Shell Programming and Scripting

Hi Everyone,

Can someone please show me how to create a script that will search a text file for changes.

For example below is a sample of how the text file would look like,

RLH rlh-1 ALIVE 20:06:05
RLH rlh-7 ALIVE 20:06:05
RLH rlh-3 ALIVE 20:06:05
RLH rlh-2 ALIVE 20:06:05

I would like the script to alert me on screen when the "ALIVE" word for a particular line say rlh-1 changes to something else.

Thanks a lot.

Hello
you can create a backup of your existing file. can you use "diff" in a cron job to check the file against the backup file. If there is some difference then the cron print to say your mailbox a diagnostic message. After the change you can mv current_file backup_file to see further changes.
Regards.

Code:

cp file file.backup

cron job

Code:

#!/usr/local/bin/perl
use strict;
use warnings;
my @arr=`diff /path/to/file /path/to/file.backup`;   #store the difference of lines
if(@arr) {foreach (0..$#arr)                                  #check if the difference exists
{print $arr[$_];} 
my$res=`mv /path/to/file /path/to/file.backup`}      #change the backup file to be the current file (if wanted,otherwise not)

Regards.

Thank you gaurav1086,

The script below may help explain what I have in mind.

The if statement is supposed to check whether the output equals the string "$ALIVE" and if it does not, then display the string "RLH -1 service is not running"

Obviously it does not work because it is giving me the error below

awk: cmd. line:1: fatal: cannot open file `==' for reading (No such file or directory)

Please advice.

Perhaps the following will suit your needs:

Code:

if ! awk '$2=="rlh-1" && $3!="ALIVE" {exit 1}' chkstat.txt; then
    echo "RLH -1 service is not running"
    echo "$beep"
fi

why not this.

Code:

  awk -v ALIVE=$var '$4!=$ALIVE{system("echo $beep");print "RLH-1 service is not running"}' in_file

where $var is the shell variable that you want to pass.
Regards.

Hi, guarav1086:

From kumaran21's original post and the later post's grep, it seems that a specific line's status is being tested (in the sample data provided, those with $2="rlh-1"). Your code will trip on any.

Unless it's being exported into the environment, $beep will be undefined when awk executes a subshell to run "echo $beep" (running a shell to simply echo is rather wasteful; awk's print statement will do). $beep is also undefined within the scope of the awk script, but it can be properly passed in via -v on the command line or expanded by the shell itself before invoking awk if the quoting is adjusted.

I don't think parameterizing the "ALIVE" field would be as useful as the "rlh-??", but I can't say since i don't know exactly how the script will be put to use.

Take care,
alister

Hello alister,
He mentioned to test $4(field) so I dint consider other field as I do not know about the script being affected by other parameters.. I agree $beep would not produce any significant result. But I guess $beep is not an "alarm" . I guess he has mentioned it to signify that some handler is to be invoked in respose to this event, but I am not sure. Again if its not like that , then $beep can be very well passed as "-v" parameter. Anyways, thanks for pointing it out.
Regards
Gaurav.