Gurus, How to put Openssl command line into system()?

[john6696]

To all C Gurus,

I want to run this openssl command line inside C.
openssl aes-256-cbc -d -pass pass:"password" -a -salt -in system.aes -out system.txt

Therefore, I type in below source code.

01  #include <stdlib.h> 
02  #include <stdio.h> 
03  #include <string.h> 
04  int main()
05  {
06    char child2[BUFSIZ];
07    strcpy (child2, "openssl aes-256-cbc -d -pass pass:");
08    strcat (child2, ""password" ");
09    strcat (child2, "-a -salt -in system.aes -out system.txt ");
10    printf ("Executing %s\n", child2);
11    system (child2);
12    return 0;
13  }

Then error message came out, debugger point to line 08 because of ""password" " error.
Please guide me how to solve this problem. I am new bird to C world. Thanks...

[anduril462]

When you give us a compiler error, please cut and paste it verbatim, it's easier for everybody.

strcat (child2, ""password" ");

A double quote " is used to mark the beginning and end of a string in C. So when the compiler sees your first quote in that line, it says "this is the start of a string". Then it sees the second quote (red above), and says ok, here's the end of the string, there's nothing in it. Then it sees password. That password is not inside a string, so the compiler thinks it's some sort of identifier, and complains, since strcat has exactly 2 parameters, and is expecting a closing ). You can use single ' around password if you want (your shell shouldn't care), or you can escape the double quote by using \" instead.

EDIT: If you're using an editor with syntax highlighting (which you should), this line would look weird. the word "password" wont have the normal color of a string.

[john6696]

Guru anduril462,

I will try it and get back to you. Thanks.

[john6696]

Guru anduril462,

strcat (child2, "'password' ");

Compile OK.
When executed it appear error message - command not found!
I try to run the openssl command line in prompt $ .... 'password' .... OK.
Did I forgot something ..... ! please guide, thanks.

[anduril462]

It probably means that the location of the openssl command isn't in your $PATH environment variable. Try

strcpy (child2, "/path/to/openssl aes-256-cbc -d -pass pass:")

Of course, replace /path/to with the actual path to your openssl executable.

[john6696]

Guru anduril462,

strcpy (child2, "/usr/bin/openssl aes-256-cbc -d -pass pass:");

compile OK. when run same error! command not found!
Please guide, thanks.

I use Ubuntu 10.04 LTS as my OS plateform (the Lucid Lynx - released in April 2010).

[anduril462]

What is the output of the printf("Executing...") line?

[john6696]

Guru anduril462,

printf("Executing...") exactly like I type manually into the $prompt. It work manually. In C fail!

so sad!

[rags_to_riches]

No, anduril62 wants you to copy and paste the whole output of that line, which according to your original code should print the command line being executed.

[john6696]

Guru rags_to_riches,

Sorry for being late reply to your thread!

#include <stdlib.h> 
#include <stdio.h> 
#include <string.h> 
int main()
{
  char child2[BUFSIZ];
  strcpy (child2, "./usr/bin/openssl aes-256-cbc -d -pass pass:");
  strcat (child2, "'password' ");
  strcat (child2, "-a -salt -in system.aes -out system.txt ");
  printf ("Executing %s\n", child2);
  system (child2);
  return 0;
}

[rags_to_riches]

You're not getting it! What does this line:

printf ("Executing %s\n", child2);

print to the screen when you run the program???

I think you want this:

#include <stdlib.h> 
#include <stdio.h> 
#include <string.h> 
int main()
{
  char child2[BUFSIZ];
  strcpy (child2, "./usr/bin/openssl aes-256-cbc -d -pass pass:");
  strcat (child2, "\"password\" ");
  strcat (child2, "-a -salt -in system.aes -out system.txt ");
  printf ("Executing %s\n", child2);
  system (child2);
  return 0;
}

[john6696]

Guru rags_to_riches,

Thanks! It's worked! By the way, how to give you a rate.

[anduril462]

  strcat (child2, "\"password\" ");

@rags_to_riches: So the only difference is single vs double quotes. I mentioned both methods in my first post, thinking it shouldn't make a difference. Do you know why the shell actually cares about this when invoked via system, but not when it's a login shell? The following simple test on my system seems to suggest the shell doesn't care:

$ cat foo.c
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    printf("Testing single quotes: ls 'filename with spaces'\n");
    system("ls 'filename with spaces'");
    printf("Testing double quotes: ls \"filename with spaces\"\n");
    system("ls \"filename with spaces\"");

    return 0;
}

$ touch "filename with spaces"
$ ls
filename with spaces  foo.c
$ gcc -Wall foo.c
$ ./a.out
Testing single quotes: ls 'filename with spaces'
filename with spaces
Testing double quotes: ls "filename with spaces"
filename with spaces

[john6696]

Guru anduril462,

My fault. When I executed the command, I forgot to put dot in front of backslash. Sorry!

[rags_to_riches]

@anduril462: You're right, it doesn't matter. I rarely if ever use single quotes in the shell, so that was what jumped out at me, rather than the fact the path to openssl was relative to the current directory by use of the leading . rather than the correct path.