[%# DO NOT EDIT THIS FILE: generated from perlfaq (https://github.com/perl-doc-cats/perlfaq) -%] [%- # Used to get info from htmlify to ttree page.import({ title => "perlfaq4", section => "faq", description => "Perl Frequently Asked Questions, Perl FAQ", keywords => "perl, perl faq, perlfaq" }); perlfaq_version = 5.021011; -%]
perlfaq4 - Data Manipulation
version 5.021011
This section of the FAQ answers questions related to manipulating numbers, dates, strings, arrays, hashes, and miscellaneous data issues.
For the long explanation, see David Goldberg's "What Every Computer Scientist Should Know About Floating-Point Arithmetic" (http://web.cse.msu.edu/~cse320/Documents/FloatingPoint.pdf).
Internally, your computer represents floating-point numbers in binary. Digital (as in powers of two) computers cannot store all numbers exactly. Some real numbers lose precision in the process. This is a problem with how computers store numbers and affects all computer languages, not just Perl.
perlnumber shows the gory details of number representations and conversions.
To limit the number of decimal places in your numbers, you can use the printf
or sprintf
function. See "Floating-point Arithmetic" in perlop for more details.
printf "%.2f", 10/3; my $number = sprintf "%.2f", 10/3;
Your int()
is most probably working just fine. It's the numbers that aren't quite what you think.
First, see the answer to "Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?".
For example, this
print int(0.6/0.2-2), "\n";
will in most computers print 0, not 1, because even such simple numbers as 0.6 and 0.2 cannot be presented exactly by floating-point numbers. What you think in the above as 'three' is really more like 2.9999999999999995559.
(contributed by brian d foy)
You're probably trying to convert a string to a number, which Perl only converts as a decimal number. When Perl converts a string to a number, it ignores leading spaces and zeroes, then assumes the rest of the digits are in base 10:
my $string = '0644'; print $string + 0; # prints 644 print $string + 44; # prints 688, certainly not octal!
This problem usually involves one of the Perl built-ins that has the same name a Unix command that uses octal numbers as arguments on the command line. In this example, chmod
on the command line knows that its first argument is octal because that's what it does:
%prompt> chmod 644 file
If you want to use the same literal digits (644) in Perl, you have to tell Perl to treat them as octal numbers either by prefixing the digits with a 0
or using oct
:
chmod( 0644, $filename ); # right, has leading zero chmod( oct(644), $filename ); # also correct
The problem comes in when you take your numbers from something that Perl thinks is a string, such as a command line argument in @ARGV
:
chmod( $ARGV[0], $filename ); # wrong, even if "0644" chmod( oct($ARGV[0]), $filename ); # correct, treat string as octal
You can always check the value you're using by printing it in octal notation to ensure it matches what you think it should be. Print it in octal and decimal format:
printf "0%o %d", $number, $number;
Remember that int()
merely truncates toward 0. For rounding to a certain number of digits, sprintf()
or printf()
is usually the easiest route.
printf("%.3f", 3.1415926535); # prints 3.142
The POSIX module (part of the standard Perl distribution) implements ceil()
, floor()
, and a number of other mathematical and trigonometric functions.
use POSIX; my $ceil = ceil(3.5); # 4 my $floor = floor(3.5); # 3
In 5.000 to 5.003 perls, trigonometry was done in the Math::Complex module. With 5.004, the Math::Trig module (part of the standard Perl distribution) implements the trigonometric functions. Internally it uses the Math::Complex module and some functions can break out from the real axis into the complex plane, for example the inverse sine of 2.
Rounding in financial applications can have serious implications, and the rounding method used should be specified precisely. In these cases, it probably pays not to trust whichever system of rounding is being used by Perl, but instead to implement the rounding function you need yourself.
To see why, notice how you'll still have an issue on half-way-point alternation:
for (my $i = 0; $i < 1.01; $i += 0.05) { printf "%.1f ",$i} 0.0 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.8 0.8 0.9 0.9 1.0 1.0
Don't blame Perl. It's the same as in C. IEEE says we have to do this. Perl numbers whose absolute values are integers under 2**31 (on 32-bit machines) will work pretty much like mathematical integers. Other numbers are not guaranteed.
As always with Perl there is more than one way to do it. Below are a few examples of approaches to making common conversions between number representations. This is intended to be representational rather than exhaustive.
