UNIX shell I/O redirection [closed] - c

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I am trying to implement a LINUX shell in C but when I am trying to run a command like this : sort -u < in.txt > out.txt it says : sort: cannot read: '<': No such file or directory . I also tried other commands like ls -l > out.txt etc but it keep telling me the same thing. Here is my code :
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <sys/types.h>
#define LENGTH 1024
int main(){
char line[LENGTH];
char* argv[100];
char* path= "/bin/";
char fullPath[30];
int option;
char* inputFile;
char* outputFile;
while(1){
printf("mysh3>");
if(!fgets(line,LENGTH,stdin)){
break;
}
size_t length = strlen(line);
if(line[length-1]=='\n')
line[length-1] = '\0';
}
char* token;
token = strtok(line," ");
int i = 0;
while(token!=NULL){
argv[i]=token;
token = strtok(NULL," ");
i++;
}
if(argv[1]==">"){
option=1;
outputFile=argv[2];
}
else if(argv[2]==">"){
option = 1;
outputFile=argv[3];
}
else if(argv[1]=="<" && argv[3]==">"){
option=2;
inputFile=argv[2];
outputFile=argv[4];
}
else if(argv[2]=="<" && argv[4]==">"){
option=2;
inputFile=argv[3];
outputFile=argv[5];
}
else if(argv[1]=="<" && argv[3]==">>"){
option=3;
inputFile=argv[2];
outputFile=argv[4];
}
else if(argv[2]=="<" && argv[4]==">>"){
option=3;
inputFile=argv[3];
outputFile=argv[5];
}
argv[i]=NULL;
strcpy(fullPath, path);
strcat(fullPath, argv[0]);
for(int i = 0; i < strlen(fullPath); i++){
if(fullPath[i]=='\n'){
fullPath[i]='\0';
}
}
int ret=forkEx2(argv,inputFile,outputFile,fullPath,option);
if(ret==-1) {
return -1;
}
int forkEx2(char* argv[],char* inputFile,char* outputFile,char
fullPath[],int option){
int fd;
pid_t pid,waitPid;
pid = fork();
if(pid<0){
perror("ERROR: Fork failed.\n");
return -1;
}
else if(pid==0){
if(option==1){
fd=open(outputFile,O_CREAT | O_TRUNC | O_WRONLY, 0600); //if the file does not exist the system create it. Clear all data from the file. Open the file for write only.Store its file descriptor in fd
dup2(fd,STDOUT_FILENO); //replace the standar out with the file
close(fd);
}
else if(option==2){
fd=open(inputFile,O_RDONLY,0600); //open the file for read only
dup2(fd,STDIN_FILENO); //replace the standar in with the file
close(fd);
fd=open(outputFile,O_CREAT | O_TRUNC | O_WRONLY, 0600); //if the file does not exist the system create it. Clear all data from the file. Open the file for write only
dup2(fd,STDOUT_FILENO); //replace the standar out with the file
close(fd);
}
else if(option==3){
fd=open(inputFile,O_RDONLY,0600); //open the file for read only
dup2(fd,STDIN_FILENO); //replace the standar in with the file
close(fd);
fd=open(outputFile, O_APPEND | O_WRONLY, 0600); //append at the end of the file. Open the file for write only
dup2(fd,STDOUT_FILENO); //replace the standar out with the file
close(fd);
}
execvp(fullPath,argv);
perror("ERROR: Child should never arrive here.\n");
}
else{
waitPid = wait(&waitPid);
if (waitPid == -1) {
perror("ERROR: Waitpid failed.\n");
return -1;
}
printf("Parent: Finished pid %d.\n", waitPid);
}
}
}
Any help is appreciated.

Answer 1

let's take that case (it's the same in all cases):
else if(argv[2]=="<" && argv[4]==">"){
option=2;
inputFile=argv[3];
outputFile=argv[5];
}
First, you're comparing strings using ==: that doesn't work. You have to use strcmp or you're comparing the pointers.
Then, you're extracting input file & output file all right, but you forget to remove the redirection arguments from argv. You have to filter them out (by shifting the rest of the argument array each time you encounter one redirection argument)
Aside: you should initialize your argv array or you may meet undefined behaviour if there are not enough arguments.