Shell Programming and Scripting

Hi,

I have a file which keeps on appending the data continuously, i that i am looking for a particular pattern, if i dont find that pattern i want to wait for 30 seconds to check it again.

can we use it like this
-----------------------------
until [ $? -eq "0" ]
do

cat $line | tail -5 | grep 'PATTERN' > /dev/null

sleep 30
done

echo "File Contains the pattern 'PATTERN' now"
------------------------------------------------------
i am not able to get it, even if pattern is not there it is coming out of loop and executing echo command in any case.

Can someone plesae help me on this

thanks in advance

First off, you should post ALL of the code, not just a snippet of the until loop. Based on your post, I have no clue what "$line" is.

Second, please use the code box/tags for your code...thats the little "#" icon near the top right of the toolbar when you are making a post.

Third, the reason that your loop is exiting is that "$?" was 0 when you started the loop. Its kinda like saying this:

Code:

until [ 1 -eq 1 ]; do
    ./stuff
done

the command ./stuff will never run.and even if "$?" was not 0 to start off the loop, the "sleep 30" command would certainly have a 0 exit status.

So, what you probably want to do is something like this:

Code:

until cat $line | tail -5 | grep 'PATTERN' > /dev/null 2&>1; do
    sleep 30
done

echo pattern PATTERN found

You do not really have to do a test/comparison (i.e. [ 1 -eq 1 ]) with a while, or until loop, as it just evaluates the exit status of the command after "until". Believe it or not, the square bracket comparison is actually a command (its the "test" command).