Question

I’m trying to write a bash script that will log the connection state of a wifi connection by mac address but I’m having some trouble with the syntax of the code.

#!/bin/sh

client="E1:FA:41:23:00:AC"
logfile="/var/logs/wificonn.log"
timestamp=$(date +"%Y%d%m %T")
assoclist=$(wl assoclist | grep $client)
loglast=$(tail -n 1 $logfile | grep $client Not Connected)
notconnmsg="$timestamp $client Not Connected"
connmsg="$timestamp $client Connected"

if [ ! -f $logfile ]; then
    touch $logfile
fi

if [ -z $assoclist  ]; then # Client is not connected
  if [ -n $loglast ]; then # Last log is connected show not connected message
    echo $notconnmsg
    echo $notconnmsg >> $logfile
  fi  
else # Client is connected
  if [ -z $loglast ]; then  # Last log is not connected show connected message
    echo $connmsg
    echo $connmsg >> $logfile
  fi  
fi

This will be run as a cron job every 60seconds and only want it to show/log connected or not connected events only if the opposite is true. I am trying to achieve this by checking the last log entry. eg if last log was not connected and now connected, log to file. This is where the problem is.

thanks

Answer 1

if [ -n $loglast ]; then

Try wrapping $loglast in double quotes:

if [ -n "$loglast" ]; then

When $loglast is empty, bash sees if [ -n ]. You are not evaluating an empty argument, you are evaluating nothing. You can try the following to see the difference:

$ loglast=""
$ if [ -n "$loglast" ]; then echo 'yep'; fi
# <no output>
$ if [ -n $loglast ]; then echo 'yep'; fi
# yep