3

I quite this script in bash:

probe='nc -zv localhost 19997'
output=' grep -c 'succeeded' $probe'
if [ $output == '0' ]
then
     echo 'Client online'
else
     echo 'Offline'
fi

The purpose of the script is to check via netcat if a client connected via reverse ssh to my server on port 19997 and print a positive message if this was detectet. nc would print

 Connection to localhost 19997 port [tcp/*] succeeded!

if it detects the client and I would like to grep only the 'succeeded' as a keyword for the established connection and trigger the if-statement via the exit code of grep. But when i run this script I get:

test.sh: line 3: [: too many arguments

Where did I do wrong?

Improve this question
3
  • 2
    You are assigning strings to your variables. You want to use command substitution probe=$(nc...). And quote your expansions: [ "$output" == '0' ]. Commented Dec 27, 2017 at 20:02
  • 2
    You confused a single quote character ' with backqoute `. Commented Dec 27, 2017 at 20:03
  • 1
    Paste your shell scripts in at shellcheck.net to catch these sorts of syntax errors. Commented Dec 27, 2017 at 20:05

1 Answer 1

Reset to default
11

You can test on the results of the command directly like so:

if ( nc -zv localhost 19997 2>&1 >/dev/null ); then
    echo 'Online'
else
    echo 'Offline'
fi

the subshell ( ... ) is not necessary but I like using them when testing like this for cleanliness.

For more reading on exit codes and testing see:

Improve this answer
2
  • I tried to depend the if-statement of the exit-code of grep, but your solution works much better. Many thanks! Commented Dec 27, 2017 at 20:09
  • This is a very elegant solution Commented Dec 28, 2017 at 4:33

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.