Some of the examples later in perlfaq4 use the Bit::Vector module from CPAN. The reason you might choose Bit::Vector over the perl built-in functions is that it works with numbers of ANY size, that it is optimized for speed on some operations, and for at least some programmers the notation might be familiar.
Using perl's built in conversion of 0x
notation:
my $dec = 0xDEADBEEF;
Using the hex
function:
my $dec = hex("DEADBEEF");
Using pack
:
my $dec = unpack("N", pack("H8", substr("0" x 8 . "DEADBEEF", -8)));
Using the CPAN module Bit::Vector
:
use Bit::Vector; my $vec = Bit::Vector->new_Hex(32, "DEADBEEF"); my $dec = $vec->to_Dec();
Using sprintf
:
my $hex = sprintf("%X",<PHONE_NUMBER>); # upper case A-F my $hex = sprintf("%x",<PHONE_NUMBER>); # lower case a-f
Using unpack
:
my $hex = unpack("H*", pack("N",<PHONE_NUMBER>));
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(32, -559038737); my $hex = $vec->to_Hex();
And Bit::Vector supports odd bit counts:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(33,<PHONE_NUMBER>); $vec->Resize(32); # suppress leading 0 if unwanted my $hex = $vec->to_Hex();
Using Perl's built in conversion of numbers with leading zeros:
my $dec =<PHONE_NUMBER>57; # note the leading 0!
Using the oct
function:
my $dec = oct("33653337357");
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new(32); $vec->Chunk_List_Store(3, split(//, reverse "33653337357")); my $dec = $vec->to_Dec();
Using sprintf
:
my $oct = sprintf("%o",<PHONE_NUMBER>);
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(32, -559038737); my $oct = reverse join('', $vec->Chunk_List_Read(3));
Perl 5.6 lets you write binary numbers directly with the 0b
notation:
my $number = 0b10110110;
Using oct
:
my $input = "10110110"; my $decimal = oct( "0b$input" );
Using pack
and ord
:
my $decimal = ord(pack('B8', '10110110'));
Using pack
and unpack
for larger strings:
my $int = unpack("N", pack("B32", substr("0" x 32 . "11110101011011011111011101111", -32))); my $dec = sprintf("%d", $int); # substr() is used to left-pad a 32-character string with zeros.
Using Bit::Vector:
my $vec = Bit::Vector->new_Bin(32, "11011110101011011011111011101111"); my $dec = $vec->to_Dec();
Using sprintf
(perl 5.6+):
my $bin = sprintf("%b",<PHONE_NUMBER>);
Using unpack
:
my $bin = unpack("B*", pack("N",<PHONE_NUMBER>));
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(32, -559038737); my $bin = $vec->to_Bin();
The remaining transformations (e.g. hex -> oct, bin -> hex, etc.) are left as an exercise to the inclined reader.
The behavior of binary arithmetic operators depends on whether they're used on numbers or strings. The operators treat a string as a series of bits and work with that (the string "3"
is the bit pattern 00110011
). The operators work with the binary form of a number (the number 3
is treated as the bit pattern 00000011
).
So, saying 11 & 3
performs the "and" operation on numbers (yielding 3
). Saying "11" & "3"
performs the "and" operation on strings (yielding "1"
).
Most problems with &
and |
arise because the programmer thinks they have a number but really it's a string or vice versa. To avoid this, stringify the arguments explicitly (using ""
or qq()
) or convert them to numbers explicitly (using 0+$arg
). The rest arise because the programmer says:
if ("\020\020" & "\101\101") { # ... }
but a string consisting of two null bytes (the result of "\020\020" & "\101\101"
) is not a false value in Perl. You need:
if ( ("\020\020" & "\101\101") !~ /[^\000]/) { # ... }
Use the Math::Matrix or Math::MatrixReal modules (available from CPAN) or the PDL extension (also available from CPAN).
To call a function on each element in an array, and collect the results, use:
my @results = map { my_func($_) } @array;
For example:
my @triple = map { 3 * $_ } @single;
To call a function on each element of an array, but ignore the results:
foreach my $iterator (@array) { some_func($iterator); }
To call a function on each integer in a (small) range, you can use:
my @results = map { some_func($_) } (5 .. 25);
but you should be aware that in this form, the ..
operator creates a list of all integers in the range, which can take a lot of memory for large ranges. However, the problem does not occur when using ..
within a for
loop, because in that case the range operator is optimized to iterate over the range, without creating the entire list. So
my @results = (); for my $i (5 .. 500_005) { push(@results, some_func($i)); }
or even
push(@results, some_func($_)) for 5 .. 500_005;
will not create an intermediate list of 500,000 integers.
