Preserving enters in user's input by PHP

Question

How can you preserve "enters" given by the user in the database and show them then to other users?

I store the question of the user and use the following functions to sanitize the user data, prepare it, and execute the SQL command, respectively.

 pg_escape_string
 pg_prepare
 pg_execute

I use htmlentities with ENT_QUOTES to convert the data HTML. This procedure removes all enters, apparently in the form \n, in the question.

I would like to have a similar question-system as in SO: to show only double enters to users as line breaks.

Answer 1

After you call htmlentities(), call nl2br(). The web browser ignores plain newline characters so you need to convert them to <br /> elements to make them show up.

nl2br — Inserts HTML line breaks before all newlines in a string

Description

string nl2br ( string $string [, bool $is_xhtml= true ] )
Returns string with <br /> or <br> inserted before all newlines.

For example:

echo nl2br(htmlentities($input));

To only show double newlines and ignore single ones, you could instead use a more sophisticated string replacement function, preg_replace:

echo preg_replace('/\n\s*\n/', "<br />\n<br />\n", htmlentities($input));

Here '/\n\s*\n/' matches a newline, followed by any amount of whitespace, followed by another newline. It replaces any such substring with two <br /> elements. Single newlines are ignored. It's also nice because it'll ignore extraneous spaces and tabs that are invisible, such as if a user typed this:

This is a paragraph.\n
It is pretty short.\n
<space><tab>\n
Here's another paragraph.\n
It too is short.

Answer 2

PHP's nl2br() function should do the trick and allow you to convert \n characters to <br> html tags.

To enable the "two enters for a newline" behavior, you should run a regex to turn every pair of consecutive <br> tags into a single <br> tag (you could also do this with \n characters before running nl2br() on the text).