Thread: Input and output

Hi,

I wrote a shell in C that accepts commands.
Now I need to implement input output redirection.

My shell accepts a string and breaks it down to command and file name if input output redirection is requested.

So for ex:
If the user writes: wc -l < document.txt
My shell will store the command wc-l in a string
and the file name document.txt in another string.
str1[] = "wc - l"
str2[] = "document.txt"

For output redirection it's the same
For ex:
If the user writes ls - l > document.txt
str1[] = "ls - l"
and
str2[] = "document.txt"

Now I want to know how do i tell the shell to do the input output redirection
What instruction should I write before execvp?
if I have str1[] and str2[].

Thanks.
Thanks.

Dunno if it works, but have you tried putting "<" and "document.txt" as arguments in the execvp function? Like:

Code:

args = {"-l", "<", "document.txt"}
execvp("myTest.exe", args)

It's a little unclear as to what you want, here's a shot though.

Code:

   if( freopen(argv[1], "a", stdout) == NULL ) {
        fprintf(stdout,"Error with freopen(): ");
        perror("");
        return 0;
    }

Pretty basic explanation.. freopen takes the filedescripter of stdout, and gives it to argv[1]. Flushing of stdout is performed before doing so.

Couple more system calls (though not standard c) are dup and dup2.