I have simple bash nc script:

nc -k -l 4444 > filename.out

which listens 4444 port for TCP connection. Instead of redirecting received data to filename.out I would like, if possible, to pass each chunk of data (single lines of text) to script.sh as argument. How do I do that?

Thanks in advance.

EDIT: I've also tried with:

nc -k -l 4444 | /path/to/script.sh

but that doesn't work

  • What does "doesn't work" mean? nc -k -l 4444 | perl -nle 'print if m/foo/' prints only input lines containing foo for me.
    – thrig
    Mar 17, 2016 at 21:01
  • @thrig good question. /path/to/script.sh is bash script that should echo $1 > result.txt - fill txt file with $1 argument which it does not. Mar 17, 2016 at 21:07
  • $1 is the first argument to the script, which is not set in your example. nc instead passes the input on standard input, so read it with a while read line; do ...; done loop or cat or something.
    – thrig
    Mar 17, 2016 at 21:14
  • You also might look at inter-process communication using Bash, one example being at stackoverflow.com/questions/10862970/… . And here is another utilizing FIFOs linuxjournal.com/content/using-named-pipes-fifos-bash
    – Thomas N
    Mar 17, 2016 at 21:26

1 Answer 1


This below is the entry point to a multi-input script.

[ $# -ge 1 -a -f "$1" ] && input="$1" || input="-"

# your script's payload here

The #! line is self explanatory I hope

on the second line

$# -ge 1 and is testing for at least one command line argument

-a is the boolean and operator

-f "$1" is testing if the first argument is a file

&& is followed by the directive to be executed if the previous condition holds true

|| is followed by what happens if the test condition is not true

nc -k -l 4444 > filename.out
my_processing_script filename.out


nc -k -l 4444 | my_processing_script

so, if I have an argument and it is a file, my input is this file, if not, my input is coming from the pipe, i.e. "-"

then you can run your thing as you wish. Either

I tested with payload of

awk '{print $2}' ${input}

and my input was coming from netstat -rn command and worked either way. I hope this is what you are asking about

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