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Displaying Formatted User Input Page 2

By Ying Zhang
on July 30, 2000

Formatting with Custom Markup Tags

You can provide your own special markup tags for the user to use.
For example, you can allow the to use [b]…[/b] for bolding, and
for italics. Those would be simple string replace operations:

$output = str_replace("[b]", "<b>", $output);
$output = str_replace("[i]", "<i>", $output);

To get a little fancier, we will allow users to add links as well.
For example, the user will be allowed to enter in [link=”url”]…[/link],
which we will turn into a proper <a href=””>…</a> statement.
We can’t use a simple string replace here, instead we need to use regular

$output = ereg_replace('[link="([[:graph:]]+)"]', '<a href="1">', $output);

If you are unfamiliar with the ereg_replace() function, this statement

  • look for all occurrences of [link=”…”] and replace it with <a

[[:graph:]] means any non-whitespace character. See the manual
for more details about regular expressions.

The format_output() function in outputlib.php provides
these markups and a few other ones as well. The general algorithm
would be to:

  1. call htmlspecialchars() on the output text to convert all special
    characters to HTML entities
  2. systematically do string replacements or regexp replacements on our custom
    markup tags


function format_output($output) {


 * Takes a raw string ($output) and formats it for output using a special

 * stripped down markup that is similar to HTML


    $output htmlspecialchars(stripslashes($output));

    /* new paragraph */

$output str_replace('[p]''&lt;p>'$output);

    /* bold */

$output str_replace('[b]''&lt;b>'$output);

$output str_replace('[/b]''&lt;/b>'$output);

    /* italics */

$output str_replace('[i]''&lt;i>'$output);

$output str_replace('[/i]''&lt;/i>'$output);

    /* preformatted */

$output str_replace('[pre]''&lt;pre>'$output);

$output str_replace('[/pre]''&lt;/pre>'$output);

    /* indented blocks (blockquote) */

$output str_replace('[indent]''&lt;blockquote>'$output);

$output str_replace('[/indent]''&lt;/blockquote>'$output);

    /* anchors */

$output ereg_replace('[anchor=&amp;quot;([[:graph:]]+)&amp;quot;]''&lt;a name="1">&lt;/a>'$output);


/* links, note we try to prevent javascript in links */

$output str_replace('[link=&amp;quot;javascript''[link=&amp;quot; javascript'$output);

$output ereg_replace('[link=&amp;quot;([[:graph:]]+)&amp;quot;]''&lt;a href="1">'$output);

$output str_replace('[/link]''&lt;/a>'$output);      





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Ying Zhang