=head1 NAME
-perlfaq - frequently asked questions about Perl ($Date: 2005/11/10 00:36:18 $)
+perlfaq - frequently asked questions about Perl ($Date: 2005/12/30 15:04:07 $)
=head1 DESCRIPTION
=head1 Author and Copyright Information
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
other contributors noted in the answers.
All rights reserved.
=head1 NAME
-perlfaq1 - General Questions About Perl ($Revision: 1.18 $, $Date: 2005/04/01 16:15:25 $)
+perlfaq1 - General Questions About Perl ($Revision: 1.19 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq2 - Obtaining and Learning about Perl ($Revision: 1.35 $, $Date: 2005/10/13 19:43:13 $)
+perlfaq2 - Obtaining and Learning about Perl ($Revision: 1.38 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
=item Special Topics
+ Perl Best Practices
+ by Damian Conway
+ ISBN: 0-596-00173-8 [1st edition July 2005]
+ http://www.oreilly.com/catalog/perlbp/
+
+ Higher Order Perl
+ by Mark-Jason Dominus
+ ISBN: 1558607013 [1st edition March 2005]
+ http://hop.perl.plover.com/
+
Perl 6 Now: The Core Ideas Illustrated with Perl 5
by Scott Walters
- ISBN 1-59059-395-2 [1st edition December 2004
+ ISBN 1-59059-395-2 [1st edition December 2004]
http://apress.com/book/bookDisplay.html?bID=355
Mastering Regular Expressions
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq3 - Programming Tools ($Revision: 1.54 $, $Date: 2005/11/17 17:22:02 $)
+perlfaq3 - Programming Tools ($Revision: 1.56 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
my @files;
find(
- sub {
- push @files, $File::Find::name
- if -f $File::Find::name && /\.pm$/
+ sub {
+ push @files, $File::Find::name
+ if -f $File::Find::name && /\.pm$/
},
-
+
@INC
);
You might not need all the power of XS. The Inline::C module lets
you put C code directly in your Perl source. It handles all the
-magic to make it work. You still have to learn at least some of
+magic to make it work. You still have to learn at least some of
the perl API but you won't have to deal with the complexity of the
XS support files.
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq4 - Data Manipulation ($Revision: 1.71 $, $Date: 2005/11/23 07:46:45 $)
+perlfaq4 - Data Manipulation ($Revision: 1.73 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
give you the same time of day, only the day before.
use DateTime;
-
+
my $yesterday = DateTime->now->subtract( days => 1 );
-
+
print "Yesterday was $yesterday\n";
You can also use the C<Date::Calc> module using its Today_and_Now
function.
use Date::Calc qw( Today_and_Now Add_Delta_DHMS );
-
+
my @date_time = Add_Delta_DHMS( Today_and_Now(), -1, 0, 0, 0 );
-
+
print "@date\n";
-
+
Most people try to use the time rather than the calendar to figure out
dates, but that assumes that days are twenty-four hours each. For
most people, there are two days a year when they aren't: the switch to
This is documented in L<perlref>, and although it's not the easiest
thing to read, it does work. In each of these examples, we call the
-function inside the braces of used to dereference a reference. If we
+function inside the braces used to dereference a reference. If we
have a more than one return value, we can construct and dereference an
anonymous array. In this case, we call the function in list context.
- print "The time values are @{ [localtime] }.\n";
+ print "The time values are @{ [localtime] }.\n";
If we want to call the function in scalar context, we have to do a bit
more work. We can really have any code we like inside the braces, so
that is up to you, and you can use code inside the braces.
print "The time is ${\(scalar localtime)}.\n"
-
+
print "The time is ${ my $x = localtime; \$x }.\n";
-
+
If your function already returns a reference, you don't need to create
the reference yourself.
sub timestamp { my $t = localtime; \$t }
-
+
print "The time is ${ timestamp() }.\n";
-
-In most cases, it is probably easier to simply use string
-concatenation, which also forces scalar context.
+
+The C<Interpolation> module can also do a lot of magic for you. You can
+specify a variable name, in this case C<E>, to set up a tied hash that
+does the interpolation for you. It has several other methods to do this
+as well.
