Split string with quotes, reusing method that parses arguments to main

Question

Hi there,

in small program I'm writing, I have to parse a line of user input. Basically what needs to be done is to split the line into an array of strings in the same way as is done with the arguments to main(), ie I'm looking for something like this:

String[] splitArgs(String cmdLine);

I just wonder, if the main methods' arguments are parsed in this way prior to invoking main itself, wouldn't it be possible to call that one instead of writing your own? So, does anyone know where to find that method?

Thanks, Axel

Answer 1

No, that parsing is done by the shell or system library (on Windows), not by Java. You could use ProcessBuilder and sh -c (or cmd on Windows). Something like:

new ProcessBuilder("sh", "-c", "java Program " + cmdLine).start();

Answer 2

On globbing

Command line argument is parsed by the shell; this is why * is usually expanded to a list of files, for example. This is called "globbing", and it happens outside of your program, before the JVM even starts.

See also

• Wikipedia/Glob

Related questions

• Problem of * in Command line argument

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On splitting strings

As for splitting strings into array of strings, your most basic option is String.split(String regex).

Here's a very simple example:

    String[] parts = "one two three".split(" ");
    for (String part : parts) {
        System.out.println("[" + part + "]");
    }

The above prints:

[one]
[two]
[three]

The String argument to split is a regular expression.

References

• regular-expressions.info
• java.lang.regex.Pattern

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Scanner option

Another option you can use is java.util.Scanner. This is a much more improved version of the legacy StringTokenizer.

Related questions

• Split/tokenize/scan a string being aware of quotation marks
  • Example of using Scanner that is aware of simple quotes
• Scanner vs. StringTokenizer vs. String.Split
• Validating input using java.util.Scanner
  • Many examples on validating numbers, vowels, etc

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Guava option

For a more powerful String splitting functionality, you can use e.g. Splitter from Guava.

Answer 3

That sort of parsing is usually done by the shell. So the function you're looking for would be part of a completely separate program, which is probably written in C. By the time the Java VM even gets started, the arguments have already been parsed.