ch10.054_best

Perl Best Practices the source code

##############################################################################
##   Code fragment (Recommended) from Chapter 10 of "Perl Best Practices"   ##
##     Copyright (c) O'Reilly & Associates, 2005. All Rights Reserved.      ##
##  See: http://www.oreilly.com/pub/a/oreilly/ask_tim/2001/codepolicy.html  ##
##############################################################################


# Standard modules...
use strict;
use warnings;
use IO::Prompt;
use Carp;
use English qw( -no_match_vars );
use Data::Alias;
use Readonly;


use Scalar::Util qw( openhandle );
 
sub is_interactive {
    # Not interactive if output is not to terminal...
    return 0 if not -t *STDOUT;
 
    # If *ARGV is opened, we're interactive if...
    if (openhandle *ARGV) {
        # ...it's currently opened to the magic '-' file
        return -t *STDIN if $ARGV eq '-';
 
        # ...it's at end-of-file and the next file is the magic '-' file
        return @ARGV>0 && $ARGV[0] eq '-' && -t *STDIN if eof *ARGV;
 
        # ...it's directly attached to the terminal 
        return -t *ARGV;
    }
 
    # If *ARGV isn't opened, it will be interactive if *STDIN is attached 
    # to a terminal and either there are no files specified on the command line
    # or if there are one or more files and the first is the magic '-' file
    return -t *STDIN && (@ARGV==0 || $ARGV[0] eq '-');
}

# and later...

Readonly my $PROMPT => q{> };
 
if (is_interactive()) {
    print $PROMPT;
}