how could I replace the first colon (and this one only) with a comma so I would get the following string?

apache,x:48:48:Apache:/var/www:/sbin/nologin
Also, the code has to support a file with multiple lines and replace the first comma in each line only.
PS C:\> $s = 'apache:x:48:48:Apache:/var/www:/sbin/nologin'
PS C:\> $s -replace '^(.*?):(.*)','$1,$2'
apache,x:48:48:Apache:/var/www:/sbin/nologin
Regexp breakdown:
^(.*?):: shortest match between the beginning of the string and a colon (i.e. the text before the first colon).
(.*): the remainder of the string (i.e. everything after the first colon).
The parantheses group the subexpressions, so they can be referenced in the replacement string as $1 and $2.
Further explanation:
^ matches the beginning of a string.
.* matches any number of characters (. ⇒ any character, * ⇒ zero or more times).
.*? does the same, but gives the shortest match (?) instead of the longest match. This is called a "non-greedy match".
                Thank you for your answer ! :) Would you mind explaining the role of those characters in your regex? Thanks!
– Bluz
                Jul 7 '14 at 13:56
I used the following to solve a count from 1 to 34, but exclude the number 21.
for ($i=101; $i -lt 135; $i++)
    if($i -ne 121)
     {$j = $i -replace '1(.*)','$1'; $j}
        
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