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copied!<p>If you need to do the exact escape sequences like PHP does, you need the long version, which is the <code>DoubleQuoted</code> class. I extended input string a bit to cover more escape sequences than in your question to make this more generic:</p> <pre><code>$content = '\\\\t\tThis variable\\string is\x20not\40set by me.\nCannot \do anything about it.\n'; $dq = new DoubleQuoted($content); echo $dq; </code></pre> <p>Output:</p> <pre><code>\\t This variable\string is not set by me. Cannot \do anything about it. </code></pre> <p>However, if you're okay to come closely to that, there is a PHP function called <a href="http://php.net/stripcslashes" rel="nofollow noreferrer"><code>stripcslashes</code></a>, for comparison, I've added the result of it and the PHP double-quote string:</p> <pre><code>echo stripcslashes($content), "\n"; $compare = "\\\\t\tThis variable\\string is\x20not\40set by me.\nCannot \do anything about it.\n"; echo $compare, "\n"; </code></pre> <p>Output:</p> <pre><code>\t This variablestring is not set by me. Cannot do anything about it. \\t This variable\string is not set by me. Cannot \do anything about it. </code></pre> <p>As you can see <code>stripcslashes</code> drops some characters here compared to PHP native output.</p> <p>(<strong>Edit:</strong> <a href="https://stackoverflow.com/a/8314506/367456">See my other answer as well</a> which offers something simple and sweet with <code>cstripslashes</code> and <code>preg_replace</code>.)</p> <p>If <code>stripcslashes</code> is not suitable, there is <code>DoubleQuoted</code>. It's constructor takes a string that is treated like a double quoted string (minus variable substitution, only the character escape sequences).</p> <p>As the manual outlines, there are multiple escape sequences. They look like regular expressions, and all start with <code>\</code>, so it's looks near to actually use regular expressions to replace them.</p> <p>However there is one exception: <code>\\</code> will skip the escape sequence. The regular expression would need to have backtracking and/or atomic groups to deal with that and I'm not fluent with those so I just did a simple trick: I only applied the regular expressions to those parts of the string which do not contain <code>\\</code> by simply exploding the string first and then imploding it again.</p> <p>The two regular expression based replace functions, <a href="http://php.net/preg_replace" rel="nofollow noreferrer"><code>preg_replace</code><sup><em>Doc</em></sup></a> and <a href="http://php.net/preg_replace_callback" rel="nofollow noreferrer"><code>preg_replace_callback</code><sup><em>Doc</em></sup></a>, allow to operate on arrays as well, so this is quite easy to do.</p> <p>It's done in the <a href="http://php.net/__toString" rel="nofollow noreferrer"><code>__toString()</code><sup><em>Doc</em></sup></a> function:</p> <pre><code>class DoubleQuoted { ... private $string; public function __construct($string) { $this->string = $string; } ... public function __toString() { $this->exception = NULL; $patterns = $this->getPatterns(); $callback = $this->getCallback(); $parts = explode('\\\\', $this->string); try { $parts = preg_replace_callback($patterns, $callback, $parts); } catch(Exception $e) { $this->exception = $e; return FALSE; # provoke exception } return implode('\\\\', $parts); } ... </code></pre> <p>See the <a href="http://php.net/explode" rel="nofollow noreferrer"><code>explode</code><sup><em>Doc</em></sup></a> and <a href="http://php.net/implode" rel="nofollow noreferrer"><code>implode</code><sup><em>Doc</em></sup></a> calls. Those take care that <code>preg_replace_callback</code> does not operate on any string that contains <code>\\</code>. So the replace operation has been freed from the burden to deal with these special cases. This is the callback function which is invoked by <code>preg_replace_callback</code> for each pattern match. I wrapped it into a closure so it is not publicly accessible:</p> <pre><code>private function getCallback() { $map = $this->map; return function($matches) use ($map) { list($full, $type, $number) = $matches += array('', NULL, NULL); if (NULL === $type) throw new UnexpectedValueException(sprintf('Match was %s', $full)) ; if (NULL === $number) return isset($map[$type]) ? $map[$type] : '\\'.$type ; switch($type) { case 'x': return chr(hexdec($number)); case '': return chr(octdec($number)); default: throw new UnexpectedValueException(sprintf('Match was %s', $full)); } }; } </code></pre> <p>You need some additional information to understand it as this is not the complete class already. I go through the missing points and add the missing code as well:</p> <p>All patterns the class "looks for" contain subgroups, at least one. That one goes into <code>$type</code> and is either the single character to be translated <em>or</em> an empty string for octals and an <code>x</code> for hexadecimal numbers.</p> <p>The optional second group <code>$number</code> is either not set (<code>NULL</code>) or contains the octal/hexadecimal number. The <code>$matches</code> input is normalized to the just named variables in this line:</p> <pre><code>list($full, $type, $number) = $matches += array('', NULL, NULL); </code></pre> <p>Patterns are defined upfront as sequences in a private member variable:</p> <pre><code>private $sequences = array( '(n|r|t|v|f|\\$|")', # single escape characters '()([0-7]{1,3})', # octal '(x)([0-9A-Fa-f]{1,2})', # hex ); </code></pre> <p>The <code>getPatterns()</code> function just wraps those definitions into valid PCRE regular expressions like:</p> <pre><code>/\\(n|r|t|v|f|\$|")/ # single escape characters /\\()([0-7]{1,3})/ # octal /\\(x)([0-9A-Fa-f]{1,2})/ # hex </code></pre> <p>It is pretty simple:</p> <pre><code>private function getPatterns() { foreach($this->sequences as $sequence) $patterns[] = sprintf('/\\\\%s/', $sequence) ; return $patterns; } </code></pre> <p>Now as the patterns are outlined, this explains what <code>$matches</code> contain when the callback function is invoked.</p> <p>The other thing you need to know to understand how the callback works is <code>$map</code>. That's just an array containing the single replacement characters:</p> <pre><code>private $map = array( 'n' => "\n", 'r' => "\r", 't' => "\t", 'v' => "\v", 'f' => "\f", '$' => '$', '"' => '"', ); </code></pre> <p>And that's already pretty much it for the class. There is another private variable <code>$this->exception</code> that is used to store if an exception has been thrown as <code>__toString()</code> can not throw exceptions and would lead to a fatal error if it would happen in the callback function. So it's caught and stored to a private class variable, here again that part of the code:</p> <pre><code> ... public function __toString() { $this->exception = NULL; ... try { $parts = preg_replace_callback($patterns, $callback, $parts); } catch(Exception $e) { $this->exception = $e; return FALSE; # provoke exception } ... </code></pre> <p>In case of an exception while replacing, the function exists with <code>FALSE</code> which will lead to a catchable exception. A getter function makes the internal exception available then:</p> <pre><code>private $exception; ... public function getException() { return $this->exception; } </code></pre> <p>As it's nice to access the original string as well, you can add another getter to obtain that:</p> <pre><code>public function getString() { return $this->string; } </code></pre> <p>And that's the whole class. Hope this is helpful.</p>

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