CODEWITHSUNDEEP
clinux
JJang
JJang

Reputation: 25

Input and Output Redirection

So, like how the Linux terminal works.

If I do something like ls -l and type in the command ls -l > hello.txt, it writes whatever was in ls -l to hello.txt.

I'm making a terminal of my own and I'm trying to make it so that when a user types in that same command ls -l > asdf.txt that it writes out ls -l to whatever text file that user inputs.

So here is what I have. My mini-terminal shell works already.

FILE *fp
if (strcmp(args[1], ">") == 0) {
    fp = freopen(args[2], "w+", stdout);
}
fclose(fp);

How would I go to outputting whatever is in the 0th argument into the text file? So like, w > hello.txt would output into hello.txt?

Upvotes: 1

Views: 153

Answers (2)

fluter
fluter

Reputation: 13786

Depends on how you execute the ls command, you can check out popen, it will run the command, and then returns a FILE, which you can read the output of the command from, and then you could write the output into the file for redirection. For example:

FILE *fin = popen("/bin/ls -l", "r");
if (!fp) { ... //handle error }
FILE *fout = freopen(args[2], "w", stdout);
char c;
while ((c = fgetc(fin)) != EOF) {
    fputc(c, fout);
}
pclose(fin);
fclose(fout);

Upvotes: 1

Pooya
Pooya

Reputation: 6126

Assuming you are correct with your arguments (args) you can do the following:

char buffer [1024];
FILE *fp
if (strcmp(args[1], ">") == 0) {
    fp = freopen(args[2], "w+", stdout);
} else {return; }

FILE *cmd;
cmd = popen(args[0],"r");
if(cmd == NULL)
  return;

while (fgets(buffer,sizeof(buffer)-1,cmd)!=NULL)
{
   fprintf(fp,"%s",buffer);
}

fclose(fp);
pclose(cmd);

Upvotes: 1

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