Linux bash scripting - Grouping of commands

Question

I'm a newbie in bash scripting and I have a problem with the aggrupation of the commands. Precisely in this line of code:

timeout -s 9 1 echo $var | nc localhost port 

I'm trying to send data of a variable var via netcat to localhost in a specific port, and I want to timeout that command for 1 second. Reading the man pages of timeout I understand that it should be used as:

timeout -s SIGNAL TIME COMMAND 

My question is how to replace COMMAND with the piped command echo $var | nc localhost port and for further knowledge how to write correctly the next situations:

COMMAND1 | (COMMAND2 | COMMAND3) 

and

(COMMAND1 | COMMAND2) | COMMAND3 

If I'm correct, the second example is equivalent to

COMMAND1 | COMMAND2 | COMMAND3 

but I don't know how to write the first one.

Answer 1

That COMMAND is going to be interpreted by timeout, not bash. You cannot put a subshell (the piped commands inside ( and )).

You could put your commands inside a shell script and then pass its name to timeout.

Or actually force COMMAND to be interpreted by bash. This should work:

timeout -s 9 1 bash -c "echo $var | nc localhost port"