CODEWITHSUNDEEP
shellunixportnetstat
max
max

Reputation: 623

How do I determine if a port is in use, e.g. via netstat?

I am trying to check port availability and get a return value using shell script. Example: if port 8080 is free then return true, else return false. Can anyone help? I tried with netstat.

Upvotes: 3

Views: 15428

Answers (3)

Ярослав Рахматуллин
Ярослав Рахматуллин

Reputation: 7931

Assuming you are using netstat from net-tools, this is a working example: 

function is_port_free { 

    netstat -ntpl | grep [0-9]:${1:-8080} -q ; 

    if [ $? -eq 1 ]
    then 
        echo yes 
    else 
        echo no
    fi
}
  • ${1:-8080} means use first argument as port and 8080 if no first argument
  • grep -q [0-9]:port means match a number followed by a colon followed by port
  • $? is the exit value of the previous command. Zero means all went well. Exit values above 0 indicate an error condition. In the context of grep, exit code 1 means no match. The -q means don't do anything but return the exit value.
  • netstat -ltnp means list numeric ports and IPs for all programs that are listening on a tcp port.
  • a | b means process standard output of a with b

eg.

$ is_port_free 8080
yes

$ is_port_free 22
no

Upvotes: 4

ajk
ajk

Reputation: 1055

lsof is your friend:

# lsof -i:8080      # free on my machine
# echo $?
1
# lsof -i:5353      # occupied
COMMAND   PID           USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
mDNSRespo  64 _mdnsresponder    8u  IPv4 0x9853f646e2fecbb7      0t0  UDP *:mdns
mDNSRespo  64 _mdnsresponder    9u  IPv6 0x9853f646e2fec9cf      0t0  UDP *:mdns
# echo $?
0

So in a script, you could use ! to negate the value to test for availability:

if ! lsof -i:8080
then
    echo 8080 is free
else
    echo 8080 is occupied
fi

Upvotes: 18

user590028
user590028

Reputation: 11738

How about something simple:

netstat -an|egrep '[0-9]:8080 .+LISTENING'

Upvotes: 1

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