RegEx to extract command line arguments - Java

Question

I know there is a lot out there.. But I couldn't figure out how to extract two parameters from Scanner(System.in);

commandline = scanner.readLine();

Two parameters are allowed:

First one can be one of AHG or the digits between 4 to 9. The second parameters again between 4 to 9 OR any number. It should handle all the scenarios:

   "      A    3  " //spaces before and after
   "A    3"         // spaces between the params
   "A    7     6"   // Unwanted 3rd parameter
   "  6  "          // Only one param with spaces.

So how to write Regex for this to extract the above? I tried this one. \\w\\s. But this did not work. I am poor with RegEx.

Frank Puffer · Accepted Answer · 2016-03-27 20:08:49Z

3

Use this on the string returned by readLine():

String [] arguments = commandLine.split( "\\s+" );

The \\s+ stands for at least one whitespace character as separator.

Then check how many elements the array has.

Fimally check the formats of the two arguments

arguments[0].matches("\\s*[AHG4-9]");
arguments[1].matches("\\d");

edited Mar 27, 2016 at 20:08

answered Mar 27, 2016 at 16:35

Frank Puffer

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2 Comments

Kevin Rave Over a year ago

How do I ignore whitespace and extract only the arguments?

Frank Puffer Over a year ago

@KevinRave: That's what commandLine.split( "\\s+" ); should do.

Saleem · Accepted Answer · 2016-03-27 17:14:14Z

2

Try:

public static ArrayList<String> parseArguments(String argument){
    Pattern regex = Pattern.compile("^\\s*([AHG4-9])\\s*(\\d)?\\s*$",
            Pattern.CASE_INSENSITIVE | Pattern.MULTILINE);

    Matcher regexMatcher = regex.matcher(argument);

    if (regexMatcher.find()) {

        ArrayList<String> arguments = new ArrayList<String>();

        arguments.add(regexMatcher.group(1));

        if(regexMatcher.group(2) != null)
        {
            arguments.add(regexMatcher.group(2));
        }

        return arguments;
    }

    return null;

}

Depending on your input:

It will print:

[A,3]

Above regex also enforce argument rules. e.g as you mention first parameter can be A,H,G or number between 4 and 9. 2nd argument any number and can be optional

edited Mar 27, 2016 at 17:14

answered Mar 27, 2016 at 16:38

Saleem

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6 Comments

Frank Puffer Over a year ago

I think you are trying to accomplish too much with a single statement. This makes your code difficult to understand.

Saleem Over a year ago

I'm not sure what do you meant by difficult but tried not only parse arguments but also validate as per OP rules.

Frank Puffer Over a year ago

The regex you are using is probably hard to understand for most programmers who do not use complex regex regularly. Therefore I prefer to split the input first and then validate the arguments in a second step.

Saleem Over a year ago

ah, not understanding regex is a totally different story :P

Kenneth K. Over a year ago

@FrankPuffer How is whitespace; character class; whitespace; optional digit complicated?

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