shell script not working through cron but manually - bash

Question

I'm using below command in a shell script:
echo "1" > log.txt
if [ `ifconfig eth0 | grep 'inet addr' | cut -d ":" -f 2 |
awk {'print $1'}` = 'ipaddress' ] && [ `whoami` = 'userid' ]; then
echo "2" >> log.txt
crontab -l > Cron.txt
echo "3" >> log.txt
fi
The script runs fine when run manually but when scheduled through cron, it
stucks at this IF.
cron entry: 31 11 * * * /home/abc/cron_backup.sh
Output in log.txt Manual run: prints 1,2,3 in log.txt through
cron: prints 1 in log.txt

Answer 1

I would suggest to put as first line of your script the command interpreter line #! to make sure that sh will run it
after that, have you consider to use double bracket syntax [[ ]]?
#!/bin/sh
echo "1" > log.txt
if [[ `ifconfig eth0 | grep 'inet addr' | cut -d ":" -f 2 |
awk {'print $1'}` = 'ipaddress' ]] && [[ `whoami` = 'userid' ]]; then
echo "2" >> log.txt
crontab -l > Cron.txt
echo "3" >> log.txt
fi

Answer 2

The problem could be with the ifconfig, grep, cut awk and whoami calls. When you run it from the command line you have your profile, which has your PATH setting.
When it is run from cron, it does not have your profile. If you modify your PATH variable to point to the location of these programs then you wouldn't have that change when run from cron.
Try putting in the full path for the each of the commands and see it that makes any difference when run from cron.