BASH: IF statement doesn't work with empty string from WHILE loop

Question

The first if statement doesn't work if there is no output from the command. I also tried to evaluate the exit status but this also doesn't work?

unhide-tcp output:

# unhide-tcp 
Unhide-tcp 20130526
Copyright © 2013 Yago Jesus & Patrick Gouin
License GPLv3+ : GNU GPL version 3 or later
http://www.unhide-forensics.info
Used options: 
[*]Starting TCP checking

Found Hidden port that not appears in ss: 1025

Found Hidden port that not appears in ss: 1026
[*]Starting UDP checking

Script:

#!/usr/bin/env bash

unhide-tcp | grep "^Found" | while IFS=":" read -a PORT; do

        if [ -z ${PORT[1]} ]; then

            echo "No hidden ports found."

        elif [ -n ${PORT[1]} ]; then

            echo ${PORT[@]}

        fi

done

Answer 1

I think what you simply need is:

unhide-tcp | grep "^Found" || echo "No hidden ports found."

It would print lines like Found Hidden port that not appears in ss: 1025 and if those lines aren't found, script would print "No hidden ports found." instead - because grep returns nonzero if it doesn't find a match.

If you want to condense your output of ports into a single line, you can use sed and readarray with process substitution:

readarray -t PORTS < <(exec unhide-tcp | sed -nr 's|^Found.*: ([0-9]+).*|\1|p')
[[ ${#PORTS[@]} -gt 0 ]] && echo "${PORTS[@]}" || echo "No hidden ports found."

It could give an output like 1025 1026 or No hidden ports found..

Answer 2

Flags such as -z require an argument. In your example the expansion of the $PORT variable may be blank. Wrap the variable name in double quotes.

if [ -z "${PORT[1]}" ]; then ...

Answer 3

You will be better off using awk like this:

unhide-tcp | awk -F':' '/Found/ && NF==2{c++; print} END{if (c==0) print "No hidden ports found"}'

When I used it on the input shown in your question I get this output:

Found Hidden port that not appears in ss: 1025
Found Hidden port that not appears in ss: 1026