CODEWITHSUNDEEP
windowscommand-linecmd
Artefacto
Artefacto

Reputation: 97845

cmd.exe Command Line Parsing of Environment Variables

I can't figure how to have cmd.exe not interpret something like %PATH% as an environment variable. Given this program:

#include<stdio.h>
#include<windows.h>

int main(int argc, char *argv[])
{
    int i;

    printf("cmd line: %s\n", GetCommandLine());
    for (i = 0; i < argc; i++) {
        printf("%d: %s\n", i, argv[i]);
    }
    return 0;
}

I have these different outputs according to the position of the arguments:

>args "k\" o" "^%PATH^%"
cmd line: args  "k\" o" "%PATH%"
0: args
1: k" o
2: %PATH%

>args "^%PATH^%" "k\" o"
cmd line: args  "^%PATH^%" "k\" o"
0: args
1: ^%PATH^%
2: k" o

I guess it's because cmd.exe doesn't recognize the escaped \" and sees the escaped double quote as closing the first, leaving in the first case %PATH% unquoted. I say this, because if I don't quote the argument, it always works:

>args ^%PATH^% "k\" o"
cmd line: args  %PATH% "k\" o"
0: args
1: %PATH%
2: k" o

but then I can have no spaces...

Upvotes: 0

Views: 1829

Answers (1)

Artefacto
Artefacto

Reputation: 97845

This is apparently possible by also escaping the quotes:

>args ^"oo \\\^" \^" ^%PATH^%^"
cmd line: args  "oo \\\" \" %PATH%"
0: args
1: oo \" " %PATH%

So from what I gather these are the escaping rules:

For the C runtime/CommandLineToArgvW tokenization

  1. Replace \" → \\"
  2. Replace " → \"
  3. Surround the result with double quotes.

For cmd.exe parsing

  • Escape the characters <, >, |, &, ^, ", %, ^ and SPACE by adding the escape character ^.
  • Escaping spaces is unnecessary is the C runtime escape rules were applied and cmd.exe is only to pass the arguments to an another program.

These transformations should be applied in order, first the C runtime rules and then the cmd.exe rules.

If writing something to be interpreted directly by cmd.exe, only the cmd.exe rules should be applied; if starting a program in a way that doesn't involve cmd.exe, only the C runtime rules should be applied.

Here's an example of an argument interpreted directly by cmd.exe, which writes to a file named oo %PATH%:

echo test > oo^ ^%PATH^%

Upvotes: 3

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