redirecting output of execvp into a file in C

Question

I don't know what I am doing wrong... but here is the snippet of code that is being executed:

if (fork() == 0) { // child int fd = open(fileName, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR); dup2(fd, 1); // make stdout go to file execvp("ls","ls"); close(fd); exit(0); } if(wait(&status) == -1) { printf("ERROR REDIRECT\n"); }

fileName gets created but there is nothing inside.What am I doing wrong?

Did you try the exact same code without the dup2? It should print to standard output. This test could help focus on the problem. — ugoren
– ugoren, Commented Jan 30, 2012 at 20:56
@dbeer: That won't work, exec... functions expect executable files, not shell commands. You could use system() though... — dreamlax
– dreamlax, Commented Jan 30, 2012 at 22:14

cnicutar · Accepted Answer · 2012-01-30 20:23:54Z

My guess is that the execvp doesn't work but since you don't handler errors you don't see it.

Try this:

char *const args[] = {"ls", NULL}; execvp(args[0], args); /* If this is reached execvp failed. */ perror("execvp");

Alternatively you can use compound literals:

execvp("ls", (char *[]){"ls", NULL});

Second idea: try to run things normally, without redirect and see how it works.

I tried that and nothing gets printed... it seems that execvp gets executed succesfully.
@user1162954 - There is not a chance in the world your execvp is working. Take cnicutar fix and your stuff will work.

Sandeep Raju · Accepted Answer · 2016-11-15 06:47:40Z

close fd before execvp. because the code after execvp never runs unless execvp fails.

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redirecting output of execvp into a file in C

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