Tag Archives: bash

Test if a port on a remote system is reachable

With telnet:

telnet webserver.example.com 80

1	telnet webserver.example.com 80

With bash:

cat < /dev/tcp/webserver.example.com/80

1	cat < /dev/tcp/webserver.example.com/80

Replace tcp with udp, depending on what you want.

With netcat:

nc webserver.example.com 80 &> /dev/null; echo $?

1	nc webserver.example.com 80 &> /dev/null; echo $?

If the port is open, you will get an output of 0. If it’s closed, it’s a 1.

..without creating a temporary file:

diff -y <(ls First_directory) <(ls Second_directory)

1	diff -y <(ls First_directory) <(ls Second_directory)

The -y is just to show a side-by-side comparison. Very handy! And the result?

[jorge@j-laptop temp]$ diff -y <(ls First_directory) <(ls Second_directory)
common.txt							common.txt
first_file.txt						      |	second_file.txt

[jorge@j-laptop temp]$ diff -y <(ls First_directory) <(ls Second_directory)

common.txt common.txt

first_file.txt | second_file.txt

Thanks to my colleague Ingvar for showing me this!