How can i execute this shellcode " ls PathToDirectory > newFile.txt" in C to create a new file with the list of content of the directory

Question

How can I execute this shellcode ls PathToDirectory > newFile.txt in C to create a new file with the list of content of the directory.

I've tried but this gives me always an error. "ls: cannot access '>': No such file or directory"

I am using this code :

execl( "/bin/ls","ls","PathToTheDirectory" ,">","newFileTocreate.txt" , NULL);

Output:

ls: cannot access '>': No such file or directory newFileTocreate.txt

"Show the content of the directory"

Why do you have to do this in the shell? You can directly read the directory from your C code to get a llist of the files. — Ken White, Nov 10 '19 at 00:17

score 1 · Answer 1 · answered Nov 10 '19 at 00:25

One way would be to use the system call like this example in dols.c

    #include <stdio.h>
    #include <stdlib.h>

    int main(){

        int ret = system("ls > listing.txt");
        if (ret) printf("ERROR: non-zero return %d", ret);

    }

compile and run and check

[C]$ gcc dols.c 
[C]$ ./a.out 
[C]$ more listing.txt 
a.out
dols.c

P.P · Accepted Answer · 2019-11-10T00:38:19.947

Output redirection > is a shell construct that's not understood by execl family functions; they don't invoke a shell to run commands.

What happens is > is passed as an argument to ls which, therefore, says there's no such file in your current directory.

You have few options:

You can use popen(3) to run the command & read the output and then you can write to the file.

char buf[1024] = {0};
FILE *fp = popen("/bin/ls PathToTheDirectory");
while(fgets(buf, sizeof buf, fp)) {
    /* write to newFileToCreate.txt */
}

open(2) the file and duplicate((with dup2) its stdout and then exec it so that output is written to the file.

 int fd = open("newFileToCreate", O_WRONLY | O_CREAT | O_TRUNC);
 dup2(fd, STDOUT_FILENO);
 execl( "/bin/ls", "ls", "PathToTheDirectory", NULL);

Use system(3) which invokes a shell. So you can the command as you have. Although, be aware that this option should be avoided whenever possible. See Issuing system commands in Linux from C, C++
```
system("/bin/ls PathToTheDirectory > newFileTocreate.txt");
```

How can i execute this shellcode " ls PathToDirectory > newFile.txt" in C to create a new file with the list of content of the directory

2 Answers2