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I need to put the IP of my VPS machine into a variable. I mean to the external IP address appearing the value of inet addr section, in ifconfig output.

I've tried:

ipa="$(hostname -i)"

But echo ${ipa} brought the localhost token: 127.0.1.1, so I looked for other solutions and all I found includes many pipes and awk operations which I know nothing about (never used awk and I'm not very familiar with regex).

I tried this:

ipa=$(ifconfig | grep "inet addr:[0-999]\.[0-999]\.[0-999]\.[0-999]")

But it failed given that echo ${ipa} has an empty line of output.

Why did what I've tried failed or at least how would you solve it?

  • It is most important for me to understand what why I tried failed (please review my question edit). –  Dec 12 '17 at 12:25

2 Answers2

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ipa=$(ifconfig | perl -lane '/inet addr:(\S+)/ and $1 !~ "^127" and print $1')

Also see here for a plethora of alternatives. E.g. using grep:

ipa=$(ifconfig | grep -Po 'inet addr:\K[^\s]+' | grep -v '^127')

Explanation:

ipa=$( ) assign the output of the command in parentheses to the variable ipa
ifconfig show interfaces and their addresses. You might prefer ip address
| grep -Po 'inet addr:\K[^\s]+' filter output using a perl-compatible regex, print the matched text
| grep -v '^127' filter again, this time excluding (-v) values that start (^) with 127

To get my external ip, I usually do:

dig +short myip.opendns.com @resolver1.opendns.com
simlev
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  • So sad I don't know perl so at the moment feel uncomfortable to use it (I don't want to use something I don't understand well enough, usually). What do you think on my approach? –  Dec 12 '17 at 11:43
  • @Benia This perl code is quite simple, but if you feel uncomfortable then by all means don't use it! Or learn perl! Or pick any of the several methods from the linked answers. I added a grep alternative, since you already tried with grep. – simlev Dec 12 '17 at 11:52
  • I've tried my example only now with echo in the end but the output line is empty --- my grep failed. –  Dec 12 '17 at 12:01
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grep "inet addr:[0-999]\.[0-999]\.[0-999]\.[0-999]"

That would match the string inet addr: followed by a single character that is a digit from 0 to 9, or a 9, or a 9, followed by a dot, then another character that is 0 to 9 or 9 or 9... e.g. inet addr:1.2.3.4, but not inet addr:11.22.33.44.

Bracket groups don't match strings that form numbers, just single characters.

ilkkachu
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  • Additionally, even if it worked, it's going to return the entire line, containing inet addr: ....... not just the IP address. – EightBitTony Dec 12 '17 at 13:31
  • @EightBitTony this is because I didn't wrap the bracket gripus in parenthesis? –  Dec 12 '17 at 13:42