Re: What is the source of my input, file or STDIN?

From: Drieux (drieux_at_wetware.com)
Date: 01/07/04 

Date: Wed, 7 Jan 2004 10:10:01 -0800
To: Perl Beginners Mailing List <beginners@perl.org>

On Jan 6, 2004, at 1:07 PM, david wrote:
> pgregory@micron.com wrote:
>> Case 3. (this is the difficult case for me) the script is invoked
>> with no file and no pipe to it. I would like the script to
>> end quietly, such as
>>> test.input.source
>>>
>>
>> Instead, it waits for input.
>>
>>> test.input.source
>> no command line args - switching to STDIN
>>
>> and now it waits forever.
>
> select / IO::Select is what you are looking for.
[..]

My compliments to David, as always.

The reason the code is 'waiting for ever' in
the case of having no STDIN is that it is in a
blocking IO Read on STDIN.

So since we have a better spec, I have updated the code
to show how the IO::Select could be used to gate
for the case that the code was called without
command line input, nor a current connection for STDIN.

<http://www.wetware.com/drieux/pbl/perlTrick/CommandLine/
file_or_stdin.plx>

Note all of the noisy 'print statements' are there
merely to show the transition of the logic of the code.

On Jan 6, 2004, at 12:53 PM, Steve Grazzini wrote:

> On Jan 6, 2004, at 3:17 PM, pgregory@micron.com wrote:
>> Case 3. (this is the difficult case for me) the script is
>> invoked with no file and no pipe to it. I would like the
>> script to end quietly
>
> die usage() if @ARGV == 0 and -t;

You might not want to test if there is a
controlling terminal - since that would prevent
the pipe fitting from working unless there was a
controlling terminal. A problem that will crop up
when JoeBob opts wants to use the pipe fitting in
their KSH script...

> I didn't show you how to check for the pipe (-p) because
> this should probably work, too:
>
> % your-script <input.txt

We have Sooooo got to talk about your meds here...

8-)

To be honest, I had not thought about the idea of
'-p' even trying to test to see if it was a pipe
since it is-ish when one connects the pipe fittings
of the standard shell, or as you have done, the
express redirection of input...

[jeeves: 30:] wc -l funk*
       14 funk_env.plx
[jeeves: 31:] ./file* < funk*
no command line args - switching to STDIN
STDIN had 14 number of lines
we saw 14 number of lines
[jeeves: 32:]

The 'redirect in' of "<" simply is a way of changing
how STDIN is feed to the calling program by the shell.
It of course is dependent upon how the shell copes
with re-attaching STDIN|STDOUT combo's...

ciao
drieux 

---

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