Only the characters listed on this page need to be escaped in PHP regex matching/replacing.

While < and > can act as delimiter, it doesn't need to be escaped in the given example because you already have /(slash) acting as a delimiter.

Referring to the link in question

The preg_quote() function may be used to escape a string for injection into a pattern and its optional second parameter may be used to specify the delimiter to be escaped.

[\W]+ will match any non-word character.

but to match only the characters from the question, use this:

  $string="sadw$"
  if(preg_match("/[\[^\'£$%^&*()}{@:\'#~?><>,;@\|\\\-=\-_+\-¬\`\]]/", $string)){
   //this string contain atleast one of these [^'£$%^&*()}{@:'#~?><>,;@|\-=-_+-¬`] characters
  }

You don't need to escape curly braces inside the square brackets:

preg_match('!^[a-zA-Z{} ]+$!', $var);

If you need to escape characters, just put a backslash (\) before them. Note: if you're using a double quoted string, you may need to escape the backslashes from interpretation there. For example:

• '\t' matches a tab character;
• "\t" is a tab character; and
• "\\t" is equivalent to '\t'.

In many regex implementations, the following rules apply:

Meta characters inside a character class are:

• ^ (negation)
• - (range)
• ] (end of the class)
• \ (escape char)

So these should all be escaped. There are some corner cases though:

• - needs no escaping if placed at the very start, or end of the class ([abc-] or [-abc]). In quite a few regex implementations, it also needs no escaping when placed directly after a range ([a-c-abc]) or short-hand character class ([\w-abc]). This is what you observed
• ^ needs no escaping when it's not at the start of the class: [^a] means any char except a, and [a^] matches either a or ^, which equals: [\^a]
• ] needs no escaping if it's the only character in the class: []] matches the char ]

You can use preg_quote function:

$pattern = '/line(\s+)' . preg_quote($line, '/') . '/';

You need to double escape \\ because in PHP regex is entered as string where which requires each literal \ as \\ and regex engine needs additional escaping of each \ so you end up with 4 \:

preg_match('/[^\\\\]*$/', 'Foo\Bar\Baz', $output);