Search/Grep only Public IP Address with Regex in Linux

Question

I've been reading about Regex to ONLY match PUBLIC IPv4 address and tried all solution given, but none of them actually can match the Public IP Address accurately.

Sample IP

[user@linux ~]$ cat ip.txt
1.1.1.1
8.8.8.8
10.1.1.1
127.0.0.1
[user@linux ~]$

Solution 1 - https://stackoverflow.com/a/39195704/11392987

[user@linux ~]$ egrep '^([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])(?<!172\.(16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31))(?<!127)(?<!^
10)(?<!^0)\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])(?<!192\.168)(?<!172\.(16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31))\.([0-9]|[1-
9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])(?<!\.255$)$' ip.txt
[user@linux ~]$

Sol 2 - https://stackoverflow.com/a/33453740/11392987

[user@linux ~]$ egrep '(\d+)(?<!10)\.(\d+)(?<!192\.168)(?<!172\.(1[6-9]|2\d|3[0-1]))\.(\d+)\.(\d+)' ip.txt
[user@linux ~]$

Sol 3 - https://stackoverflow.com/a/46399203/11392987

[user@linux ~]$ egrep '(^0\.)|(^10\.)|(^100\.6[4-9]\.)|(^100\.[7-9]\d\.)|(^100\.1[0-1]\d\.)|(^100\.12[0-7]\.)|(^127\.)|(^169\.254\.)|(^172\.1[6-
9]\.)|(^172\.2[0-9]\.)|(^172\.3[0-1]\.)|(^192\.0\.0\.)|(^192\.0\.2\.)|(^192\.88\.99\.)|(^192\.168\.)|(^198\.1[8-9]\.)|(^198\.51\.100\.)|(^203.0\
.113\.)|(^22[4-9]\.)|(^23[0-9]\.)|(^24[0-9]\.)|(^25[0-5]\.)' ip.txt
10.1.1.1
127.0.0.1
[user@linux ~]$

10.1.1.1 & 127.0.0.1 are Private IP Address, not Public IP

Sol 4 - https://stackoverflow.com/a/57077560/11392987

[user@linux ~]$ egrep '^(?!^0\.)(?!^10\.)(?!^100\.6[4-9]\.)(?!^100\.[7-9]\d\.)(?!^100\.1[0-1]\d\.)(?!^100\.12[0-7]\.)(?!^127\.)(?!^169\.254\.)(?
!^172\.1[6-9]\.)(?!^172\.2[0-9]\.)(?!^172\.3[0-1]\.)(?!^192\.0\.0\.)(?!^192\.0\.2\.)(?!^192\.88\.99\.)(?!^192\.168\.)(?!^198\.1[8-9]\.)(?!^198\.
51\.100\.)(?!^203.0\.113\.)(?!^22[4-9]\.)(?!^23[0-9]\.)(?!^24[0-9]\.)(?!^25[0-5]\.)(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-
9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]))$' ip
.txt
[user@linux ~]$

Sol 5 - https://www.bigdatamark.com/regexp-for-extracting-public-ip-address/

[user@linux ~]$ egrep '\b(?!(10)|192\.168|172\.(2[0-9]|1[6-9]|3[0-2]))[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' ip.txt
[user@linux ~]$

Answer 1

The real question is why does it have to be one single regex?

If the input is validated a simpler regex can be achieved, by validated I mean there is no out of bounds ip addresses in the input. If so something like this could work.

grep "\([0-9]\{1,3\}\.\)\{3\}[0-9]\{1,3\}" ip.txt | 
grep -v "10\(\.[0-9]\{1,3\}\)\{3\}\|192\.168\(\.[0-9]\{1,3\}\)\|172\.\(1[6-9]\|2[0-9]\|3[01]\)\.[0-9]\{1,3\}\.[0-9]\{1,3\}\|127.0.0.1"

if validation is required than the regex gets much more complicated

grep  "\([0-9]\.\|[1]\{,1\}[0-9]\{2\}\.\|2[0-4][0-9]\.\|25[0-5]\.\)\{3\}\([0-9]\|[1]\{,1\}[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)" ip.txt |
grep -v "10\(\.[0-9]\|\.[1]\{,1\}[0-9]\{2\}\|\.2[0-4][0-9]\|\.25[0-5]\)\{3\}" |
grep -v "172\.\(1[6-9]\|2[0-9]\|3[01]\)\.\([0-9]\.\|[1]\{,1\}[0-9]\{2\}\.\|2[0-4][0-9]\.\|25[0-5]\.\)\([0-9]\|[1]\{,1\}[0-9]\{2\}\|2[0-4][0-9]\|25[0-5]\)" |
grep -v "192.168\(\.[0-9]\|\.[1]\{,1\}[0-9]\{2\}\|\.2[0-4][0-9]\|\.25[0-5]\)\{2\}" |
grep -v "127.0.0.1"

I split up the 3 classes of private ip address spaces, with each another piped grep command for simplicity you could join them all with a

\|

and have only the two grep commands.

Answer 2

Try this regex. It matches all public IPs and doesn't match reserved IPs.

Edit - Try using grep -P instead of egrep because egrep doesn't support lookahead.

grep -P '^(?!^0\.)(?!^10\.)(?!^100\.6[4-9]\.)(?!^100\.[7-9]\d\.)(?!^100\.1[0-1]\d\.)(?!^100\.12[0-7]\.)(?!^127\.)(?!^169\.254\.)(?!^172\.1[6-9]\.)(?!^172\.2[0-9]\.)(?!^172\.3[0-1]\.)(?!^192\.0\.0\.)(?!^192\.0\.2\.)(?!^192\.88\.99\.)(?!^192\.168\.)(?!^198\.1[8-9]\.)(?!^198\.51\.100\.)(?!^203.0\.113\.)(?!^22[4-9]\.)(?!^23[0-9]\.)(?!^24[0-9]\.)(?!^25[0-5]\.)(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5]))$' ip.txt

Output

1.1.1.1
8.8.8.8