When I add the less than "<" symbol
$str = 'test';
$str = preg_replace('@(.*)@isu', '<$1', $str);
echo $str; // outputs ""
It should output <test, but instead outputs nothing.
It works fine when I don't add the character.
$str = 'test';
$str = preg_replace('@(.*)@isu', '$1', $str);
echo $str; // outputs "test"
I tried escaping it
$str = 'test';
$str = preg_replace('@(.*)@isu', '<\\\\$1', $str);
echo $str; // outputs "<\test"
I was unable to find anything about this in the php manual while google just spits out unrelated SO questions.
I would like to know why this does not work?
PHP 5.4.22
I think you are checking the outputs from the browser. That's why its doing such behaviour. From the console it works perfectly. So, I believe you'll find everything when you view the source of html from browser.
Also, you can replace the < with <
Unclear on how <\\\\$1 would escape the less than (<) symbol? Have you tried this?
$str = 'test';
$str = preg_replace('@(.*)@isu', '\<$1', $str);
echo $str;
EDIT Since it’s been discovered you can view the <test in the source code of a browser, I adjusted my code as follows to make the output human readable in a browser:
$str = 'test';
$str = preg_replace('@(.*)@isu', "<$1", $str);
echo '<pre>';
echo htmlentities($str);
echo '</pre>';
But that outputs:
<test<
As the user anubhava explains, you can add a 1 to the end of the preg_replace to return only the first match:
$str = preg_replace('@(.*)@isu', "<$1", $str, 1);
Which would then output the following which is what the original poster desires:
<test
Use line start and end anchors in your regex:
$str = 'test';
$str = preg_replace('@^(.*)$@isu', '<$1', $str);
echo $str;
OR use .+:
$str = preg_replace('@(.+)@isu', '<$1', $str);
OR with .* specify max replacement count:
$str = preg_replace('@(.*)@isu', '<$1', $str, 1);
OUTPUT:
<test
Problem is by using .* preg_replace is matching and replacing the input string twice, once for the whole input string and once for the end (empty string).