problem in while loop

The problem is that ssh reads standard input when it runs, so takes all of the "while read" loop's input lines.

Add the "-n" option to stdin, to stop it reading all standard input.

From my reading of the ssh man page, I wonder whether -n is really what you want.
If it works for you that's great; otherwise you could have better luck using a here document.
I experimented with cat, which also reads stdin if you don't give it any arguments

$ (cat <<////
> abcd
> ////
> )|rev
dcba
$ 

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You have to run ssh (instead of cat) in a subshell (enclose in parentheses), because the document terminator has to appear on a line by itself (you can't put any other character after it). You can see that the pipe worked because rev has reversed the entered input. Here's how I suggest your line should look

b=`(ssh amzphxjethro05 <<//// 
zcat /md1/dev-scripts/PTD-Jethro-Stage/DSI_BC/${line} |wc -l
////
)`

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You want to put a matching backtick after the terminator, so I think you need to run in a subshell. You no longer need all the quoting you used to have though.

Hi Duncan, I would normally suggest adding
    </dev/null
to the command within a "while" loop, but ssh supports "-n" for that very purpose, which is neater.

Or rather

whatever =`ssh -n host sh -c "\"zcat ...| wc \""`

... so the wc is run on the remote host. Otherwise you are sending the whole output of zcat over the network

Similarly

X=`ssh hostname sh -s`<<EOF
  zcat whatever | wc whatever
EOF

Should do the trick

I believe the latter is easier to read

@sai niharika sariputi

1. I used following code as per first comment from simon3270 using -n option
Using $() instead of ``
Using sed to remove all characters excluding number at Linux system here

#!/bin/bash
if [ -f /usr/local/apps/jethro/devl/bin/file_names.txt ]
then
        /usr/bin/cat /usr/local/apps/jethro/devl/bin/file_names.txt|while read -r line;
        do
                if [[ ${line} == DSI_BC_DIM* ]];
                then
                        echo "DIM line: $line"
                        #Using /usr/bin/sed to remove all characters and assign only wc -l number alone to variable b
                        b=$(echo -e $(/usr/bin/ssh -n amzphxjethro05 'zcat /md1/dev-scripts/PTD-Jethro-Stage/DSI_BC/'"${line}"' | /usr/bin/wc -l') | /usr/bin/sed "s/.*\a//;")
                        echo "b: ${b} "
                        /usr/bin/expr "${b}" - 1
                        echo "-----------------"
                else
                        echo "working line: ${line}"
                        b=$(/usr/bin/ssh -n amzphxjethro05 'zcat /md1/dev-scripts/PTD-Jethro-Stage/DSI_BC/'"${line}"' | /usr/bin/wc -l')
                        echo "b: ${b} "
                        echo "-----------------"
                fi
        done
else
        echo "/usr/local/apps/jethro/devl/bin/file_names.txt file not found"
fi

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ONE MORE WAY:
2. Without using -n option using for loop
Using $() instead of ``
Using sed to remove all characters excluding number at Linux system here

#!/bin/bash
if [ -f /usr/local/apps/jethro/devl/bin/file_names.txt ]
then
        for LINE in $(/usr/bin/cat /usr/local/apps/jethro/devl/bin/file_names.txt)
        do
                if [[ ${LINE} == DSI_BC_DIM* ]];
                then
                        echo "DIM LINE: $LINE"
                        #Using /usr/bin/sed to remove all characters and assign only wc -l number alone to variable b
                        b=$(echo -e $(/usr/bin/ssh amzphxjethro05 'zcat /md1/dev-scripts/PTD-Jethro-Stage/DSI_BC/'"${LINE}"' | /usr/bin/wc -l') | /usr/bin/sed "s/.*\a//;")
                        echo "b: ${b} "
                        /usr/bin/expr "${b}" - 1
                        echo "-----------------"
                else
                        echo "working LINE: ${LINE}"
                        b=$(/usr/bin/ssh amzphxjethro05 'zcat /md1/dev-scripts/PTD-Jethro-Stage/DSI_BC/'"${LINE}"' | /usr/bin/wc -l')
                        echo "b: ${b} "
                        echo "-----------------"
                fi
        done
else
        echo "/usr/local/apps/jethro/devl/bin/file_names.txt file not found"
fi

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you are sending the whole output of zcat over the network and counting lines locally.
this is highly inefficient : you need to execute the wc remotely.

likewise, there is no point in spawning one ssh command per file

>> there is no point in spawning one ssh command per file
yes
we agree and it varies based on requirement, design document, ... :

for remoteHOSTIP in ...
do
...
for LINE in
...
.../usr/bin/ssh ... $remoteHOSTIP
done
...
done

yep. feel free to provide the corrected script. but you may notice the thread has been dead for about 6  months. i won't bother.

>> the thread has been dead for about 6  months
Thank you for the comments.
@sai niharika sariputi
if required, we will post updated script (based on your requirements and given files)