linux - Bash empty variable after running cron, but runs manually -

i have simple bash script working manual @ terminal, after cron gives empty variable.

#!/bin/bash  gwip=`/usr/bin/nmcli dev list iface eth0 | grep ip4-settings.gateway: | awk '{ print $2}'` printf '%s\n' "$(date) =- $gwip -= " >> /var/log/looog.log 

run: /bin/bash /test.bash

output in file /var/log/looog.log:

1 monday 2016 14:17:36 +0300 =- 23.18.117.254 -=  

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when run through cron, variable empty.

*/1 * * * * root /bin/bash /test.bash 

output in file /var/log/looog.log:

1 monday 2016 14:19:13 +0300 =-  -= 

why variable $gwip empty? how fix it?

qualifying /usr/bin/nmcli isn't enough -- you're calling bunch of other tools need found path also.

also, in general -- when debugging cron job, arrange stderr go file, so:

#!/bin/bash  # log stdout , stderr 2 different files exec >>/var/log/looog.log 2>>/var/log/looog.err.log  # ...and log every command try execute stderr (aka looog.err.log) set -x  # set path variable export path=/bin:/usr/bin  # original code here, using modern posix $() syntax, vs old hard-to-nest `` gwip=$(nmcli dev list iface eth0 | awk '/ip4-settings[.]gateway:/ { print $2}') printf '%s\n' "$(date) =- $gwip -= " 

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the key things here explicitly-set path (not having value expect set in path common issue in cron jobs), , stderr log (which ensures other issues can identified reading contents).

note use of single redirection looog.log up-front. doesn't make significant difference when you're literally running 1 print statement, if have extended script have more one, it's more efficient open output file 1 re-open every time have write.