ip命令无法在crontab的shell脚本中获取IP地址

Question

I use Cloudflare API script to update DDNS on my Raspberry PI using crontab. The shell script works fine in Debian but fails in CentOS/Fedora. While run in the terminal, it works.

I checked out the ip addr could not get data, but I could not solve it. And I tried out that I can instead ip addr with hostname -I, then it works well.

But I am wondering why ip could not work in .sh / bash shell script?

Ferora 28 server Raspberry. I tried many resolvation I can googled, none works.

#!/bin/bash
#this works
ip=$(hostname -I | awk '{print $NF;exit}')
echo $ip>>/usr/local/bin/cloudflare.log 

#this fail
ips=$(ip route get 1:: | awk '{print $(NF-4);exit}')
echo $ips>>/usr/local/bin/cloudflare.log 

# crontab -l
#automatic update ddns per 1 min
* */1 * * *  /usr/local/bin/cf-ddns.sh >/dev/null 2>&1

cat cloudflare.log
xx.xx.xxx.xx
<Blank_None>

Answer 1

crontab dosn't set PATH an cannot find the binarys. Add PATH at the top of your script, or with an export at top of crontab.

# for example
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin