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If I have a program called foo that does something like:

Hello world. Should I continue? (y/n)
[user must type 'y' and hit Enter before continuing]
Thanks!

then how would I write a perl script that launches foo, waits until it
sees the line "Hello world. Should I continue? (y/n)", and
automatically enters the "y" response, all while printing to stdout
the output that foo is printing and the responses that the perl script
is entering? Actually, how can I do it without downloading and
installing any additional perl modules that don't come with the
standard perl distribution? (Even if there is a specialized class
that does it more elegantly, can I just do it with normal reads and
writes?)

I know this must be simple, and I tried to figure it out myself, but I
couldn't find any phrase to Google for that would give me the answer
(e.g. "perl automate entering input", etc.)

Is it just two lines of code? I know asking people to write code for
you is frowned upon, but in this case wouldn't it be faster than
typing a response in English sentences?

Bennett Haselton <> wrote:
>If I have a program called foo that does something like:
>
>Hello world. Should I continue? (y/n)
>[user must type 'y' and hit Enter before continuing]
>Thanks!
>
>then how would I write a perl script that launches foo, waits until it
>sees the line "Hello world. Should I continue? (y/n)", and
>automatically enters the "y" response, all while printing to stdout
>the output that foo is printing and the responses that the perl script
>is entering?

You are looking for the Expect module.

>Actually, how can I do it without downloading and
>installing any additional perl modules that don't come with the
>standard perl distribution?

By re-implementing the code from Expect.pm

> (Even if there is a specialized class
>that does it more elegantly, can I just do it with normal reads and
>writes?)
>
>I know this must be simple, and I tried to figure it out myself, but I
>couldn't find any phrase to Google for that would give me the answer
>(e.g. "perl automate entering input", etc.)
>
>Is it just two lines of code?

Basically you would have to redirect the input and output of the foo
program to be controlled by your program. Only if foo reads/writes
directly from the terminal/to the monitor instead of from/to
stdin/stdout, then it becomes difficult.

jue

On 2010-12-11, Bennett Haselton <> wrote:
> If I have a program called foo that does something like:
>
> Hello world. Should I continue? (y/n)
> [user must type 'y' and hit Enter before continuing]
> Thanks!
>
> then how would I write a perl script that launches foo, waits until it
> sees the line "Hello world. Should I continue? (y/n)", and
> automatically enters the "y" response, all while printing to stdout
> the output that foo is printing and the responses that the perl script
> is entering? Actually, how can I do it without downloading and
> installing any additional perl modules that don't come with the
> standard perl distribution? (Even if there is a specialized class
> that does it more elegantly, can I just do it with normal reads and
> writes?)
>
> I know this must be simple, and I tried to figure it out myself, but I
> couldn't find any phrase to Google for that would give me the answer
> (e.g. "perl automate entering input", etc.)
>
> Is it just two lines of code? I know asking people to write code for
> you is frowned upon, but in this case wouldn't it be faster than
> typing a response in English sentences?


Is there a reason you want to do this with perl? If you are on *nix OS
you may find that you have the expect program already.

Justin.

--
Justin C, by the sea.