Change 15179 by jhi@alpha on 2002/03/11 21:42:58
FAQ sync.
Affected files ...
.... //depot/perl/pod/perlfaq.pod#28 edit
.... //depot/perl/pod/perlfaq1.pod#40 edit
.... //depot/perl/pod/perlfaq2.pod#51 edit
.... //depot/perl/pod/perlfaq4.pod#68 edit
.... //depot/perl/pod/perlfaq5.pod#40 edit
Differences ...
==== //depot/perl/pod/perlfaq.pod#28 (text) ====
Index: perl/pod/perlfaq.pod
--- perl/pod/perlfaq.pod.~1~ Mon Mar 11 15:00:05 2002
+++ perl/pod/perlfaq.pod Mon Mar 11 15:00:05 2002
@@ -1,6 +1,6 @@
=head1 NAME
-perlfaq - frequently asked questions about Perl ($Date: 2002/01/31 04:27:54 $)
+perlfaq - frequently asked questions about Perl ($Date: 2002/03/11 21:32:23 $)
=head1 DESCRIPTION
@@ -341,6 +341,10 @@
=item *
+How do I get a random number between X and Y?
+
+=item *
+
How do I find the week-of-the-year/day-of-the-year?
=item *
==== //depot/perl/pod/perlfaq1.pod#40 (text) ====
Index: perl/pod/perlfaq1.pod
--- perl/pod/perlfaq1.pod.~1~ Mon Mar 11 15:00:05 2002
+++ perl/pod/perlfaq1.pod Mon Mar 11 15:00:05 2002
@@ -1,6 +1,6 @@
=head1 NAME
-perlfaq1 - General Questions About Perl ($Revision: 1.6 $, $Date: 2002/01/31 01:46:23
$)
+perlfaq1 - General Questions About Perl ($Revision: 1.7 $, $Date: 2002/02/21 14:49:15
+$)
=head1 DESCRIPTION
@@ -216,7 +216,7 @@
can parse Perl." You may or may not choose to follow this usage. For
example, parallelism means "awk and perl" and "Python and Perl" look
OK, while "awk and Perl" and "Python and perl" do not. But never
-write "PERL", because perl isn't really an acronym, apocryphal
+write "PERL", because perl is not an acronym, apocryphal
folklore and post-facto expansions notwithstanding.
=head2 Is it a Perl program or a Perl script?
==== //depot/perl/pod/perlfaq2.pod#51 (text) ====
Index: perl/pod/perlfaq2.pod
--- perl/pod/perlfaq2.pod.~1~ Mon Mar 11 15:00:05 2002
+++ perl/pod/perlfaq2.pod Mon Mar 11 15:00:05 2002
@@ -1,6 +1,6 @@
=head1 NAME
-perlfaq2 - Obtaining and Learning about Perl ($Revision: 1.8 $, $Date: 2002/02/08
22:31:57 $)
+perlfaq2 - Obtaining and Learning about Perl ($Revision: 1.9 $, $Date: 2002/03/09
+21:01:13 $)
=head1 DESCRIPTION
@@ -183,7 +183,7 @@
comp.infosystems.www.authoring.cgi Writing CGI scripts for the Web.
-There is also Usenet gateway to Perl mailing lists sponsored by perl.org at
+There is also a Usenet gateway to Perl mailing lists sponsored by perl.org at
nntp://nntp.perl.org, or a web interface to the same lists at
http://nntp.perl.org/group/. Other groups are listed at
http://lists.perl.org.
==== //depot/perl/pod/perlfaq4.pod#68 (text) ====
Index: perl/pod/perlfaq4.pod
--- perl/pod/perlfaq4.pod.~1~ Mon Mar 11 15:00:05 2002
+++ perl/pod/perlfaq4.pod Mon Mar 11 15:00:05 2002
@@ -1,6 +1,6 @@
=head1 NAME
-perlfaq4 - Data Manipulation ($Revision: 1.14 $, $Date: 2002/02/08 22:30:23 $)
+perlfaq4 - Data Manipulation ($Revision: 1.19 $, $Date: 2002/03/11 22:15:19 $)
=head1 DESCRIPTION
@@ -346,6 +346,20 @@
pseudorandom generator than comes with your operating system, look at
``Numerical Recipes in C'' at http://www.nr.com/ .
