I have a script that does something like that. It deals with text and can read that text from a file if $ARGV[ 0 ] is a readable file, from @ARGV if present but not a file, from a piped command if there's something to read on STDIN or typed in if not. It uses IO::Select to determine if input is waiting to be read on STDIN and thereby makes the assumption that it is being piped to.

use strict;
use warnings;

use IO::Select;

...

my $text;
if ( @ARGV )
{
    if ( -r $ARGV[ 0 ] )
    {
        $text = do {
           local $/;
           <>;
           };
    }
    else
    {
        $text = join q{ }, @ARGV;
    }
}
else
{
    my $select = IO::Select->new();
    $select->add( \ *STDIN );
    print
       qq{Type text, finish with ctrl-D on its own line\n}
       unless $select->can_read( 0.05 );

    $text = do {
       local $/;
       <>;
       };
}

...

# Do something with $text
[download]

I hope this is of use.

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