How to parse a command line with regular expressions?

Question

I want to split a command line like string in single string parameters. How look the regular expression for it. The problem are that the parameters can be quoted. For exampl

Answer 1

You should not use regular expressions for this. Write a parser instead, or use one provided by your language.

I don't see why I get downvoted for this. This is how it could be done in Python:

>>> import shlex
>>> shlex.split('"param 1" param2 "param 3"')
['param 1', 'param2', 'param 3']
>>> shlex.split('"param 1" param2 "param 3')
Traceback (most recent call last):
    [...]
ValueError: No closing quotation
>>> shlex.split('"param 1" param2 "param 3\\""')
['param 1', 'param2', 'param 3"']

Now tell me that wrecking your brain about how a regex will solve this problem is ever worth the hassle.

Answer 2

("[^"]+"|[^\s"]+)

what i use C++

#include <iostream>
#include <iterator>
#include <string>
#include <regex>

void foo()
{
    std::string strArg = " \"par   1\"  par2 par3 \"par 4\""; 

    std::regex word_regex( "(\"[^\"]+\"|[^\\s\"]+)" );
    auto words_begin = 
        std::sregex_iterator(strArg.begin(), strArg.end(), word_regex);
    auto words_end = std::sregex_iterator();
    for (std::sregex_iterator i = words_begin; i != words_end; ++i)
    {
        std::smatch match = *i;
        std::string match_str = match.str();
        std::cout << match_str << '\n';
    }
}

Output:

"par   1"
par2
par3
"par 4"

Answer 3

Something like:

"(?:(?<=")([^"]+)"\s*)|\s*([^"\s]+)

or a simpler one:

"([^"]+)"|\s*([^"\s]+)

(just for the sake of finding a regexp ;) )

Apply it several time, and the group n°1 will give you the parameter, whether it is surrounded by double quotes or not.

Answer 4

there's a python answer thus we shall have a ruby answer as well :)

require 'shellwords'
Shellwords.shellsplit '"param 1" param2 "param 3"'
#=> ["param 1", "param2", "param 3"] or :
'"param 1" param2 "param 3"'.shellsplit

Answer 5

If you are looking to parse the command and the parameters I use the following (with ^$ matching at line breaks aka multiline):

(?<cmd>^"[^"]*"|\S*) *(?<prm>.*)?

In case you want to use it in your C# code, here it is properly escaped:

try {
    Regex RegexObj = new Regex("(?<cmd>^\\\"[^\\\"]*\\\"|\\S*) *(?<prm>.*)?");

} catch (ArgumentException ex) {
    // Syntax error in the regular expression
}

It will parse the following and know what is the command versus the parameters:

"c:\program files\myapp\app.exe" p1 p2 "p3 with space"
app.exe p1 p2 "p3 with space"
app.exe

Answer 6

Regex: /[\/-]?((\w+)(?:[=:]("[^"]+"|[^\s"]+))?)(?:\s+|$)/g

Sample: /P1="Long value" /P2=3 /P3=short PwithoutSwitch1=any PwithoutSwitch2

Such regex can parses the parameters list that built by rules:

• Parameters are separates by spaces (one or more).
• Parameter can contains switch symbol (/ or -).
• Parameter consists from name and value that divided by symbol = or :.
• Name can be set of alphanumerics and underscores.
• Value can absent.
• If value exists it can be the set of any symbols, but if it has the space then value should be quoted.

This regex has three groups:

• the first group contains whole parameters without switch symbol,
• the second group contains name only,
• the third group contains value (if it exists) only.

For sample above:

1. Whole match: /P1="Long value"
   • Group#1: P1="Long value",
   • Group#2: P1,
   • Group#3: "Long value".
2. Whole match: /P2=3
   • Group#1: P2=3,
   • Group#2: P2,
   • Group#3: 3.
3. Whole match: /P3=short
   • Group#1: P3=short,
   • Group#2: P3,
   • Group#3: short.
4. Whole match: PwithoutSwitch1=any
   • Group#1: PwithoutSwitch1=any,
   • Group#2: PwithoutSwitch1,
   • Group#3: any.
5. Whole match: PwithoutSwitch2
   • Group#1: PwithoutSwitch2,
   • Group#2: PwithoutSwitch2,
   • Group#3: absent.