+
+ use Interpolation E => 'eval';
+ print "The time values are $E{localtime()}.\n";
+
+In most cases, it is probably easier to simply use string concatenation,
+which also forces scalar context.
print "The time is " . localtime . ".\n";
list context.
my @matches = grep $_ eq $whatever, @array;
-
+
=head2 How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
Use a hash. Here's code to do both and more. It assumes that
create a report which lists the keys in ASCIIbetical order.
my @keys = sort { $a cmp $b } keys %hash;
-
+
foreach my $key ( @keys )
{
printf "%-20s %6d\n", $key, $hash{$value};
}
-We could get more fancy in the C<sort()> block though. Instead of
+We could get more fancy in the C<sort()> block though. Instead of
comparing the keys, we can compute a value with them and use that
-value as the comparison.
+value as the comparison.
For instance, to make our report order case-insensitive, we use
-the C<\L> sequence in a double-quoted string to make everything
+the C<\L> sequence in a double-quoted string to make everything
lowercase. The C<sort()> block then compares the lowercased
values to determine in which order to put the keys.
my @keys = sort { "\L$a" cmp "\L$b" } keys %hash;
-
+
Note: if the computation is expensive or the hash has many elements,
-you may want to look at the Schwartzian Transform to cache the
+you may want to look at the Schwartzian Transform to cache the
computation results.
If we want to sort by the hash value instead, we use the hash key
From there we can get more complex. If the hash values are the same,
we can provide a secondary sort on the hash key.
- my @keys = sort {
- $hash{$a} <=> $hash{$b}
+ my @keys = sort {
+ $hash{$a} <=> $hash{$b}
or
"\L$a" cmp "\L$b"
} keys %hash;
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq5 - Files and Formats ($Revision: 1.40 $, $Date: 2005/11/10 16:06:07 $)
+perlfaq5 - Files and Formats ($Revision: 1.42 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
Unless you have a particular reason to use the two argument form you
should use the three argument form of open() which does not treat any
charcters in the filename as special.
-
+
open FILE, "<", " file "; # filename is " file "
open FILE, ">", ">file"; # filename is ">file"
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq6 - Regular Expressions ($Revision: 1.36 $, $Date: 2005/10/13 19:49:13 $)
+perlfaq6 - Regular Expressions ($Revision: 1.38 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
if (eval { $line =~ /$pattern/ }) { }
-If all you really want to search for a string, not a pattern,
+If all you really want is to search for a string, not a pattern,
then you should either use the index() function, which is made for
-string searching, or if you can't be disabused of using a pattern
+string searching, or, if you can't be disabused of using a pattern
match on a non-pattern, then be sure to use C<\Q>...C<\E>, documented
in L<perlre>.
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq7 - General Perl Language Issues ($Revision: 1.27 $, $Date: 2005/10/28 17:38:32 $)
+perlfaq7 - General Perl Language Issues ($Revision: 1.28 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq8 - System Interaction ($Revision: 1.25 $, $Date: 2005/06/04 04:12:40 $)
+perlfaq8 - System Interaction ($Revision: 1.27 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
=item Keyboard
- Term::Cap Standard perl distribution
- Term::ReadKey CPAN
- Term::ReadLine::Gnu CPAN
- Term::ReadLine::Perl CPAN
- Term::Screen CPAN
+ Term::Cap Standard perl distribution
+ Term::ReadKey CPAN
+ Term::ReadLine::Gnu CPAN
+ Term::ReadLine::Perl CPAN
+ Term::Screen CPAN
=item Screen
- Term::Cap Standard perl distribution
- Curses CPAN
- Term::ANSIColor CPAN
+ Term::Cap Standard perl distribution
+ Curses CPAN
+ Term::ANSIColor CPAN
=item Mouse
- Tk CPAN
+ Tk CPAN
=back
-Some of these specific cases are shown below.
+Some of these specific cases are shown as examples in other answers
+in this section of the perlfaq.
=head2 How do I print something out in color?
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
=head1 NAME
-perlfaq9 - Networking ($Revision: 1.26 $, $Date: 2005/11/21 17:43:13 $)
+perlfaq9 - Networking ($Revision: 1.28 $, $Date: 2005/12/31 00:54:37 $)
=head1 DESCRIPTION
name, or the domain name.
use Net::Domain qw(hostname hostfqdn hostdomain);
-
+
my $host = hostfqdn();
The C<Sys::Hostname> module, included in the standard distribution since
perl5.6, can also get the hostname.
use Sys::Hostname;
-
+
$host = hostname();
To get the IP address, you can use the C<gethostbyname> built-in function
from the <Socket> module, which also comes with perl.
use Socket;
-
- my $address = inet_ntoa(
+
+ my $address = inet_ntoa(
scalar gethostbyname( $host || 'localhost' )
);
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
+Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it
projects / p5sagit/p5-mst-13.2.git / commitdiff