Date: Thu, 3 Feb 2005 05:02:28 -0600 From: Jay Moore <jaymo@cromagnon.cullmail.com> To: "Loren M. Lang" <lorenl@alzatex.com> Cc: FreeBSD Mailing List <freebsd-questions@freebsd.org> Subject: Re: running interactive program from shell script Message-ID: <200502030502.28281.jaymo@cromagnon.cullmail.com> In-Reply-To: <20050201122226.GM8619@alzatex.com> References: <200501300533.51350.jaymo@cromagnon.cullmail.com> <20050201122226.GM8619@alzatex.com>
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On Tuesday 01 February 2005 06:22 am, Loren M. Lang wrote: > > I need a shell script that initiates a telnet session to another host. I > > have come up with the following, but unfortunately it terminates when the > > script is finished. What I wanted was for the telnet session to remain > > "alive" and interactive until manually terminated. > > > > Is there a way to accomplish this in a shell script? > > > > I've been told that I'll have to use "expect" or similar to accomplish > > this, but it seems to me that I should be able to do this using just > > Bourne shell commands. > > > > #! /bin/sh > > > > (sleep 3; > > echo "password"; > > sleep 3; > > echo "ls -la"; > > sleep 3; > > ) | telnet -l user 192.168.0.2 > > When any command is run by default, it's standard input comes from the > same place as it's parent process. When you run this shell script from > your prompt, it inherits a standard input coming from your keyboard and > any command it runs inherit the same input as the shell. The same goes > for a processes standard output which it to your screen. Now when you > run a pipe (|), thing are a little different, the standard input and > output get redirected a little bit. The following command sets up a > pipe between two programs: > > leftProgram | rightProgram > > leftProgram's standard input is still from the keyboard, but it's output > gets redirected to the standard input of rightProgram and rightPrograms > standard output goes to the screen as usual. Everything rightProgram > reads on standard input comes only from leftProgram's standard output, > it's no longer reading from the keyboard. When leftProgram's done > sending output and exits, rightProgram sees and End Of File (EOF) and, > in general, will exit since there's nothing more to read. In your > example, you set up a sub-shell which runs 5 command, 3 sleeps and 2 > echos, once the sub-shell exits, telnet just sees and EOF and exits. > The control charater ^D means EOF, on a blank terminal that you don't > mind logging out of, try hitting Control-D and see what happens. It > will logout usually, that's what happened to telnet. I believe you are correct - thanks. Understanding why this is happening has lifted a huge, uncomfortable burden :) But it still seems that there should be a way to do this using a shell script... I will have to think about this some more. Best Rgds, Jay
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