I have a program that I want to be able run in:
  1) interactive mode
  2) non-interactive with input from a commandline option
  3) non-interactive as part of a pipeline

First I parse the commandline args because options can be specified in any of the three cases, and check for case 2. Then I simply test for case 1 by the "-t" operator. 
if (-t STDIN && -t STDOUT) {...} # case 1

[download]
My problem is this: in order to realize case 3 I should know whether there is a pipeline printing to STDIN or not. If so I obvious need a while (<STDIN>) {...} loop. _But_ using this loop without knowing there is a pipeline will cause the program to hang till it gets an EOF on STDIN (which it obviously won't get).

To summarize: How do I know/test/detect there is a pipeline printing to the STDIN of my program so I can use this input?
--
Jaap Karssenberg || Pardus (Larus)? <pardus@cpan.org>
>>>> Zoidberg: So many memories, so many strange fluids gushing out of patients' bodies.... <<<<

In reply to detecting a pipeline on STDIN by Pardus

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.