+=head2 How do I get a random number between X and Y?
+
+Use the following simple function. It selects a random integer between
+(and possibly including!) the two given integers, e.g.,
+C<random_int_in(50,120)>
+
+ sub random_int_in ($$) {
+ my($min, $max) = @_;
+ # Assumes that the two arguments are integers themselves!
+ return $min if $min == $max;
+ ($min, $max) = ($max, $min) if $min > $max;
+ return $min + int rand(1 + $max - $min);
+ }
+
=head1 Data: Dates
=head2 How do I find the week-of-the-year/day-of-the-year?
@@ -690,6 +704,11 @@
while ($string =~ /-\d+/g) { $count++ }
print "There are $count negative numbers in the string";
+Another version uses a global match in list context, then assigns the
+result to a scalar, producing a count of the number of matches.
+
+ $count = () = $string =~ /-\d+/g;
+
=head2 How do I capitalize all the words on one line?
To make the first letter of each word upper case:
@@ -1125,11 +1144,11 @@
That being said, there are several ways to approach this. If you
are going to make this query many times over arbitrary string values,
-the fastest way is probably to invert the original array and keep an
-associative array lying about whose keys are the first array's values.
+the fastest way is probably to invert the original array and maintain a
+hash whose keys are the first array's values.
@blues = qw/azure cerulean teal turquoise lapis-lazuli/;
- undef %is_blue;
+ %is_blue = ();
for (@blues) { $is_blue{$_} = 1 }
Now you can check whether $is_blue{$some_color}. It might have been a
@@ -1139,7 +1158,7 @@
array. This kind of an array will take up less space:
@primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31);
- undef @is_tiny_prime;
+ @is_tiny_prime = ();
for (@primes) { $is_tiny_prime[$_] = 1 }
# or simply @istiny_prime[@primes] = (1) x @primes;
@@ -1885,9 +1904,9 @@
if (/^-?\d+$/) { print "is an integer\n" }
if (/^[+-]?\d+$/) { print "is a +/- integer\n" }
if (/^-?\d+\.?\d*$/) { print "is a real number\n" }
- if (/^-?(?:\d+(?:\.\d*)?|\.\d+)$/) { print "is a decimal number" }
+ if (/^-?(?:\d+(?:\.\d*)?|\.\d+)$/) { print "is a decimal number\n" }
if (/^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/)
- { print "a C float" }
+ { print "a C float\n" }
If you're on a POSIX system, Perl's supports the C<POSIX::strtod>
function. Its semantics are somewhat cumbersome, so here's a C<getnum>
==== //depot/perl/pod/perlfaq5.pod#40 (text) ====
Index: perl/pod/perlfaq5.pod
--- perl/pod/perlfaq5.pod.~1~ Mon Mar 11 15:00:05 2002
+++ perl/pod/perlfaq5.pod Mon Mar 11 15:00:05 2002
@@ -1,6 +1,6 @@
=head1 NAME
-perlfaq5 - Files and Formats ($Revision: 1.9 $, $Date: 2002/02/11 19:30:21 $)
+perlfaq5 - Files and Formats ($Revision: 1.12 $, $Date: 2002/03/11 22:25:25 $)
=head1 DESCRIPTION
@@ -350,38 +350,24 @@
=head2 How can I output my numbers with commas added?
