Regular expression for adding slashes to string, except first slash in that string

Question

I have string in PHP, like:

"%\u0410222\u0410\u0410%"

And I need to modify the string by adding slashes like:

"%\u0410222\\\\u0410\\\\u0410%"

(add 3 slashes for each slash in string, except first slash) I want to use PHP preg_replace for this case, and how to write regular expression?

probably easier to do the 1->3 for all slashes, then do a 3->1 for the first one. — Marc B
– Marc B, Commented Aug 24, 2015 at 16:18

Casimir et Hippolyte · Accepted Answer · 2015-08-24 17:00:35Z

3

A regex way:

$result = preg_replace('~(?:\G(?!\A)|\A[^\\\]*\\\)[^\\\]*\\\\\K~', '\\\\\\\\\\', $txt);

Note that to figure a literal backslash in a single quoted pattern, you need to use at least 3 backslashes or 4 backslashes for disambiguation (in this case for example \\\\\K). With the nowdoc syntax, only two are needed as you can see in detailed version:

$pattern = <<<'EOD'
~          # pattern delimiter
(?:
    \G     # position after the previous match
    (?!\A) # not at the start of the string
  |           # OR
    \A     # start of the string
    [^\\]* # all that is not a slash
    \\     # a literal slash character
)
[^\\]* \\      
\K             # discard all on the left from the match result
~x
EOD;

Without regex:(maybe more efficient):

$chunks = explode('\\', $txt);
$first = array_shift($chunks);
$result = $first . '\\'. implode('\\\\\\\\', $chunks);

edited Aug 24, 2015 at 17:00

answered Aug 24, 2015 at 16:36

Casimir et Hippolyte

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