Bash while read loop breaking early [duplicate]

Answer 1

talk about a "robbing Peter to pay Paul" problem. I'd been struggling for hours to figure out why my ssh was killing my something|while read loop.

Another way to stick with a while read loop and keep your ssh at the same time is to use the "-n" switch to make STDIN on ssh /dev/null. Works like a charm for me:

#!/bin/bash
[...]
something|while read host
   do
      ssh -nx ${host} fiddleAround
   done

(I tend to always use the "-x" too to avoid wasting time negotiating X in a tunnel.)

Answer 2

In the construct

something | 
while read x; do 
    ssh ...
done

the standard input as seen by the while loop is the output of something.

The default behavior of ssh is to read standard input. This allows you to do things like

cat id_rsa.pub | ssh new_box "cat - >> ~/.ssh/authorized_keys"

Now, with that being said, when the first value is read, the first ssh command will read the entire input from something. Then, by the time ssh finishes, there is no output left, and read stops.

The fix is ssh -n ... e.g.

cat /etc/hosts | awk '{print $2}' | while read x; do
    ssh -n $x "do_something_on_the_machine"
done

Answer 3

As Kaii mentioned, it's really overkill to call ruby or seq (which won't work on BSD or OSX machines) just to output a range of numbers. If you're happy with using bash you can:

for i in {0..20}; do
    # command
done

I believe this should work for bash 2.05b and up.