Question

Im running a program in C which calls shell script. The script sometimes shows an error(SIOCSARP: Invalid argument)
The error is not really imporant, it occurs when the program tries to add local IP, it is not important here.

Is there a way to cut any output to the shell in linux here?

Shell script code:

#!/bin/sh
arp -s $1 $2

Running the script:

sprintf(script, "/home/add_arp.sh %s %s", tableI[i].IPaddr, tableI[i].MACaddr);
system(script);

Thanks

Answer 1

If the output you’re seeing is on standard error rather than standard output, you can use:

arp -s $1 $2 2>/dev/null

This will drop all error output in to the bit bucket. If it’s going to standard output and you want to be selective, you can use something like:

arp -s $1 $2 | grep -v 'SIOCSARP: Invalid argument'

This will remove all lines containing that text.

You can also combine standard output and error to the standard output stream and be selective:

arp -s $1 $2 2>&1 | grep -v 'SIOCSARP: Invalid argument'

And finally, if you don’t want to see any output:

arp -s $1 $2 &>/dev/null

Although I wouldn’t use that last one myself unless I was sure I didn’t want to know about any problems.