Yes. Because Ubuntu's default shell (/bin/sh
) is dash and not bash
. You might use bash
like so -
#include <stdio.h>
int main () {
FILE *fp;
char *cmd = "bash -c 'counter=0;network=$(ls /sys/class/net);"
"num_re=\"^[0-9]+$\";for i in $network;do"
" recv=$(cat /sys/class/net/$i/statistics/rx_bytes) "
"trans=$(cat /sys/class/net/$i/statistics/tx_bytes)"
" r1+=(\"$recv\") t1+=(\"$trans\");" "done; echo $r1 $t1'";
fp = popen (cmd, "r");
while (1) {
int c = fgetc (fp);
if (c == '\0' || feof(fp)) {
break;
}
printf ("%c", c);
}
}
Which outputs
$ sudo ifconfig eth0 up
$ ./a.out
0 0
$ ./a.out
289 762
$ uname -a
Linux eeyore 3.8.0-35-generic #50-Ubuntu SMP Tue Dec 3 01:24:59 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux