Does dup2(filedescriptor, STDOUT_FILENO) interfere with write and read? - c

Question

I have written this program
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <ctype.h>
#include <sys/stat.h>
#include <fcntl.h>
void redirect(char* filename, char* temp){
chdir("/Users/.....my name..../Desktop");
char buff1[1024];
int fd1, fd2;
if ((fd1 = open(filename, O_RDONLY, S_IRUSR | S_IWUSR | S_IROTH | S_IWOTH)) == -1){
perror("file problem thomas");
exit(1);
}
if ((fd2 = open(temp, O_RDWR | O_CREAT | O_APPEND, S_IRUSR | S_IWUSR | S_IROTH | S_IWOTH)) == -1){
perror("file problem temp");
exit(1);
}
int r = read(fd1, buff1, 1024);
write(fd2, buff1, r);
dup2(fd2, STDOUT_FILENO);
char *args[] = {"ls", NULL};
execvp(args[0], args);
dup2(STDOUT_FILENO, fd2);
close(fd1);
close(fd2);
}
void copy_file(char* filename, char* temp){
chdir("/Users/.....my name ..../Desktop");
int fd1, fd2;
char buffer[1024];
long int n1;
if ((fd1 = open(temp, O_RDONLY))==-1 || ((fd2 = open(filename, O_WRONLY|O_CREAT)) == -1)){
perror("file problem");
exit(1);
}
printf("fd1: %d\n", fd1);
printf("fd2: %d\n", fd2);
while((n1 = read(fd1, buffer, 1024)) > 0){
if (write(fd2, buffer, n1) != n1){
perror("writing problem");
exit(3);
}
}
close(fd1);
close(fd2);
}
int main(){
redirect("thomas", "TEMP");
copy_file("thomas", "TEMP");
}
I have two files "thomas" and "TEMP". What I am trying to do is write the contents of "thomas" into "TEMP", and then write the output of "ls" on the command line to "TEMP", and then write the whole "TEMP" file back into "thomas". For some reason, when I run these two files together, the copy_file function does not run – only redirect will. However, when I run this program without redirect(...), the copy_file function works.
Why is copy_file not running in conjunction with redirect?
Is it something with how I am running dup2(STDOUT_FILENO, fd2) and then not changing the STDOUT file descriptor back?
Any help is appreciated!