Execute C language input file on linux

Two of the three notations are peculiar to Bash; all three are shell notations. The programs that are run need to process the data in quite different ways.

1. (./target <input — input redirection): the target program needs to read standard input to get the information.

   #include <stdio.h>
   
   int main(void)
   {
       int c;
       while ((c = getchar()) != EOF)
           putchar(c);
       return 0;
   }
   

2. (./target <$(cat input) — process substitution): the target program needs to open the file name specified in a command-line argument to get the information.

   #include <stdio.h>
   
   int main(int argc, char **argv)
   {
       if (argc != 2)
       {
           fprintf(stderr, "Usage: %s file\n", argv[0]);
           return 1;
       }
       FILE *fp = fopen(argv[1], "r");
       if (fp == 0)
       {
           fprintf(stderr, "%s: failed to open file '%s' for reading\n",
                   argv[0], argv[1]);
           return 1;
       }
   
       int c;
       while ((c = getc(fp)) != EOF)
           putchar(c);
   
       fclose(fp);
       return 0;
   }
   

3. (./target $(<input) — command substitution): the target program gets the contents of the file split into words as arguments to the program, one word per argument.

   #include <stdio.h>
   
   int main(int argc, char **argv)
   {
       int count = 0;
       for (int i = 0; i < argc; i++)
       {
          count += printf(" %s", argv[i]);
          if (count > 70)
              putchar('\n'), count = 0;
       }
       return 0;
   }
   

The processing needed is quite different, therefore.