CODEWITHSUNDEEP
bashnetcat
user2129825
user2129825

Reputation: 81

save result to variable

How can I save result from nc to the variable?

I want:

nc: connect to localhost port 1 (tcp) failed: Connection refused

on my variable. I tried:

a="$(nc -z -v localhost 1)"
echo $a

but output is empty.

Upvotes: 8

Views: 9970

Answers (4)

Johnomated
Johnomated

Reputation: 1

For anyone who might come across this question by searching or from google, wondering why a successful connection saved to a $var returns an empty string, according to this reddit post "All messages from nc itself, as opposed to from the socket, are printed to stderr." So as mentioned by fedorqui and Mickael, you have to redirect stderr to stdout even though it doesn't seem like you're getting an error message.

Example of output to terminal but empty output when calling your $var:

var=$(nc -z -w 10 www.google.com 80) outputs Connection to www.google.com port 80 [tcp/http] succeeded! to the terminal, but when calling echo $var it displays an empty string even though the connection was successful.

Example of saving the stderr output to the $var:

var=$(nc -z -w 10 www.google.com 80 2>&1) runs the nc command, then calling echo $var no longer outputs an empty string, but instead the expected success message Connection to www.google.com port 80 [tcp/http] succeeded!.

Upvotes: 0

Anuj Sethi
Anuj Sethi

Reputation: 21

-w is your friend in this case

-w timeout Connections which cannot be established or are idle timeout after timeout seconds. The -w flag has no effect on the -l option, i.e. nc will listen forever for a connection, with or without the -w flag. The default is no timeout.

nc -z -w 3 $serverName $serverPort

Now you can use the $? variable to use it in your script.

if [ $? == 0 ] can be used to use the output of above command in the scripts. Above command will timeout the connection after 3 seconds if it not able to establish.

Upvotes: 2

fedorqui
fedorqui

Reputation: 290275

Just use $() to get the result of the command:

your_var=$(nc -z -v localhost 1)

If you also want the error to be stored, then redirect the 2 (error) to 1 (normal output):

your_var=$(nc -z -v localhost 1 2>&1)

Upvotes: 14

Mickaël Le Baillif
Mickaël Le Baillif

Reputation: 2156

Just redirect stderr to stdout, expressed by 2>&1:

a="$(nc -z -v localhost 1 2>&1)"
echo $a
nc: connect to localhost port 1 (tcp) failed: Connection refused

File descriptor 2 is attached (unless redirected) to stderr, and fd 1 is attached to stdout. The bash syntax $( ... ) only captures stdout.

Upvotes: 4

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