How can I change iptable entries using bash script? - linux

Question

I have an embedded Linux firmware running on a home router. When I run the following commands one by one from the terminal as root, it works without any errors and serves my purpose. I know this is not a secure policy. This is only to test something.
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
iptables -F
iptables -X
iptables -A INPUT -p tcp -i eth1 --dport 4444 -j ACCEPT
However, when this is run in a bash script as root as below,
#!/bin/bash
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
iptables -F
iptables -X
iptables -A INPUT -p tcp -i eth1 --dport 4444 -j ACCEPT
it gives the following error:
iptables: Bad policy name. Run `dmesg' for more information.
iptables: Bad policy name. Run `dmesg' for more information.
iptables: Bad policy name. Run `dmesg' for more information.
iptables: No chain/target/match by that name.
iptables: No chain/target/match by that name.
I have confirmed that the last line of bash script executes without errors and the entry can be seen in iptables. However, all the other lines throw an error. What am I doing wrong? Surprisingly, the same batch script works fine on my Ubuntu machine.

Answer 1

Did you create the script in Windows, or in some other way that gave it Windows line endings (CRLF) where the router is expecting Unix line endings (LF)?
That would lead to the interpreter reading an extra unprintable character on the end of each of the commands, which would give the errors shown.
You can check by running cat -v myScript.sh. Incorrect Windows line endings will show as:
iptables -P INPUT ACCEPT^M
iptables -P FORWARD ACCEPT^M
iptables -P OUTPUT ACCEPT^M
iptables -F^M
iptables -X^M
iptables -A INPUT -p tcp -i eth1 --dport 4444 -j ACCEPT