Regex of three optional parts with separators

Question

I am trying to parse the three optional components of a string with this format any of these different combinations:

12345,abcd@ABCD   -> $1=12345 $2=abcd $3=ABC
12345,abcd        -> $1=12345 $2=abcd $3=empty
12345@ABCD        -> $1=12345 $2=empty $3=ABC
12345             -> $1=12345 $2=emty $3=empty

Is it possible with a single regexp? I have done several attempts. When the string is complete no problem but the forms with parameters missing are escaping to me:

(.+),(.+)@(.+)           // works when the string is complete
                         //  but how do you express the optionality?
(.+),?(.+)@?(.+)         // nope
(.*)[$,](.*)[$@](.*)     // neither

(Another option, would be splitting the string into the components that looks quite trivial but I am curious about the regexp way)

Answer 1

12345,abcd@ABCD   -> $1=12345 $2=abcd $3=ABC
12345,abcd        -> $1=12345 $2=abcd $3=empty
12345@ABCD        -> $1=12345 $2=empty $3=ABC
12345             -> $1=12345 $2=emty $3=empty

From your expected output it appears that you want empty groups in your matches while matching your inputs. You may use this regex:

/^(\d+),?([^@\n]*)@?(.*)$/g

RegEx Demo

Note that this regex will always return 3 captured groups in every match result.

RegEx Details:

• ^: Start
• (\d+): Match 1+ digits and capture in group #1
• ,?: Match an optional comma
• ([^@]*): Match 0+ any character that is not @ and capture in group #2
• @?: Match an optional @
• (.*): Match 0+ any character and capture in group #3
• $: End

Answer 2

You can use

^([^,@]+)(?:,([^@]+))?(?:@(.+))?$

See the regex demo (note there are newlines added in the demo pattern since the test is performed against a single multiline string there, in real world, the strings to test won't contain newlines, hence they are not in the pattern here.)

Details

• ^ - start of string
• ([^,@]+) - Group 1: one or more chars other than a comma and @
• (?:,([^@]+))? - an optional non-capturing group matching 1 or 0 occurrences of a comma and then (capturing into Group 2) any one or more chars other than @
• (?:@(.+))? - an optional non-capturing group matching 1 or 0 occurrences of a @ char and then (capturing into Group 3) any one or more chars other than line break chars as many as possible
• $ - end of string.