php replace group of double backslash - php

Question

how to replace group of double backslash in a string to *
for example:
\\\\a -> **a
\\\a -> *\a
\\a -> *a
\a -> \a
I try use both str_replace and preg_replace but it failed at the second case
str_replace('\\', '*', $str);
preg_replace('/\\\\/', '*', $str);
=> `\\\a` -> `**a`
the reason i want to do this is i want something same as Split string by delimiter, but not if it is escaped but
$str = '1|2\|2|3\\|4\\\|4';
$r = preg_split('~\\\\.(*SKIP)(*FAIL)|\|~s', $str);
var_dump($r);
give me.
0 => string '1' (length=1)
1 => string '2\|2' (length=4)
2 => string '3\|4\\' (length=6)
3 => string '4' (length=1)
i expect something like
[0] => 1
[1] => 2\|2
[2] => 3\\
[3] => 4\\\|4
php 5.4.45-2

Answer 1

A literal backslash in PHP single-quoted strings must be declared with 2 backslashes: to print 1|2\|2|3\\|4\\\|4 you need $str = '1|2\\|2|3\\\\|4\\\\\\|4';.
In a regex, the literal backslash can be matched with 4 backslashes.
Here is an updated PHP code:
$str = '1|2\\|2|3\\\\|4\\\\\\|4';
// echo $str . PHP_EOL; => 1|2\|2|3\\|4\\\|4
$r = preg_split('~\\\\.(*SKIP)(*FAIL)|\\|~s', $str);
var_dump($r);
Result:
array(4) {
[0]=>
string(1) "1"
[1]=>
string(4) "2\|2"
[2]=>
string(3) "3\\"
[3]=>
string(6) "4\\\|4"
}
And to obtain **a from \\a you can thus use
$str = '\\\\a';
$r = preg_replace('~\\\\~s', '*', $str);
See another demo