CODEWITHSUNDEEP
phpcommand-line-arguments
Derek
Derek

Reputation: 134

PHP exec() with double quote argument

I've been having trouble running a command using PHP's exec() function on Windows. Per a comment on PHP's site on exec():

In Windows, exec() issues an internal call to "cmd /c your_command".

My command looks like:

"path\to\program.exe" -flag1 attribute1 -flag2 attribute2 -flag3 "attribute3 attribute4"

Under regular execution of this command in my local command prompt, without the /c flag, the command runs fine. However, with the introduction of the /c flag, command prompt tells me that "The system cannot find the path specified."

I think the command prompt is interpreting the double-quoted argument as a path to another file, but that's the furthest I've gotten with this problem.

Does anybody have any ideas on how to get past this? Thanks!

Upvotes: 1

Views: 5135

Answers (4)

HappyDog
HappyDog

Reputation: 1341

I also encountered this issue, and the cause of it is, indeed, the internal use of "cmd /c" as described in your own answer.

I have done some investigation, and have found that this was resolved in PHP 5.3, which is why some commenters were unable to reproduce it.

It was fixed in the following commit:

https://github.com/php/php-src/commit/19322fc782af429938da8d3b421c0807cf1b848a#diff-15f2d3ef68f383a87cce668765721041R221

For anyone who still needs to support PHP 5.2, it is fairly easy to replicate the fix in your own code. Instead of:

$cmd = "...any shell command, maybe with multiple quotes...";
exec($cmd);

use

function safe_exec($cmd, &$output = null, &$result_code = null) {
    if (strtoupper(substr(php_uname('s'), 0, 3)) == "WIN"
        && version_compare(PHP_VERSION, "5.3", "<")) 
    {
        $cmd = '"' . $cmd . '"';
    }

    return exec($cmd, $output, $result_code);
}

$cmd = "...any shell command, maybe with multiple quotes...";
safe_exec($cmd);

This replicates the behaviour of PHP 5.3 and above, in the same way as in the above-linked commit.

Note that this applies to all shell commands, not just exec() as used in my example.

Upvotes: 3

Derek
Derek

Reputation: 134

I've figured out the answer by myself...

After perusing cmd.exe's /? and trying to decipher that, I've noticed one important section:

  1. If all of the following conditions are met, then quote characters on the command line are preserved:

    • No /S switch (Strip quotes)
    • Exactly two quote characters
    • No special characters between the two quote characters, where special is one of: & < >( ) @ ^ |
    • There are one or more whitespace characters between the the two quote characters
    • The string between the two quote characters is the name of an executable file.

  2. Otherwise, old behavior is to see if the first character is a quote character and if so, strip the leading character and remove the last quote character on the command line, preserving any text after the last quote character. To negate this behaviour use a double set of quotes "" at the start and end of the command line.

It seems as though if there more than one pair of quotes at any time, quotation marks will be stripped from the second pair of quotes and on.

A relevant question: How do I deal with quote characters when using cmd.exe but not completely relevant, since PHP will not allow you to modify its exec() command by putting an /S flag on its call (which would definitely be a lot easier).

I've managed to work around this problem by directly changing directories with chdir() to the folder where the .exe is located, then chdir()'ing back to my original working directory. It's an extremely hacky solution, given the case that I'm lucky that I only have one set of arguments using double quotes. If anybody were to have multiple arguments using double quotes, I wouldn't know how to solve that...

Upvotes: 2

DEgITx
DEgITx

Reputation: 980

I hope it will help

escapeshellarg() — Escape a string to be used as a shell argument
escapeshellcmd() — Escape shell metacharacters

Upvotes: 0

RobIII
RobIII

Reputation: 8821

Just a guess (I am not familiar with PHP on windows): maybe escape the quotes as " becoming ""?

"path\to\program.exe" -flag1 attribute1 -flag2 attribute2 -flag3 ""attribute3 attribute4""

Whatever the solution is, make sure that when there's some form of user-input that gets passed to this command as arguments that you use escapeshellarg and/or escapeshellcmd.

Upvotes: 0

Related Questions