How to get back to stdout after redirection?

Question

I have implemented a shell which supports redirection but after the redirtection is done it gets of of my shell. How can I manage it in a way to get back to shell (stdout)?

 int i;
     for (i=1; args[i];i++)
         {
           if (strcmp(args[i],">")==0)
             {
               printf("argv[i] %s %d \n", args[i], i);
               int out = open(args[i+1], O_WRONLY | O_TRUNC | O_CREAT, S_IRUSR | S_IRGRP | S_IWGRP | S_IWUSR);
               close(1);
               int fdl=dup2(out,1);
               close(out);
               execvp(args[0],args);
            //   open(STDOUT, ">>", \$out); //doesn't work~!
             }

         }

Here's what happens when I execute my shell:

 ./basic_shell 
mysh> pwd > out_pwd
argv[i] > 1 
pwd: ignoring non-option arguments

and it creates out_pwd as expected and writes the pwd result into it. However when I try

mysh>ls > out_ls

I receive this error:

ls cannot access >: No such file or directory

Can you please give me some hints on how to fix it?

score 2 · Answer 1 · answered Sep 27 '13 at 00:22

2

Instead of actually transforming file descriptors in your shell process, you want to simply save a representation of the mapping, and perform the replacements in the child after fork but before you exec the command.

answered Sep 27 '13 at 00:22

R.. GitHub STOP HELPING ICE

208,859
35
376
711

Doing the I/O redirections in the child processes is basically correct. Pipes are slightly different; they have to be created before forking, but the redirection is still done after the fork. – Jonathan Leffler Sep 27 '13 at 04:09

score 0 · Answer 2 · answered Sep 26 '13 at 23:52

0

First close the handle
Then call AllocConsole in kernel32 / or console api in win 7^ to create console

answered Sep 26 '13 at 23:52

Ali Kherad

834
8
25

1

OP is asking about POSIX C code, this answer seems to have something to do with Windows. Whoosh. – Charlie Burns Sep 27 '13 at 00:00
here...http://stackoverflow.com/questions/1908687/how-to-redirect-the-output-back-to-the-screen-after-freopenout-txt-a-stdo – Ali Kherad Sep 27 '13 at 00:17

How to get back to stdout after redirection?

2 Answers2