Bash while read loop breaking early [duplicate]

Answer 1

Most of the answers are specific to ssh. Other commands also hijack stdin and do not have a -n option. This should address any other commands. This should also work for ssh.

while read x; do 
    # Make sure command does not hijack stdin
    echo "" | command $x
done < /path/to/some/file

Answer 2

Chris is correct. The source of the loop breaking was SSH using stdin, however guns is correct in is usage of a looping methodology.

If you are looping through input (a file with a list of hostnames for example), and calling SSH, you need to pass the -n parameter, otherwise your loop based on input will fail.

while read host; do
  ssh -n $host "remote command" >> output.txt
done << host_list_file.txt

Answer 3

I'm also unsure about why it fails, but i like xargs and seq:

seq 0 20 | xargs -n1 tssh MYBOXES

Answer 4

i cant believe it was the result of 0 that broke your loop, you can test against this by replacing your tssh command in the loop with "/bin/true" which also returns 0.

regarding style i dont understand why a simple looping shell script needs ruby, perl, seq or jot or any other binary that is not on my *BSD.

you can alternatively use the shells builtin for loop construct, which works at least in ksh, bash:

for ((i=0; $i<=20; i++)); do
    tssh "MYBOXES$i"
done

Answer 5

Don't know if it would help, but a cleaner way of writing that would be

for nu in `ruby -e '(0..20).each { |i| puts i}'`; do
  tssh "MYBOXES$nu" 
done

Answer 6

I ran into this today -- rsh and/or ssh can break a while read loop due to it using stdin. I put a -n into the ssh line which stops it from trying to use stdin and it fixed the problem.