Re^4: Capture a non-printable char and test what it is

[almsdealer]

Thank you, that link to quote-like characters is very useful. I think one mistake I made was trying to test if the char was the hex value of the escape key using single quotes.

[kcott]

In the time-honoured tradition of TMTOWTDI, if you replace

    if ( $key eq "\e" ) {
        print "Escape pressed\n";
    }

with

    if (
           $key eq "\e"
        && $key eq "\x1b"
        && $key eq "\033"
        && $key eq "\c["
        && $key eq "\x{1b}"
        && $key eq "\o{33}"
        && $key eq "\N{ESCAPE}"
        && $key eq "\N{U+001B}"
        && $key eq v27
        && ord($key) == 27
        && ord($key) == 0x1b
        && ord($key) == 033
        && ord($key) == 0o33
        && ord($key) == 0b11011
    ) {
        print "Escape pressed\n";
    }

you'll get the same result.

I don't claim that's a non-exhaustive list of all possibilities, but I think it's pretty close.

You can find references to all of those in one or more of: perlop; perldata; perlrebackslash.

[afoken]

    if (
           $key eq "\e"
        && $key eq "\x1b"
        && $key eq "\033"
        && $key eq "\c["
        && $key eq "\x{1b}"
        && $key eq "\o{33}"
        && $key eq "\N{ESCAPE}"
        && $key eq "\N{U+001B}"
        && $key eq v27
        && ord($key) == 27
        && ord($key) == 0x1b
        && ord($key) == 033
        && ord($key) == 0o33
        && ord($key) == 0b11011
    ) {
        print "Escape pressed\n";
    }

I wonder how much of it remains after parsing and optimizing:

#!perl

use strict;
use warnings;
use charnames qw( :full );

for my $key ("r", "x", "\e", "z") {
    if (
           $key eq "\e"
        && $key eq "\x1b"
        && $key eq "\033"
        && $key eq "\c["
        && $key eq "\x{1b}"
        && $key eq "\o{33}"
        && $key eq "\N{ESCAPE}"
        && $key eq "\N{U+001B}"
        && $key eq v27
        && ord($key) == 27
        && ord($key) == 0x1b
        && ord($key) == 033
        # that's not perl: && ord($key) == 0o33
        && ord($key) == 0b11011
    ) {
        print "Escape pressed\n";
    }
}

X:\>perl -MO=Deparse 11144112.pl
use charnames (':full');
use warnings;
use strict 'refs';
BEGIN {
    $^H{'charnames_inverse_ords'} = q(HASH(0x2a62c30));
    $^H{'charnames_stringified_inverse_ords'} = q();
    $^H{'charnames'} = q(CODE(0x2b77d90));
    $^H{'charnames_full'} = q(1);
    $^H{'charnames_scripts'} = q();
    $^H{'charnames_name_aliases'} = q(HASH(0x2a62c18));
    $^H{'charnames_ord_aliases'} = q(HASH(0x2a62c90));
    $^H{'charnames_short'} = q(0);
    $^H{'charnames_stringified_names'} = q();
    $^H{'charnames_stringified_ords'} = q();
}
foreach my $key ('r', 'x', "\e", 'z') {
    if ($key eq "\e" and $key eq "\e" and $key eq "\e" and $key eq "\e
+" and $key eq "\e" and $key eq "\e" and $key eq "\e" and $key eq "\e"
+ and $key eq v27 and ord $key == 27 and ord $key == 27 and ord $key =
+= 27 and ord $key == 27) {
        print "Escape pressed\n";
    }
}
11144112.pl syntax OK

X:\>perl -v

This is perl 5, version 14, subversion 2 (v5.14.2) built for MSWin32-x
+64-multi-thread

Copyright 1987-2011, Larry Wall

Perl may be copied only under the terms of either the Artistic License
+ or the
GNU General Public License, which may be found in the Perl 5 source ki
+t.

Complete documentation for Perl, including FAQ lists, should be found 
+on
this system using "man perl" or "perldoc perl".  If you have access to
+ the
Internet, point your browser at http://www.perl.org/, the Perl Home Pa
+ge.

X:\>

So, clearly all variants of writing "\e" and 27 were unified, but I kind of expected that the optimizer would eliminate repeated identical expressions. Like this:

 if ($key eq "\e" and $key eq v27 and ord $key == 27) {
        print "Escape pressed\n";
    }

Alexander

[kcott]

G'day Alexander,

My intention was to show the variety of alternatives available. I would never expect the "... && ... && ..." to be used in a real program.

"# that's not perl: && ord($key) == 0o33"

Actually it is; however, it's very new. See "perl5340delta: New octal syntax 0oddddd".

I have Perl v5.34.0 installed. I checked my code with "perl -e 'use strict; use warnings; ...'" which would normally pick up things introduced since v5.8 (e.g. say). It's good to know that 0o33 passed on my installation without including a "use 5.034;" statement; I'll keep an eye on that in other code. Thanks for spotting this.