Bash Script Command Not Executing

Question

I need help with the following Bash v4.1.2 script.

#!/bin/bash

IP=$1
IPTABLES=/sbin/iptables
$IPTABLES -I INPUT -s $IP -j DROP
echo $IPTABLES -I INPUT -s $IP -j DROP |wall

The variables, IP and IPTABLES, get populated in the echo but the line above is not executed. The echo outputs...

/sbin/iptables -I INPUT -s 1.2.3.4 -j DROP

...which is syntactically correct and works if executed manually.

I don't know Bash so I'm struggling to debug this elementary script. I see some scenarios where commands are left bare as I have mine and some that are wrapped in $() (with and without quotes). I've also tried using backticks and quoting various parts of the command. The echo piped through wall only exists for debugging.

I found a basically identical post at Bash script commands not working in cron. My script is not running from cron though.

=== EDIT ===
Added for @Barmar

[root@server tmp]# bash -x /bin/netfilter-drop.sh 
+ IP=1.2.3.4
+ IPTABLES=/sbin/iptables
+ /sbin/iptables -I INPUT -s 1.2.3.4 -j DROP
+ wall
+ echo /sbin/iptables -I INPUT -s 1.2.3.4 -j DROP
[root@server tmp]# 
Broadcast message from root@server (Thu Dec 29 12:46:44 2016):

/sbin/iptables -I INPUT -s 1.2.3.4 -j DROP
^C
[root@server tmp]#

It should work fine. What makes you think it's not executed? — Barmar
– Barmar, Commented Dec 29, 2016 at 18:30
The rule is not added to netfilter. The rule is not displayed by iptables. — user1801810
– user1801810, Commented Dec 29, 2016 at 18:31
The wall makes me think you're not running this from a terminal and therefore can't see all the helpful error messages that the script produces. Add exec &> /tmp/mylog to the start of the script, run it however you do it, then look at the file. If you're invoking it from as web server, @gniourf_gniourf guessed your problem — that other guy
– that other guy, Commented Dec 29, 2016 at 18:45
@thatotherguy and @gniourf_gniourf: Aye! iptables v1.4.7: can't initialize iptables table filter: Permission denied (you must be root) Perhaps iptables or your kernel needs to be upgraded.. So the problem is my sudo. That output was revealed by @thatotherguy's exec suggestion. — user1801810
– user1801810, Commented Dec 29, 2016 at 18:57

user1801810 · Accepted Answer · 2017-01-01 18:02:37Z

0

I had initially only given sudo access to run the posted Bash script. The problem was not the script, rather it was permissions. I needed to give additional sudo access to run iptables in my sudoers. Fixed.

answered Jan 1, 2017 at 18:02

user1801810

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