Using preg_replace to modify link to file - php

Question

How to use preg_replace to replace some of a link, but keep the original link as text?
I tried using https://www.phpliveregex.com/#tab-preg-replace, but preg_replace is far to complex for my knowledge.
In short I would like to transform this:
!f:\cases\case\20190813_case.pdf!
To this:
<a href='file://server-files/data/cases/case/20190813_case.pdf'>f:\cases\case\20190813_case.pdf</a>
So that the user sees the network drive as a letter, but the link is actually a link via the server name.
$string = "!f:\cases\case\20190813_case.pdf!"
$string = str_ireplace("F:\\", "file://server-files/Data/", $string);
$string = preg_replace("/\!(.*?)\!/", "<a href='$1'>$1</a>", $string);
This gives:
<a href='file://server-files/Data/cases\case\20190813_case.pdf'>file://server-files/cases/case\20190813_case.pdf</a>
It works fine, but I would like to format link text like this
<a href='file://server-files/Data/cases\case\20190813_case.pdf'>f:\cases\case\20190813_case.pdf</a>
Does anyone know if it is possible?
And it might be possible to skip the str_ireplace, and do it all in the preg_replace line?
EDIT
The actual text is like this (had to a anonymize some parts).
Vi har afleveret et skitseprojekt til et nyt domicil for XXXXX
XXXXXXXX.
Mappen kan ses her !F:\A-sager\XXXXXXXX - nyt
domicil\8-Forslag\D-Sendt\fremlagt for bygherren\20190813 domicil.pdf!
Projektet er endnu ikke offentligt.
The text is urlencoded and stored in a XML file.

Answer 1

There is no reason to use regular expressions for simple string replacements. Not saying you should not get over that bearer and learn them, just not needed here really.
<?php
$str = '!f:\cases\case\20190813_case.pdf!';
$str1 = substr($str, 1, strlen($str) -2);
$str2 = substr($str, 4, strlen($str) -5);
echo "<a href='file://{$str2}'>{$str1}</a>";
//<a href='file://cases\case\20190813_case.pdf'>f:\cases\case\20190813_case.pdf</a>
//if slashes are wrong...
var_dump(str_replace('\\', '/', $str1)) ;//see const DIRECTORY_SEPARATOR
//string(31) "f:/cases/case/20190813_case.pdf"
PHP has a string function for about everything you could ever need.
Update: You stated that there can be multiple links in one "string" (in a question since deleted). You've not provided an example of the format though. Assuming a delimiter of ! and you wanting to use pcre try...
<?php
$str = '!f:\cases\case\20190813_case1.pdf!!f:\cases\case\20190813_case2.pdf!!f:\cases\case\20190813_case3.pdf!';
preg_match_all('#!(.*?)!#', $str, $matches);
var_dump($matches[1]);
There are often many ways to accomplish the same basic string manipulation (strtok, explode, etc).
...Seeing your update, sounds like using some XML parser and iterating over these you should be able to use the examples I've provided, specifically the regular expression to isolate it. Watch for false positives if exclamation marks are in the text? Ask if you get stuck on anything else specific and good luck!
Typically I'd say aim to write the code that is most clear and concise. Readable.

Answer 2

I suggest:
$str = <<<'EOD'
Vi har afleveret et skitseprojekt til et nyt domicil for XXXXX XXXXXXXX.
Mappen kan ses her !F:\A-sager\XXXXXXXX - nyt domicil\8-Forslag\D-Sendt\fremlagt for bygherren\20190813 domicil.pdf!
Projektet er endnu ikke offentligt.
EOD;
echo preg_replace_callback('~!f:(.*?)!~i', function ($m) {
return '<a href="file://server-files/Data'
. strtr(rawurlencode($m[1]), ['%5C'=> '/'])
. '">f:' . $m[1] . '</a>';
}, $str);