Hi Darren, I got it. Many thanks for your excellent explanations. Best regards, Jin On Tue, Oct 18, 2016 at 2:04 PM, Darren Tucker <dtucker@xxxxxxxxxx> wrote: > On Tue, Oct 18, 2016 at 10:34 AM, Jin Li <lijin.abc@xxxxxxxxx> wrote: >> Could you tell me why `stdin` needs to be overwritten in SSH? Thanks. > > Consider this (almost) equivalent simplified script: > > while read -r run > do > ssh localhost date > done < <(seq 10) > > What's happening is that the remaining 9 lines are being read by ssh > and sent to the remote server where the "date" command ignores them > and they are discarded (but ssh doesn't know that the remote "date" is > going to do that). If you replace the "date" with "cat" you can see > this: > > $ cat t > while read -r run > do > cat > done < <(seq 10) > > $ bash t > 2 > 3 > 4 > 5 > 6 > 7 > 8 > 9 > 10 > > This doesn't happen with a local "date" command because it never reads > its stdin. > > When you redirect ssh's stdin to /dev/null the ssh no longer consumes > the output from "seq". ssh also has a "-n" option that does this. > > -- > Darren Tucker (dtucker at zip.com.au) > GPG key 11EAA6FA / A86E 3E07 5B19 5880 E860 37F4 9357 ECEF 11EA A6FA (new) > Good judgement comes with experience. Unfortunately, the experience > usually comes from bad judgement. _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
