/* unix program to copy one file contents to another file*/
/* copyfile.c*/
#include<stdio.h>
#include<unistd.h>
#include<fcntl.h>
#include<stdlib.h>
void main()
{
int fd1,fd2;
int n;
char buf[1024];
fd1=open("takr", O_RDONLY);
/* opening an existing file named takr
in read only mode*/
if(fd1==1)
{
printf("error opening a file");
exit(1);
}
fd2=open("myfile", O_CREAT|O_WRONLY, S_IRWXU);
/*creating a new file named myfile in write only mode with permissions read
write execute to owner*/
/*whenever you are creating a new file
you have to use O_CREAT along with
mode and also specify permissions as a third parameter in open
system call*/
if(fd2==1)
{
printf("\n error opening a file");
exit(1);
}
while((n=read(fd1,buf,5))>0) /* loops until n val bcoms zero, n can have
range 0 to 5 */
/* read system call takes three
parameters first one is file descriptor pointing to first file from where the
data will be read and second one is buffer where the read data will be stored
and third arguments specifies the maximum number of characters that can be
read*/
{
write(fd2,buf,n);
/* same like read
system call but now the data in the buffer will be written to second
file by using file descriptor fd2, third
argument specifies the size of characters to
be written*/
}
}
Output: /home/anil/~
cc copyfile.c
/home/anil/~ ./a.out
/home/anil/~ cat takr
Hi how are you?
/home/anil/~ cat
myfile
Hi how are you?
-------------------------------------------------------------------------------------------------
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