Thread: gzip system() linux - program to unite 2 commands into 1 command

I'm writing a program to turn the two commands "gunzip file.tar.gz" then "tar -xvf file.tar" into "x file.tar.gz", but I've ran into a problem I can't find a solution to, here are the outputs I get depending on if I use a gunzip -f flag in my system() call or not:

if I use: (void)system("gunzip ", store );

> x file.tar.gz
gzip: compressed data not read from a terminal. Use -f to force decompression.
For help, type: gzip -h
store 1: file.tar.gz
tar: option requires an argument -- 'f'
Try `tar --help' or `tar --usage' for more information.
store 2: file.tar

if i use: (void)system("gunzip -f ", store );

> x file.tar.gz
^Cstore 1: file.tar.gz
tar: option requires an argument -- 'f'
Try `tar --help' or `tar --usage' for more information.
store 2: file.tar

(note that ^C is where I had to press ctrl + c as the program just sits there - as far as I know - doing nothing).

Here's my code:

Code:

/* zippy */
#include <stdio.h>
#include <string.h>

int main( int argc, char *argv[] )
{
    if ( argc != 2 ) {
        printf("Usage: unzippy filename.tar.gz\n");
    }
    else {
        /* variables */
        int x, y;    
        char store[40];
        char *ptr = argv[1];

        /* expressions */
        y = strlen( argv[1] );        

        /* store argv[1] for gunzip */
        for (x=0; x<y; x++) {
            store[x] = *ptr;
            ptr = ptr + 1;
            store[x+1] = '\0';
        }

        (void)system( "gunzip ", store );  // or (void)system( "gunzip -f ", store );
        printf("store 1: %s\n", store );     
    //    printf("*ptr: %c\n", *ptr );

        /* reset pointer ready for second for loop */
        ptr = argv[1];
        
        /* store argv[1]-3 for tar -xvf */
        for (x=0; x<y-3; x++) {
            store[x] = *ptr;
            ptr = ptr + 1;
            store[x+1] = '\0';
        }

        (void)system( "tar -xvf ", store );
        printf("store 2: %s\n", store );
    //    printf("*ptr: %c\n", *ptr );
    }
    return 0;
}

I don't know if the problem is something to do with my code or something to do with gunzip and if it is to do with gunzip if I can even solve it with my code? I've tried for a while to find more info and read the gunzip man file, ran "gunzip file.tar.gz" outside of my program and found that it works normally producing file.tar so I suspect the problem is related to system()?

Thanks in advance for any help with the problem itself or for any advice

Well the basic problem seems to be that you haven't read the manual page for system()

It takes a single string.
It does not take a comma separated list of strings and magically transforms them into a usable command line.

Try using say sprintf() to construct a string from all your substrings.

Tar should be able to handle file.tar.gz directly... at least I had no problem running something like

Code:

tar -zxf ../mpc-1.0.1.tar.gz

on linux