Question

I am trying to write a shell script that looks if a particular program is running and if it is not, it restarts the service.
Also it checks if the interface is in promiscuous mode. If it is not, it puts it in that mode.

To check if prog xyz is running, I can do the following on commandline

ps -ef | grep -v grep | grep xyz | wc -l

If it returns 0, progrma is not running, else it is running

Similarly to check if the interface is in promisc mode I can do the following on the command line

ip link show eth0 | grep -i promisc | wc -l

Again if return is 1, interface is in promisc mode.

The problem comes when I try to bundle it all in a shell script.

#!/bin/bash
SERVICE="daemonlogger"
x=$(ps -ef|grep -v grep|grep $SERVICE|wc -l)
if [ "$x" -eq 1 ]; then
 run=0
 else
 run=1
fi
IF_NAME="eth0"
y=$(ip link show $IF_NAME|grep -i promisc|wc -l)
if [ "$y" -eq 1 ]; then
 :
 else
 ifconfig $IF_NAME promisc up
fi
if [ "$run" -eq 1 ]; then
 service $SERVICE restart > /dev/NULL 2>&1
fi
echo $run

The output of commands if run from the command line is

[root@dheerajpc Desktop]# ps -ef | grep -v grep | grep daemonlogger | wc -l
0
[root@dheerajpc Desktop]# ip link show eth0 | grep -i promisc | wc -l
0

Here’s the output of running it in debug mode

[root@dheerajpc Desktop]# bash -x check_daemonlogger 
+ SERVICE=daemonlogger
++ ps -ef
++ wc -l
++ grep daemonlogger
++ grep -v grep
+ x=2
+ '[' 2 -eq 1 ']'
+ run=1
+ IF_NAME=eth0
++ grep -i promisc
++ ip link show eth0
++ wc -l
+ y=0
+ '[' 0 -eq 1 ']'
+ ifconfig eth0 promisc up
+ '[' 1 -eq 1 ']'
+ service daemonlogger restart
+ echo 1
1

As can be seen the output of first command is not what is expected, while the output of second command is correct.

What am I doing wrong here?

Answer 1

Hint: What’s your script called?