Using sed to search and replace an ip address in a file

Question

Been trying to get this working for a while and not really quite getting it. Basically, I have a file with an ip address that changes more or less on a daily basis. The file only contains one ip address and this is the one I'm trying to replace with my crazy grepping to find my current internal ip.

I have this

#!/bin/sh

newip=$(ifconfig | grep 0xfff | grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' | grep -v 255)

echo $newip
sed 's/*\.*\.*\.*/"$newip"/g' log.txt > logmod.txt

but it's not matching and replacing. I'm not familiar with sed and I am a beginner with regexps too.

Any help would be awesome! Thanks :)

Solution 1

If your version of sed supports extended regular expressions (the -r option), you could do something like this (which is similar to what you have in your grep statement). Also note $newip is outside the single quotes to allow the shell to replace it.

sed -r 's/(\b[0-9]{1,3}\.){3}[0-9]{1,3}\b'/"$newip"/

BTW this solution still matches strings that do not represent IP addresses. See this site under IP Adresses for more complex solutions.

Solution 2

sed -e 's/old ip/new ip/g' filename

Solution 3

IP=207.0.0.2; [[ x${IP}x =~ x"(2([0-4][0-9])|2(5[0-5])|1[0-9][0-9]|[1-9][0-9]|[0-9])\.(2([0-4][0-9])|2(5[0-5])|1[0-9][0-9]|[1-9][0-9]|[0-9])\.(2([0-4][0-9])|2(5[0-5])|1[0-9][0-9]|[1-9][0-9]|[0-9])\.(2([0-4][0-9])|2(5[0-5])|1[0-9][0-9]|[1-9][0-9]|[0-9])"x ]] && echo ok || echo bad

this validates only four decimal octet representation so this one will fail 016.067.006.200 (even valid but not four decimal octet representation, but octal)

016.067.006.200 =~ 14.55.6.200

Comments

[Steve Emmerson]

Be advised that the "\b" (word boundary) construct isn't standard.

[heijp06]

@Steve: That's true. I tested the expression with GNU sed version 4.2.1. Since the OP added the bash tag I assumed he might have some version of GNU sed as well. Also note that I specifically mention the -r option.

[twistedpixel]

You, my friend, have saved me so many hours of stress! My version of sed did not unfortunately support -r so I used homebrew (I'm using a Mac) and installed the latest version which worked perfectly!

[tripleee]

Surely the OP wants the replacement to be the value of a variable, not the static text NEW_IP. The single quotes inhibit variable interpolation, and anyway, the existing answers already cover this.

[Martin Gal]

Please don't simply post code. Add some context to your answer. Take a look at How to answer