In PHP do i need to escape backslashes?

Question

I think this may be a stupid question, but I am quite confused whether I need to escape backslash in PHP.

echo \'Application\\Models\\User\'; prints Applicat         


        

Answer 1

In single quoted strings only the escape sequences \\ and \' are recognized; any other occurrence of \ is interpreted as a plain character.

So since \M and \U are no valid escape sequences, they are interpreted as they are.

Answer 2

I think it depends on the context, but it is a good idea to escape backslashes if using it in file paths.

Another good idea is to assign the directory separator to a constant, which I've seen done in various applications before, and use it as thus:

<?php
define('DIRECTORY_SEPARATOR', '\\');

echo 'Application'.DIRECTORY_SEPARATOR . 'Models' . DIRECTORY_SEPARATOR . 'User';
?>

If you wish to save space and typing, others use DS for the constant name.

<?php
define('DS', '\\');

echo 'Application'.DS.'Models'.DS.'User';
?>

This keeps your application portable if you move from a Windows environment to a *nix environment, as you can simple change the directory separator constant to a forward slash.

Answer 3

In single quoted strings, it's optional to escape the backslash, the only exception is when it's before a single quote or a backslash (because \' and \\ are escape sequences).

This is common when writing regular expressions, because they tend to contain backslashes. It's easier to read preg_replace('/\w\b/', ' ', $str) than /\\w\\b/.

See the manual.

Answer 4

You will find the complete explanation here: http://nl.php.net/manual/en/language.types.string.php

Answer 5

Since your last example contains a quote ('), you need to escape such strings with addslashes function or simply adding a slash yourself before it like this:

'Application\Model\\'User'

Answer 6

If it is to be used in an HTML page, then you might as well use code \ to represent a backslash, like so:

echo 'Application\Models\User';

It will print:

Application\Models\User