Why is this while loop not looping? - bash

Question

I have the following bash script deploy.sh:
#!/usr/bin/env bash
# Some useful resources:
# while read ip user pass; do : http://unix.stackexchange.com/questions/92664/how-to-deploy-programs-on-multiple-machines
# -o StrictHostKeyChecking=no: http://askubuntu.com/questions/180860/regarding-host-key-verification-failed
# -T: http://stackoverflow.com/questions/21659637/how-to-fix-sudo-no-tty-present-and-no-askpass-program-specified-error
# echo $pass |: http://stackoverflow.com/questions/11955298/use-sudo-with-password-as-parameter
while read ip user pass; do
echo $ip
sshpass -p "$pass" ssh $user#$ip -o StrictHostKeyChecking=no -T "
echo 'yo'
"
echo 'done'
done < servers.txt
servers.txt contains:
53.12.45.74 my_username my_password
54.12.45.74 my_username my_password
57.12.45.74 my_username my_password
‌‌
From my understanding, the while read ip user pass; do […] done < servers.txt should loop over all three lines of servers.txt.
However, when I try to run it, it only performs one iteration:
ubuntu#server:~$ bash deploy.sh
53.12.45.74
yo
done
ubuntu#server:~$
Why?
If the loop is simply:
while read ip user pass; do
echo $ip
done < servers.txt
it does perform all three iterations:
ubuntu#server:~$ bash deploy.sh
53.12.45.74
54.12.45.74
57.12.45.74
ubuntu#server:~$

Answer 1

sshpass is taking control of stdin or possibly replacing it and causing while loop to lose input from redirected stdin.
To work around this issue, avoid reading from stdin.
First, load the file into an array using a while loop.
while read line; do
entries+=("$line")
done < servers.txt
Next, use for loop to parse the lines and execute sshpass within this loop.
for line in "${entries[#]}"; do
set $line
ip=$1
user=$2
pass=$3
echo $ip
sshpass -p "$pass" ssh $user#$ip -o StrictHostKeyChecking=no -T "
echo 'yo'
"
echo 'done'
done
The second loop doesn't read from stdin.
But I will recommend Rany Albeg Wein answer using a separate descriptor than the current stdin.
while read ip user pass <&3; do
echo $ip
sshpass -p "$pass" ssh $user#$ip -o StrictHostKeyChecking=no -T "
echo 'yo'
"
echo 'done'
done 3<servers.txt

Answer 2

#!/usr/bin/env bash
# Some useful resources:
# while read ip user pass; do : http://unix.stackexchange.com/questions/92664/how-to-deploy-programs-on-multiple-machines
# -o StrictHostKeyChecking=no: http://askubuntu.com/questions/180860/regarding-host-key-verification-failed
# -T: http://stackoverflow.com/questions/21659637/how-to-fix-sudo-no-tty-present-and-no-askpass-program-specified-error
# echo $pass |: http://stackoverflow.com/questions/11955298/use-sudo-with-password-as-parameter
while read ip user pass; do
if [ -n "$ip" ]; then
echo "IP[$ip] USER[$user] PASS[$pass]";
# dont forget to uncomment this two lines here:
#sshpass -p "$pass" ssh $user#$ip -o StrictHostKeyChecking=no -T "
#echo 'yo'
echo ""; # Just a blank line"
echo "done.";
else
echo "Empty value.";
fi
done < servers.txt
So, now it works.