Programming

Hello! I know I must take the efforts of learning C..! I need to recompile a binary with the following at the beginning: test if a file exists, remove it and exit. All in "C". As simple as this in sh:

Code:

file=/tmp/filename
if [ -f $file ]; then
    rm -f $file
    exit 0
fi

Thanks!

I think there are a lot of us here who could write that in C in a matter of a few minutes, but you'd not learn anything if any of us did. Thus, I'll offer a few pointers:

Use the man command to determine the calling parameters and how they work. Have fun -- C is a wonderful language.

Hi, agama! Don't forsake me this time! I know I need to learn C, but what you said to me is like speaking in greek! I'm wrestling with a broken binary which is called by initramfs, I tried doing a gpkg-divert on the binary and calling it from a shell script. Something like:

Code:

#!/bin/sh

file=/tmp/filename
if [ -f $file ]; then
    rm -f $file
    exit 0
else
    $0.debian $@ # the name of the diverted binary
fi

Now, the binary is called in the beginning of boot, and it tells: /sbin/binary.debian: not found (while the binary is there...) The script works flawlessly, but fails when called by initramfs.

So I found that I should include this piece of code in the C source, but I don't understand a single piece of code in C and I'm in a big hurry.

I even feel like developing some tools in C (which is IMO the best language - powerful and lightweight), but it's too much for me in such a hurry.

Thanks!

Your request sounded like a homework problem.

Here is a simple programme that unlinks the file named on the command line. You should be able to adapt it to your needs.

Code:

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>


int main( int argc, char **argv )
{
        struct stat buf;

        if( argc <= 1 )
                return;                 // no filename supplied on command line

        if( stat( argv[1], &buf ) >= 0 )        // assume success means the file is there
                unlink( argv[1] );

        return 0;
}

Oh, thanks! I actually got it with:

Code:

FILE *fp = fopen("/tmp/filename","r");
if( fp ) {
    unlink("/tmp/filename");
    exit(EXIT_SUCCESS);
fclose(fp);
}

But unfortunately I thought I would just paste it in the beginning of some int main() and it would work, but is far beyond that... Too many source files and none of them worked. Thanks anyway!

Free the file descriptor back to the system and then unlink it.

Oh, I understand! Thanks! The problem now is that I don't know where to paste this piece of code. I don't know which source file generates the binary... There are too many source files, and none of them is named like the originated binary... From the Makefile is difficult to find it out.