change of ip address using perl or sed

Question

I've an input file that consists of IP Address and subnet masks. As an example,

1.example.com,10.135.10.111,255.255.255.0,some comment
2.example.com,10.135.10.112,255.255.255.0,some comment
3.example.com,10.135.10.113,255.255.255.0,some comment
4.example.com,10.135.10.11,255.255.255.0, some comment
10.135.10.111 A 
10.135.10.112 A
10.135.10.113 A
10.135.10.11  A

I loop the IP address in my bash script and when using the perl or sed command all .11 gets changed. As an example:

inputip=10.135.10.11
newip=10.135.10.77

perl -i -e 's/$inputip/$newip/g' inputfile

OR

sed -e "s/$inputip/$newip/g" inputfile

The problem is all instance of .11 gets changed. so the above record of 10.135.10.111 is changed to 10.135.10.771, .772, .773, .77

Note: this line 10.135.10.11 A is not necessarily the last line, it's anywhere in the file.

Answer 1

There are four problems with the Perl version.

• You're missing -p.

• You expected Perl to use the shell variables $inputip and $newip, but those are only found in the shell process. There's a number of ways to pass values to perl, as you can see in How can I process options using Perl in -n or -p mode?.

• There's also a code injection bug, where . isn't matched literally.

• There's an anchoring problem, where you accidentally modify IP addresses you don't want to change. For example, you will corrupt 210.135.10.11 when trying to change 10.135.10.11.

Fixed:

perl -i -spe's/\b\Q$o\E\b/$n/g' -- -o="$inputip" -n="$newip" inputfile

Answer 2

Input:

$ cat inputfile
1.example.com,10.135.10.111,255.255.255.0,some comment
2.example.com,10.135.10.112,255.255.255.0,some comment
3.example.com,10.135.10.113,255.255.255.0,some comment
4.example.com,10.135.10.11,255.255.255.0, some comment
4.example.com,210.135.10.11,255.255.255.0, some comment
10.135.10.111 A
10.135.10.112 A
10.135.10.113 A
10.135.10.11  A
210.135.10.11 A

With GNU sed and word boundary sequences (\< / \>):

$ inputip=10.135.10.11
$ newip=10.135.10.77
$ sed "s/\<$inputip\>/$newip/g" inputfile
1.example.com,10.135.10.111,255.255.255.0,some comment
2.example.com,10.135.10.112,255.255.255.0,some comment
3.example.com,10.135.10.113,255.255.255.0,some comment
4.example.com,10.135.10.77,255.255.255.0, some comment
4.example.com,210.135.10.11,255.255.255.0, some comment
10.135.10.111 A
10.135.10.112 A
10.135.10.113 A
10.135.10.77  A
210.135.10.11 A

If this does not work then OP is likely not using GNU sed; in this case we'd need to know what version of sed is in use (eg, sed --version).