-This one will do it for you:
+This one from Benjamin Goldberg will do it for you:
- sub commify {
- my $number = shift;
- 1 while ($number =~ s/^([-+]?\d+)(\d{3})/$1,$2/);
- return $number;
- }
+ s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g;
- $n = 23659019423.2331;
- print "GOT: ", commify($n), "\n";
+or written verbosely:
- GOT: 23,659,019,423.2331
-
-You can't just:
-
- s/^([-+]?\d+)(\d{3})/$1,$2/g;
+ s/(
+ ^[-+]? # beginning of number.
+ \d{1,3}? # first digits before first comma
+ (?= # followed by, (but not included in the match) :
+ (?>(?:\d{3})+) # some positive multiple of three digits.
+ (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever.
+ )
+ | # or:
+ \G\d{3} # after the last group, get three digits
+ (?=\d) # but they have to have more digits after them.
+ )/$1,/xg;
-because you have to put the comma in and then recalculate your
-position.
-
-Alternatively, this code commifies all numbers in a line regardless of
-whether they have decimal portions, are preceded by + or -, or
-whatever:
-
- # from Andrew Johnson <[EMAIL PROTECTED]>
- sub commify {
- my $input = shift;
- $input = reverse $input;
- $input =~ s<(\d\d\d)(?=\d)(?!\d*\.)><$1,>g;
- return scalar reverse $input;
- }
-
=head2 How can I translate tildes (~) in a filename?
Use the <> (glob()) operator, documented in L<perlfunc>. Older
@@ -501,35 +487,24 @@
Normally perl ignores trailing blanks in filenames, and interprets
certain leading characters (or a trailing "|") to mean something
-special. To avoid this, you might want to use a routine like the one below.
-It turns incomplete pathnames into explicit relative ones, and tacks a
-trailing null byte on the name to make perl leave it alone:
+special.
- sub safe_filename {
- local $_ = shift;
- s#^([^./])#./$1#;
- $_ .= "\0";
- return $_;
- }
+The three argument form of open() lets you specify the mode
+separately from the filename. The open() function treats
+special mode characters and whitespace in the filename as
+literals
- $badpath = "<<<something really wicked ";
- $fn = safe_filename($badpath");
- open(FH, "> $fn") or "couldn't open $badpath: $!";
+ open FILE, "<", " file "; # filename is " file "
+ open FILE, ">", ">file"; # filename is ">file"
+
-This assumes that you are using POSIX (portable operating systems
-interface) paths. If you are on a closed, non-portable, proprietary
-system, you may have to adjust the C<"./"> above.
-
-It would be a lot clearer to use sysopen(), though:
+It may be a lot clearer to use sysopen(), though:
use Fcntl;
$badpath = "<<<something really wicked ";
sysopen (FH, $badpath, O_WRONLY | O_CREAT | O_TRUNC)
or die "can't open $badpath: $!";
-For more information, see also the new L<perlopentut> if you have it
-(new for 5.6).
-
=head2 How can I reliably rename a file?
If your operating system supports a proper mv(1) utility or its functional
@@ -688,14 +663,17 @@
=head2 How do I get a file's timestamp in perl?
-If you want to retrieve the time at which the file was last read,
-written, or had its meta-data (owner, etc) changed, you use the B<-M>,
-B<-A>, or B<-C> file test operations as documented in L<perlfunc>. These
-retrieve the age of the file (measured against the start-time of your
-program) in days as a floating point number. To retrieve the "raw"
-time in seconds since the epoch, you would call the stat function,
-then use localtime(), gmtime(), or POSIX::strftime() to convert this
-into human-readable form.
+If you want to retrieve the time at which the file was last
+read, written, or had its meta-data (owner, etc) changed,
+you use the B<-M>, B<-A>, or B<-C> file test operations as
+documented in L<perlfunc>. These retrieve the age of the
+file (measured against the start-time of your program) in
+days as a floating point number. Some platforms may not have
+all of these times. See L<perlport> for details. To
+retrieve the "raw" time in seconds since the epoch, you
+would call the stat function, then use localtime(),
+gmtime(), or POSIX::strftime() to convert this into
+human-readable form.
Here's an example:
End of Patch.
