Utilities for interactive I/O

This module provides three utility subroutines that make it easier to develop interactive applications. The 'ARGV' filehandle, the one that '<>' or an empty 'readline()' uses, has various magic associated with it. It's not actually opened until you try to read from it. Checking '-t ARGV' before you've tried to read from it might give you the wrong answer. Not only that, you might not read from 'ARGV'. If the value in '@ARGV' is the magic filename '-' (a convention to mean the standard filehandle for input or output), 'ARGV' might actually be 'STDIN'. You don't want to think about all of this. This module is discussed in _Perl Best Practices_ on page 218. Also see the 'ARGV' entry in perlvar and the 'readline' entry in perlfunc. * 'is_interactive()' This subroutine returns true if '*ARGV' and the currently selected filehandle (usually '*STDOUT') are connected to the terminal. The test is considerably more sophisticated than: -t *ARGV && -t *STDOUT as it takes into account the magic behaviour of '*ARGV'. You can also pass 'is_interactive' a writable filehandle, in which case it requires that filehandle be connected to a terminal (instead of the currently selected). The usual suspect here is '*STDERR': if ( is_interactive(*STDERR) ) { carp $warning; } * 'interactive()' This subroutine returns '*STDOUT' if 'is_interactive' is true. If 'is_interactive()' is false, 'interactive' returns a filehandle that does not print. This makes it easy to create applications that print out only when the application is interactive: print {interactive} "Please enter a value: "; my $value = <>; You can also pass 'interactive' a writable filehandle, in which case it writes to that filehandle if it is connected to a terminal (instead of writing to '*STDOUT'). Once again, the usual suspect is '*STDERR': print {interactive(*STDERR)} $warning; * 'busy {...}' This subroutine takes a block as its single argument and executes that block. Whilst the block is executed, '*ARGV' is temporarily replaced by a closed filehandle. That is, no input from '*ARGV' is possible in a 'busy' block. Furthermore, any attempts to send input into the 'busy' block through '*ARGV' is intercepted and a warning message is printed to '*STDERR'. The 'busy' call returns a filehandle that contains the intercepted input. A 'busy' block is therefore useful to prevent attempts at input when the program is busy at some non-interactive task.

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