
      {print "Character other than alphanumeric!";} 
    else 
      {print "Only alphanumeric characters!";}

Result:

    Character other than alphanumeric!

In the above example the metacharacter "^" refers the begining of the string, but here its used like "/[^[:alnum:]]/" which means "NOT" a alphanumeric character. Since the string has a "*" it matches as it not a alphanumeric character.

alnum Character Class in Regular expression