Bash script to check iptables rules for loop with if condition

Question

I saved ports in an array that I wanted to check, then I'm running a for loop to check for the port in iptables rule list. I want to echo Ports that are not in the iptables list with msg not found. Tried to add an if condition inside the loop but not working. here's the code: [Non-working ;) ]

#!/bin/bash
array=( 3306 1403 8080 443 22 )
for i in "${array[@]}"
pc=(iptables --list | grep $i | cut -d " " -f1)
do
if [ "${pc}" = "ACCEPT" ]
then 
echo "ok"
else
echo "Port not found"
fi
done

Error:

array.sh: line 4: syntax error near unexpected token `|'
array.sh: line 4: `pc=(iptables --list | grep $i | cut -d " " -f1)'
array.sh: line 5: syntax error near unexpected token `do'
array.sh: line 5: `do'

the pc=... line should certainly be after to "do" keyword. And you probably meant pc=$(...) not pc=(...) — chrslg
– chrslg, Commented Sep 30, 2022 at 18:08
"The whole script doesn't work" could mean many things. Do you get an error? Unexpected output? What output did you expect? — Benjamin W.
– Benjamin W., Commented Sep 30, 2022 at 18:09

sea0003 · Accepted Answer · 2022-09-30 18:10:43Z

1

I am not attempting to syntax check the entire script, but there appears to me an obvious issue; you're assigning the pc evar before the do. This becomes very evident if you format your code with tabs. For example:

#!/bin/bash
array=( 3306 1403 8080 443 22 )

for i in "${array[@]}"
pc=(iptables --list | grep $i | cut -d " " -f1)
do
    if [ "${pc}" = "ACCEPT" ]
    then 
        echo "ok"
    else
        echo "Port not found"
    fi
done

From the above, you can see that pc is not being set inside the for loop. Try this instead:

#!/bin/bash
array=( 3306 1403 8080 443 22 )

for i in "${array[@]}"
do
    pc=$(iptables --list | grep $i | cut -d " " -f1)
    if [ "${pc}" = "ACCEPT" ]
    then 
        echo "ok"
    else
        echo "Port not found"
    fi
done

Edit: Also, @tink (made it 1 minute before me) noticed there's a missing $ in the assignment of the pc variable. I've updated my answer to make that clear as well. HTH

edited Sep 30, 2022 at 18:10

answered Sep 30, 2022 at 18:08

sea0003

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1 Comment

chrslg Over a year ago

Plus pc=$(...) not pc=(...)

tink · Accepted Answer · 2022-09-30 18:05:56Z

0

Two syntax issues:

#!/bin/bash
array=( 3306 1403 8080 443 22 )
for i in "${array[@]}"
do
    pc=$(iptables --list | grep $i | cut -d " " -f1)
    if [ "${pc}" = "ACCEPT" ]
    then 
        echo "ok"
    else
        echo "Port not found"
    fi
done

answered Sep 30, 2022 at 18:05

tink

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Comments

Jetchisel · Accepted Answer · 2022-10-01 11:18:44Z

An alternative using a while + read loop and ProcSub. Instead of embedding grep and cut inside the for loop.

#!/usr/bin/env bash

array=( 3306 1403 8080 443 22 )

regex=$(IFS='|'; printf '%s' "${array[*]}")

while read -r pc port; do
  if [[ "$pc" = "ACCEPT" ]]; then
    printf '%s is Ok.\n' "$port"
  else
    printf >&2 'Port %s not found.\n' "$port"
  fi
done < <(iptables --list | grep -E "$regex")

Tested against a file that contains the following.

ACCEPT 3306
REJECT 1403
REJECT 8080
ACCEPT 443
ACCEPT 22

Change:

iptables --list | grep -E "$regex"

To

cat file.txt | grep -E "$regex"

Just to simulate the iptables command.

Output

3306 is Ok.
Port 1403 not found.
Port 8080 not found.
443 is Ok.
22 is Ok.

That is a minimal assumption from the output of iptables --list, adjust the pattern matching if needed but that is the idea.

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