Linux Program to Duplicate a File Descriptor with fcntl()

This Linux Program illustrates Duplicating a File Descriptor with fcntl().

Here is the source code of Linux Program to Duplicate a File Descriptor with fcntl(). The Linux Program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

* Linux Program to Duplicate a File Descriptor with fcntl().

```
*/
```
```
 
```
```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
#include <unistd.h>
```
```
#include <sys/types.h>
```
```
#include <sys/stat.h>
```
```
#include <fcntl.h>
```
```
 
```
```
int main(int argc, char **argv)
```
```
{
```
```
    int fd, nfd;
```
```
 
```
```
    if (argc < 2) {
```

        printf("Usage : %s pathname\n", argv[0]);

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        exit(1);
```
```
    }
```
```
 
```

    /* opening the file in write-only mode */

    if ((fd = open(argv[1], O_WRONLY)) < 0) {

        perror("Problem in opening the file");

```
        exit(1);
```
```
    }
```
```
 
```
```
    /* duplicating fd with nfd */
```

    if ((nfd = fcntl(fd, F_DUPFD, 0)) == -1) {

        perror("Problem in duplicating fd");

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        exit(1);
```
```
    }
```

    printf("Fd %d duplicated with %d\n", fd, nfd);

```
 
```
```
    close(fd);
```
```
    close(nfd);
```
```
}
```

 
$ gcc dup_fd.c
$ a.out my_file
 
Fd 3 duplicated with 4

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