Regular Expression, Match Zero or One Parameter from List

Question

String regex = "^-admin -s ([^\\s]+) -port (\\d{4}) -u ([^\\s]+) -konf +([^\\s]+.xml)( -pause)?( -start)?( -stop)?( -save)?( -clean)?( -stat)?( -upload [^ ]+)?( -download [^ ]+)?$";

I need to catch the parameters when my program starts. The initial parameters are required but I have one optional parameter that if provided needs to be one from a specific list.

I use the groups I put the parameters in to check if the optional parameter exists, and if there is only one. If so, I use the name of that parameter to call the associated command. Basically I count the groups that are after the -konf parameter (and xml filename) and if there is more than one parameter I write an error message.

Can I use only regex to make the last parameter optional, and only one from a list? For example, the user should be able to write any one of these parameters:

-pause
-start
-stop
-save
-clean
-stat
-upload datoteka
-download datoteka

Examples:

// pass
-admin -s localhost -port 8000 -u username -konf file.xml -pause
-admin -s localhost -port 8000 -u username -konf file.xml -save
-admin -s localhost -port 8000 -u username -konf file.xml -upload datoteka

These should pass, but the next examples should not because there is more than one command after the -konf parameter.

// fail
-admin -s localhost -port 8000 -u username -konf file.xml -pause -save
-admin -s localhost -port 8000 -u username -konf file.xml -pause -clean

can the parameters be in a different order?: `-pause -user -s localhost -port 8000 -konf file.xml -u username` — Casimir et Hippolyte, Mar 22 '15 at 13:54
just put all the -pause, -save inside a group and make that group as optional. — Avinash Raj, Mar 22 '15 at 13:55
i saw `-admin` in your regex but the example shows `-user` at the start. — Avinash Raj, Mar 22 '15 at 13:56
(Abbreviated) multiple selections, whole group is optional: `( -(pause|start|download [^ ]+))?`. — bloodyKnuckles, Mar 22 '15 at 13:57
no they should be in the order the examples are written @CasimiretHippolyte — InsaneCricket, Mar 22 '15 at 14:02
Seems like tour writing a command line order, this list might help you: http://stackoverflow.com/questions/367706/is-there-a-good-command-line-argument-parser-for-java — Lie Ryan, Mar 22 '15 at 14:04
`(?=\-[\w]+)[\W\w\d\D]*\-konf\W{1}[\W\w\d\D]*\.[\w]+\W([\-\w]+){1}$` is something I've tried and it works with your given inputs (incl. the one that you don't want to pass) — ha9u63a7, Mar 22 '15 at 14:19
@bloodyKnuckles Could you add your answer so I can accept it. — InsaneCricket, Mar 22 '15 at 20:35

bloodyKnuckles · Accepted Answer · 2020-12-31T17:23:36.637

Here is a regular expression that matches zero or one option from a set of options:

( -(pause|start|download [^ ]+))?

Matches either:

-pause
-start
-download filename
// or nothing

But not:

-pause -start
-delete
-download
-download file name with space

Explanation:

Text separated by the pipe symbol | within parenthesis () makes each group between pipes an optional match. For example: (a|b|c) can be read: match letter "a" or "b" or "c". ("ab" and "d" do not match.)

A question mark ? makes what comes before it optional. If the character immediately before is something other than a close paren ) then the question mark makes only that character optional. ab? can be read: match letter "a" by itself, or match an "a" followed by letter "b". ("ac" does not match.)

If the question mark ? is preceded by a close paren ), then the question mark makes everything between the close paren and it's matching open paren ( optional. a(bc)? can be read: match letter a by itself, or match an "a" followed by letter "b" and "c". ("ab" and "ac" and "abd" do not match.)

So we're putting those together: ((a|b|c))? can be read match letter "a" or "b" or "c" or nothing at all.

Regular Expression, Match Zero or One Parameter from List

1 Answers1