Question

I am writing a program in C to analyze packets that are captured by tcpdump. In my program I use popen to open a pipe to a tcpdump process which captures the packets and dumps the raw data to stdout as shown below.

FILE *tcpdump = popen("tcpdump -s0 -w -", "r");

However, warnings and error messages from tcpdump go straight to stderr, which is displayed in the console. I would like to somehow hide these, so only the output from my program is shown.

One way i tried was to append 2>&1 to the tcpdump command, but then my program would have to differentiate between tcpdump warnings/errors and the raw packet data.

Is there an easy way to silence the stderr output from tcpdump?

Answer 1

redirect stderr to /dev/null:

FILE *tcpdump = popen("tcpdump -s0 -w - 2>/dev/null", "r");

2>&1 means to redirect stderr to stdout, 2>file means to redirect stderr to file (and redirecting to /dev/null essentially ignores the output)

Look for the redirection explanation in man bash