Ways to build string in c

Question

I'm building a string here based on 4 arguments and calling it with system(), but seems kinda messy the way i have done it. Is there a more correct way i should have done this and not use all those strcat and str1-4?

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

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

    char str1[40] = "sed -n 's/.*\\(";
    char str2[] = "\\)\\(.*\\)\\(";
    char str3[] = "\\).*/\\2/p' ";
    char str4[] = " > ";

    if (argc != 5)
    {
        fprintf (stderr, "Usage %s <LogFile> <token1> <token2> <DumpFile>\n",
                argv[0]);
                exit(EXIT_FAILURE);
    }

    strcat(str1, argv[2]);
    strcat(str1, str2);
    strcat(str1, argv[3]);
    strcat(str1, str3);
    strcat(str1, argv[1]);
    strcat(str1, str4);
    strcat(str1, argv[4]);

    system(str1);

    return 0;
}

Answer 1

One problem with your code is that you're not checking the arguments fit in the 40 bytes.

I would probably use snprintf:

snprintf(str, LENGTH, "sed -n 's/.*\\(%s...", argv[2]...);