Php regex how to add a backslash "\"?

Question

I want to add a backslash "\" before all non alphanumeric characters like "how are you \:\)", so I used this:

$code = preg_replace('/([^A-Za-z0-9])/i', '\$1', $code);

But it doesn't work. Instead it just echos '\$1'. What am I doing wrong?

I also tried

$code = preg_replace('/([^A-Za-z0-9])/i', '\\$1', $code);

But won't work.

You missed one \ (as it needs to be escaped, it should be \\$1) — kero
– kero, Commented Aug 20, 2014 at 11:02

mario · Accepted Answer · 2014-08-20 11:05:53Z

4

You need four backslashes:

 $code = preg_replace('/([^A-Za-z0-9])/i', '\\\\$1', $code);

The reason is that the backslash escapes itself in PHP string context (even single quotes). For PCRE to see even one, you need at least two. But to not being misinterpreted to mask the replacement placeholder, you need to double that still. (Btw, three backslashes would also accidentially work.)

answered Aug 20, 2014 at 11:05

mario

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1 Comment

Avinash Raj Over a year ago

echo preg_replace('~([^A-Za-z0-9 ])~', '\\\\$1', $mystring); if you don't want to add \ before spaces.

SagarPPanchal · Accepted Answer · 2014-08-20 11:06:42Z

-1

EXAMPLE:

<?php
$str = "Is your name O'reilly?";

// Outputs: Is your name O\'reilly?
echo addslashes($str);
?>

answered Aug 20, 2014 at 11:06

SagarPPanchal

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