AWK to get details from /proc/net/tcp and /proc/net/udp when netstat and lsof are not available

awk_netstat.sh

# Gawk version
# Remote
grep -v "rem_address" /proc/net/tcp  | awk  '{x=strtonum("0x"substr($3,index($3,":")-2,2)); for (i=5; i>0; i-=2) x = x"."strtonum("0x"substr($3,i,2))}{print x":"strtonum("0x"substr($3,index($3,":")+1,4))}'

# Local
grep -v "rem_address" /proc/net/tcp | awk  '{x=strtonum("0x"substr($2,index($2,":")-2,2)); for (i=5; i>0; i-=2) x = x"."strtonum("0x"substr($2,i,2))}{print x":"strtonum("0x"substr($2,index($2,":")+1,4))}'

# No Gawk
# Local
grep -v "rem_address" /proc/net/tcp  | awk 'function hextodec(str,ret,n,i,k,c){
    ret = 0
    n = length(str)
    for (i = 1; i <= n; i++) {
        c = tolower(substr(str, i, 1))
        k = index("123456789abcdef", c)
        ret = ret * 16 + k
    }
    return ret
} {x=hextodec(substr($2,index($2,":")-2,2)); for (i=5; i>0; i-=2) x = x"."hextodec(substr($2,i,2))}{print x":"hextodec(substr($2,index($2,":")+1,4))}'

# Remote
grep -v "rem_address" /proc/net/tcp | awk 'function hextodec(str,ret,n,i,k,c){
    ret = 0
    n = length(str)
    for (i = 1; i <= n; i++) {
        c = tolower(substr(str, i, 1))
        k = index("123456789abcdef", c)
        ret = ret * 16 + k
    }
    return ret
} {x=hextodec(substr($3,index($3,":")-2,2)); for (i=5; i>0; i-=2) x = x"."hextodec(substr($3,i,2))}{print x":"hextodec(substr($3,index($3,":")+1,4))}'


# All in one
awk 'function hextodec(str,ret,n,i,k,c){
    ret = 0
    n = length(str)
    for (i = 1; i <= n; i++) {
        c = tolower(substr(str, i, 1))
        k = index("123456789abcdef", c)
        ret = ret * 16 + k
    }
    return ret
}
function getIP(str,ret){
    ret=hextodec(substr(str,index(str,":")-2,2)); 
    for (i=5; i>0; i-=2) {
        ret = ret"."hextodec(substr(str,i,2))
    }
    ret = ret":"hextodec(substr(str,index(str,":")+1,4))
    return ret
} 
NR > 1 {{if(NR==2)print "Local - Remote";local=getIP($2);remote=getIP($3)}{print local" - "remote}}' /proc/net/tcp

awesome 👏

Thank you!

I know readability is important, but here is a shorter version working on POSIX shell, tested with gawk, nawk and Busybox awk (didn't note the version of each, sorry):

awk $(case "$(awk --version 2>&-)" in GNU*) echo --non-decimal-data;;esac) \
 'function g(s){r=sprintf("%d","0x" substr(s,index(s,":")-2,2));for (i=5;i>0;i-=2){r=r"."sprintf("%d","0x" substr(s,i,2))};return r":"sprintf("%d", "0x" substr(s,index(s,":")+1,4))}NR>1{print g($2),g($3)}'\
 /proc/net/tcp # or /proc/$PID/net/tcp for a process ports

Append a | column -t to make it more readable.

Really useful script, thanks for sharing! I've made a little addition to include TCP states, if anyone cares: https://gist.github.com/qistoph/1b0708c888f078c3720de6c6f9562997

I appreciate both of your work!

I updated to make it a little easier to reuse:
https://gist.github.com/petermueller/1b837eddc443857b2051f739818cfad7