Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.debian.user > #263778

bash vs. dash and stdin

Show all headers | View raw

Hi,

There was a thread on stdio buffering and fork a month ago. That time I 
thought shells should be rather careful with input/output handling when 
spawning subprocesses.

Consider a file (ssh.sh) containing a couple of commands:

    ssh localhost echo remote
    echo local

Let's try to run it (assuming key-based authorization)

     bash <ssh.sh
     remote

One might expect to see "local" as well.

     dash <ssh.sh
     remote
     local

Is there a document that describes shell behavior in respect to stdin in 
such cases?

If the script is passed as an argument, not to stdin, then output 
contains "local" in both cases. I admit that ssh (called this way) can 
not avoid consuming of some stdin, so bash behavior may be considered a 
bit more correct despite initial expectations.

If you are going to try strace then, to make difference more prominent, 
it is better to force creation of a pipe

     cat ssh.sh | strace bash

I am curious if it may be a dash bug or it is just falls into the 
category of unspecified behavior.

P.S. I noticed it in a discussion whether a command not executed after 
ssh is an Emacs bug. My conclusion is that "ssh -n" should be used in 
scripts unless a remote command really needs stdin.

Back to linux.debian.user | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

bash vs. dash and stdin Max Nikulin <manikulin@gmail.com> - 2023-11-22 13:10 +0100
  Re: bash vs. dash and stdin Greg Wooledge <greg@wooledge.org> - 2023-11-22 13:20 +0100
    Re: bash vs. dash and stdin Max Nikulin <manikulin@gmail.com> - 2023-11-23 12:10 +0100
  Re: bash vs. dash and stdin Nicolas George <george@nsup.org> - 2023-11-22 13:20 +0100

csiph-web