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

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jpgxs commented Aug 4, 2019

Don't forget about ss

@egorky

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egorky commented Oct 27, 2019

this was useful to me because in some docker containers there's no ss nor netstat

@josephmate

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josephmate commented Oct 28, 2019

My docker container did not come with and of the tools recommended when you google for listening ports: netstat, ss, lsof, or nmap. Copying and pasting the all in one after running docker exec -it /bin/bash worked. I was able to diagnose my problem as result. Thank you!

@bappr

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bappr commented Apr 8, 2020

Awesome sauce.
Thanks for sharing!

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