Writing to both stdout & a file

Question

I have a parent process which forks out a child to perform execv().

I need the output given by execv() to stdout to be displayed onscreen as also copied to a log fil

Answer 1

If you don't want to use a tee, before you write the data, write it to a file, then send it to stdout.

You should write a logging function that does this for you to make it cleaner.

Answer 2

Also, you can use fifo's. mkfifo my.fifo; in execv: program > my.fifo; and open fifo as a regular file, reading from it. This way you can have your stdout parsed, but it has minor drawbacks with shared access.

Answer 3

Do you want only the output of the child to go to the log?

The tee unix command does exactly what you describe: you pipe in data and it writes to a log and to stdout.

Answer 4

Pipe it through tee.

Answer 5

Use Tee like this:

./myprog | tee outputfile

Answer 6

You can use dup2() - this link provides an example