Replace first matching character in string in PowerShell

Question

In the following string,

apache:x:48:48:Apache:/var/www:/sbin/nologin

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.

Ansgar Wiechers · Accepted Answer · 2014-07-07 14:13:29Z

8

Use a regular expression:

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".

answered Jul 7, 2014 at 13:54

Ansgar Wiechers

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2 Comments

Thank you for your answer ! :) Would you mind explaining the role of those characters in your regex? Thanks!

Terrific! Thank you sir! :)