Passing C variable in Shell command

Question

I am stuck at a problem. I want to use C variable in a shell command (dd).

Suppose abc.c is my C program.

int main()
 {
    int block = 1313; /*any integer */
    system("dd if=device of=output-file bs=4096 count=1 skip=$((block))");
    return 0;
 }

Now, if I use 1313 in place of block in the dd command then it works fine. But when I write block then it writes zeros in output-file as block is a C program variable and is used in the shell command.

You haven't googled this one, have you. And you don't know the difference between PHP and C, do you. — user529758
– user529758, Commented Jun 28, 2013 at 10:26

unwind · Accepted Answer · 2013-06-28 10:56:05Z

6

Use snprintf().

char buf[256];
const int block = 1313;
snprintf(buf, sizeof buf,
         "dd if=device of=output-file bs=4096 count=1 skip=%d", block);
system(buf);

edited Jun 28, 2013 at 10:56

unwind

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answered Jun 28, 2013 at 10:26

mattn

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