Regex for lines from /etc/passwd and /etc/group

I've been working on a small Java problem set and have come across some trouble. I'm not very experienced writing regular expressions and could really use two for verifying line entries in /etc/group and /etc/passwd in Java.

I found Regex Verification of Line in /etc/passwd earlier and have yet to test it, but it looks adaptable for what I need. Could anyone else help in providing a regex string for either file?

I'm looking to verify user-entered passwd and group lines, in java,开发者_如何学Python before writing them out to disk. If not, I'll likely end up tokenizing each piece and running various expensive operations.

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Rather than writing a regex you should probably just read the files with Scanner and parse each line with String.split(":"). Then you can check that each part is valid without dealing with a complex expression to handle all cases. It'll probably be easier to write the code and easier to read it later.

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Why do you want to use regular expressions? Just split the line on the colons and inspect the pieces.