CODEWITHSUNDEEP
clinuxshellioio-redirection
Jf2k
Jf2k

Reputation: 119

How to put input/output redirection in your newly-created c shell?

I am wondering if anyone could point me in the right direction on how to do this? For example, if I write "ls > contents.txt", I want the output of ls to be written into content.txt.

This is what I have so far.

 #include <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <ctype.h>

void  parse(char *line, char **argv)
{
     while (*line != '\0') { 
          while (*line == ' ' || *line == '\t' || *line == '\n')
               *line++ = '\0';     
          *argv++ = line;          
          while (*line != '\0' && *line != ' ' && 
                 *line != '\t' && *line != '\n') 
               line++;            
     }
     *argv = '\0';               
}

void  execute(char **argv)
{
     pid_t  pid;
     int    status;

     if ((pid = fork()) < 0) {     
          printf("*** ERROR: forking child process failed\n");
          exit(1);
     }
     else if (pid == 0) {          
          if (execvp(*argv, argv) < 0) {     
               printf("*** ERROR: exec failed\n");
               exit(1);
          }

     }
     else {                                 
          while (wait(&status) != pid)      
               ;
     }
}
void main(char *envp[])
{
    char line[1024];
    char *argv[64];
    while (1){
      printf("shell>>");
      gets(line);
      printf("\n");
      parse(line, argv);
      if (strcmp(argv[0], "exit")==0)
    exit(0);
      execute(argv);
    }
}

Upvotes: 0

Views: 1357

Answers (2)

wojtow
wojtow

Reputation: 975

In between test for pid==0 and before you run execvp(), you want code like this:

int fd=open(outputfile,O_WRONLY|O_CREAT); 
dup2(fd,1);

This will essentially set the stdout for the program run by execvp() to be to this new file. You will have to modify your parsing code to look for the ">" and parse what comes after it as a filename and store in outputfile. You'd also want to do some additional checking to make sure the new file opens OK, etc.

Upvotes: 1

abligh
abligh

Reputation: 25119

You will need to:

  • check for > [filename] in the command passed
  • if that is there, then open the relevant file for output, and use dup2 to attach the fd you get to the stdout of the forked process.

That should be enough to point you in the right direction.

Upvotes: 1

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