Re: truncate file with shell

[Tim Wright]

On Tue, 24 Jun 2003, Rex wrote:

> Christopher Sawtell wrote:
> >
> > man 2 truncate
> >
> > System call, You'll have to write a trivial C program to call the kernel
> > function. Surprisingly, nothing in man(1).
>
> Nope, `tis a function.  man 2 truncate.

It is...and I've just written a C program to call it.

You'll need to do something like this to the attachment:

gcc -Wall -o truncate truncate.c

(assuming you save the attachment in a file called "truncate.c" :)

Tim Wright

Assistant Lecturer
Department of Computer Science
University of Canterbury

"Language, like terrorism, targets civilians and generates fear to
effect political change."

  -- "Collateral Language" John Collins and Ross Glover ed.

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

int main( int argc, const char* argv[]) 
{
	off_t length;
	long long temp;

	/* Check number of arguments */
	if (argc!=3) 
	{
		printf("Usage: %s <file> <length>\n", argv[0]);
		return 1;
	}

	/* convert third argument to long long */
	length=atoll(argv[2]);

	/* Check we've got a valid length */
	if (length<1) 
	{
		temp=length;
		printf("Error: can't truncate to %lld length.\n", temp);
		return 1;
	}
	
	/* truncate the file and chekc for errors*/
	if (truncate(argv[1], length)==-1) 
	{
		perror(argv[1]);
		return 1;
	}

	/*hay, we got here OK :) */
	return 0;
}