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15.12. Managing the Screen
15.12.1. Problem
You want to control the screen layout
or highlighting, detect when special keys are pressed, or present
full-screen menus, but you don't want to think about what kind of
display device the user
has.
15.12.2. Solution
Use the Curses
module from CPAN, which makes use of your native
curses(3) library.
15.12.3. Description
The curses library provides easy access to the
full-screen display in an efficient and device-independent fashion.
(By display, we mean any cursor-addressable monitor.) With Curses,
you write high-level code to put data on the logical display,
building it up character by character or string by string. When you
want output to show up, call the refresh function.
The library generates output consisting only of the changes on the
virtual display since the last call to refresh.
This is particularly appreciated on a slow connection.The example program in Example 15-5, called
rep, demonstrates this. Call it with arguments
of the program to run, like any of these:% rep ps aux
% rep netstat
% rep -2.5 lpq
The rep script will repeatedly call the listed
command, printing its output to the screen, updating only what
changed since the previous run. This is most effective when the
changes between runs are small. It maintains the current date in
reverse video at the bottom-right corner of your screen.By default, rep waits 10 seconds before
rerunning the command. You can change this delay period by calling it
an optional number of seconds (which can be a decimal number) as
shown in the previous example when calling lpq.
You may also hit any key during the pause for it to run the command
right then.
Example 15-5. rep
#!/usr/bin/perl -w
# rep - screen repeat command
use strict;
use Curses;
my $timeout = 10;
if (@ARGV && $ARGV[0] =~ /^-(\d+\.?\d*)$/) {
$timeout = $1;
shift;
}
die "usage: $0 [ -timeout ] cmd args\n" unless @ARGV;
initscr( ); # start screen
noecho( );
cbreak( );
nodelay(1); # so getch( ) is non-blocking
$SIG{INT} = sub { done("Ouch!") };
sub done { endwin( ); print "@_\n"; exit; }
while (1) {
while ((my $key = getch( )) ne ERR) { # maybe multiple keys
done("See ya") if $key eq 'q'
}
my @data = `(@ARGV) 2>&1`; # gather output+errors
for (my $i = 0; $i < $LINES; $i++) {
addstr($i, 0, $data[$i] || ' ' x $COLS);
}
standout( );
addstr($LINES-1, $COLS - 24, scalar localtime);
standend( );
move(0,0);
refresh( ); # flush new output to display
my ($in, $out) = ('', '');
vec($in,fileno(STDIN),1) = 1; # look for key on stdin
select($out = $in,undef,undef,$timeout);# wait up to this long
}
Curses lets you tell whether the user typed one of the arrow keys or
those other funny keys, like HOME or
INSERT. This is normally difficult, because those
keys send multiple bytes. With Curses, it's easy:keypad(1); # enable keypad mode
$key = getch( );
if ($key eq 'k' || # vi mode
$key eq "\cP" || # emacs mode
$key eq KEY_UP) # arrow mode
{
# do something
}
Other Curses functions let you read the text at particular screen
coordinates, control highlighting and standout mode, and even manage
multiple windows.The perlmenu
module, also from CPAN, is built on top of the lower-level Curses
module. It provides high-level access to menus and fill-out forms.
Here's a sample form from the perlmenu distribution:Template Entry Demonstration
Address Data Example Record # ___
Name: [__ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __]
Addr: [__ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __]
City: [__ __ __ __ __ __ __ __ __] State: [__] Zip: [\\\\\]
Phone: (\\\) \\\-\\\\ Password: [^^^^^^^^]
Enter all information available.
Edit fields with left/right arrow keys or "delete".
Switch fields with "Tab" or up/down arrow keys.
Indicate completion by pressing "Return".
Refresh screen with "Control-L".
Abort this demo here with "Control-X".
The user types in the areas indicated, with regular text indicated by
underline fields, numeric data by backslashed fields, and starred-out
data with circumflexed fields. This is reminiscent of Perl's formats,
except that forms are used for output, not input.
15.12.4. See Also
Your system's curses(3) manpage (if you have
it); the documentation for the Curses and the perlmenu modules from
CPAN; Chapter 7 of Programming Perl, or
perlform(1); Recipe 3.10
|  | |
| 15.11. Editing Input |  | 15.13. Controlling Another Program with Expect |
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