Grabbing variables and comparing

Thread Tools Search this Thread
Top Forums Shell Programming and Scripting Grabbing variables and comparing
# 1  
Old 08-17-2008
Grabbing variables and comparing

I have two computers with dynamic IP addresses and am using dyndns so that they are identifiable as the same computer even if their IPs change (we'll call them and I also have a remote server which I would like to store my computers' IP addresses on. There is a file on my remote server which has the IPs that the two hostnames point to. So the file would look like this

I need a script that will run this command which gets the IPs of my computers:

/usr/bin/dig +short | /usr/bin/tail -n 1
/usr/bin/dig +short | /usr/bin/tail -n 1

Then compare the result (which is an IP address) to the file that I have described above. If the IP is different from the old one then remove that line and replace it with the new IP. I thought I could do this myself but grabbing the old IP and storing it in a variable and then comparing it to the new IP was beyond me. I don't even know if that is how you should do it. sed/awk is preferable but any language will do Smilie

Thanks in advance.
# 2  
Old 08-17-2008
perl -pe 'use Socket; /(\d+.\d+.\d+.\d+)\s#(.*?)\s*$/; $dig=inet_ntoa(inet_aton($2)); s/$1/$dig/ if ($dig ne $1);' FILE > && mv FILE

FILE is where you have the old addresses. You must change that in order for this to work.
# 3  
Old 08-17-2008

Thanks. I need to run the script on the remote server and find the IP addresses of my home computers with dynamic IPs. I'm not sure if that is what the script is doing b/c it looks very complex and I don't really understand everything. In any event, ran the script and I got this error:

Bad arg length for Socket::inet_ntoa, length is 0, should be 4 at -e line 1, <> line 1.

Thanks again and thanks in advance if anyone else takes a crack at this.
# 4  
Old 08-17-2008
Originally Posted by kerpm
Bad arg length for Socket::inet_ntoa, length is 0, should be 4 at -e line 1, <> line 1.
That's because your host's file has an empty line. "next unless" will solve that. Keep in mind that the host's file has to have always something like ip #hostname for this to work.

perl -pe 'use Socket; next unless /(\d+.\d+.\d+.\d+)\s#(.*?)\s*$/; $dig=inet_ntoa(inet_aton($2)); s/$1/$dig/ if ($dig ne $1);' FILE > && mv FILE

Tsunami comparing # cat ips
Tsunami comparing # perl -pe 'use Socket; next unless /(\d+.\d+.\d+.\d+)\s#(.*?)\s*$/; $dig=inet_ntoa(inet_aton($2)); s/$1/$dig/ if ($dig ne $1);' ips
Tsunami comparing #

# 5  
Old 08-17-2008
An approach with awk:

awk -F"#" 'BEGIN{
"/usr/bin/dig +short | /usr/bin/tail -n 1" |getline ip[""]
"/usr/bin/dig +short | /usr/bin/tail -n 1" |getline ip[""]}
$2 in ip{$0=ip[$2]" #"$2}
{print}' file > new_file

# 6  
Old 08-17-2008
redoubtable, you are the man. It works perfectly Smilie
# 7  
Old 08-17-2008
Franklin52. Thank you as well! I appreciate all the help I've received on this forum Smilie
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. UNIX for Beginners Questions & Answers

Comparing 2 variables in UNIX

Hi, I have 2 variables as given below. How can i compare them and say its matching ? Appreciate your help VAR1=describe/read/write VAR2=read/write/describeThanks, Please use CODE tags as required by forum rules! (4 Replies)
Discussion started by: prince1987
4 Replies

2. Shell Programming and Scripting

Grabbing text between two lines with shell variables.

I would like to grab complex html text between lines using variables. I am running Debian and using mksh shell. Here is the part of the html that I want to extract from. I would like to extract the words 'to love,' and I would like to use the above and below lines as reference points. ... (3 Replies)
Discussion started by: bedtime
3 Replies

3. Shell Programming and Scripting

Comparing two variables

I have a script like this. Just couldn't get the comparison part work. Any thought? thanks, #!/usr/bin/ksh -x STEP=`echo $(basename $0 .ksh) | tr "" ""` log=/skip.log while read LINE do if then echo `date`: STEP $STEP skipped by user >> $log exit 0 fi done < $1 echo... (0 Replies)
Discussion started by: ghostmic
0 Replies

4. Shell Programming and Scripting

awk comparing variables

Is there a way to compare variables in a 'awk'? I've been trying for a while and can't figure it out. I'm guessing its not possible :/ VAR=Bob awk '$3 == $VAR { print $1 }' file.txt Regards Jikuu (4 Replies)
Discussion started by: Jikuu
4 Replies

5. Shell Programming and Scripting

comparing variables in an if statement

#!/bin/bash #timetest TIMENOW="$(date)" T1=12:00:00 echo $TIMENOW >timenow cat timenow |cut -f4 -d' ' >time1 T2=$(sed -n "${1}p" time1) echo "T1 = " $T1 echo "T2 = " $T2 if then echo $T1 else echo $T2 fi I thought scripting was simple! So why does this script result in: T1 =... (4 Replies)
Discussion started by: habuchas
4 Replies

6. Shell Programming and Scripting

Comparing multiple variables

Hi! I've come up with a ksh-script that produces one or more lists of hosts. At the and of the script, I would like to print only those hosts that exists in all the lists. Ex. HOSTS="host1 host2 host3 host11" HOSTS="host1 host2 host4" HOSTS="host2 host11" HOSTS="host2 host5 host6 host7... (1 Reply)
Discussion started by: Bugenhagen
1 Replies

7. UNIX for Dummies Questions & Answers

comparing variables

im trying to compare ipaddresses. i loop through an array to see if the ip is already is in the array and if it is it should set a flag and then i wont add it to the array. but its just adding all the ipaddresses to the array if ] then ... (3 Replies)
Discussion started by: magnia
3 Replies

8. Shell Programming and Scripting

Comparing Variables in Perl

Hi. I have three arrays. @a=('AB','CD','EF'); @b=('AB,'DG',HK'); @c=('DD','TT','MM'); I want to compare the elements of the first two array and if they match then so some substition. I tried using the if statement using the scalar value of the array but its not giving me any output. ... (7 Replies)
Discussion started by: kamitsin
7 Replies

9. Shell Programming and Scripting

Comparing two variables

Script #!/bin/sh hardware=PC os=WindowsNET for i in `cat newservers` do x=`sudo /opt/openv/netbackup/bin/admincmd/bpplclients |grep $i |head -40 |grep $i|awk '{print $3;exit}'` if then echo "$i is already added" else echo "Need to add" fi done O/p in debug mode bash-2.05$... (3 Replies)
Discussion started by: rajip23
3 Replies

10. UNIX for Dummies Questions & Answers

comparing variables

I have searched and found a few threads that have dealt with this, but the examples I've tried haven't seemed to help. I am monitoring our database log for high checkpoints. I can parse out the checkpoint value which can be anywhere from zero into a 3 digit number. I set a variable to be the... (3 Replies)
Discussion started by: MizzGail
3 Replies
Login or Register to Ask a Question

Featured Tech Videos