checking exit codes

[ghost]

If I write an exit code in a file to be checked the scritp returns OK either the file contains "0" or "10".
example:

cat /tmp/btrbk_exit_code
10

check_file_content.pl -f /tmp/btrbk_exit_code -i "0"
OK for /tmp/btrbk_exit_code (1 found)

check_file_content.pl -f /tmp/btrbk_exit_code -i "10"
OK for /tmp/btrbk_exit_code (1 found)

But

check_file_content.pl -f /tmp/btrbk_exit_code -i "^0$"
FAILED on /tmp/btrbk_exit_code

which makes things difficult while passing a regexp as a Nagios/Icinga parameter.

Thanks