Get the http://www.cpan.org/modules/by-module/Roman module.
If you're using a version of Perl before 5.004, you must call srand
once at the start of your program to seed the random number generator.
BEGIN { srand() if $] < 5.004 }
5.004 and later automatically call srand
at the beginning. Don't call srand
more than once--you make your numbers less random, rather than more.
Computers are good at being predictable and bad at being random (despite appearances caused by bugs in your programs :-). The random article in the "Far More Than You Ever Wanted To Know" collection in http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz, courtesy of Tom Phoenix, talks more about this. John von Neumann said, "Anyone who attempts to generate random numbers by deterministic means is, of course, living in a state of sin."
Perl relies on the underlying system for the implementation of rand
and srand
; on some systems, the generated numbers are not random enough (especially on Windows : see http://www.perlmonks.org/?node_id=803632). Several CPAN modules in the Math
namespace implement better pseudorandom generators; see for example Math::Random::MT ("Mersenne Twister", fast), or Math::TrulyRandom (uses the imperfections in the system's timer to generate random numbers, which is rather slow). More algorithms for random numbers are described in "Numerical Recipes in C" at http://www.nr.com/
To get a random number between two values, you can use the rand()
built-in to get a random number between 0 and 1. From there, you shift that into the range that you want.
rand($x)
returns a number such that 0 <= rand($x) < $x
. Thus what you want to have perl figure out is a random number in the range from 0 to the difference between your X and Y.
That is, to get a number between 10 and 15, inclusive, you want a random number between 0 and 5 that you can then add to 10.
my $number = 10 + int rand( 15-10+1 ); # ( 10,11,12,13,14, or 15 )
Hence you derive the following simple function to abstract that. It selects a random integer between the two given integers (inclusive). For example: random_int_between(50,120)
.
sub random_int_between { my($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); }
The day of the year is in the list returned by the localtime
function. Without an argument localtime
uses the current time.
my $day_of_year = (localtime)[7];
The POSIX module can also format a date as the day of the year or week of the year.
use POSIX qw/strftime/; my $day_of_year = strftime "%j", localtime; my $week_of_year = strftime "%W", localtime;
To get the day of year for any date, use POSIX's mktime
to get a time in epoch seconds for the argument to localtime
.
use POSIX qw/mktime strftime/; my $week_of_year = strftime "%W", localtime( mktime( 0, 0, 0, 18, 11, 87 ) );
You can also use Time::Piece, which comes with Perl and provides a localtime
that returns an object:
use Time::Piece; my $day_of_year = localtime->yday; my $week_of_year = localtime->week;
The Date::Calc module provides two functions to calculate these, too:
use Date::Calc; my $day_of_year = Day_of_Year( 1987, 12, 18 ); my $week_of_year = Week_of_Year( 1987, 12, 18 );
Use the following simple functions:
sub get_century { return int((((localtime(shift || time))[5] + 1999))/100); } sub get_millennium { return 1+int((((localtime(shift || time))[5] + 1899))/1000); }
On some systems, the POSIX module's strftime()
function has been extended in a non-standard way to use a %C
format, which they sometimes claim is the "century". It isn't, because on most such systems, this is only the first two digits of the four-digit year, and thus cannot be used to determine reliably the current century or millennium.
(contributed by brian d foy)
You could just store all your dates as a number and then subtract. Life isn't always that simple though.
The Time::Piece module, which comes with Perl, replaces localtime with a version that returns an object. It also overloads the comparison operators so you can compare them directly:
use Time::Piece; my $date1 = localtime( $some_time ); my $date2 = localtime( $some_other_time ); if( $date1 < $date2 ) { print "The date was in the past\n"; }
You can also get differences with a subtraction, which returns a Time::Seconds object:
my $date_diff = $date1 - $date2; print "The difference is ", $date_diff->days, " days\n";
If you want to work with formatted dates, the Date::Manip, Date::Calc, or DateTime modules can help you.
If it's a regular enough string that it always has the same format, you can split it up and pass the parts to timelocal
in the standard Time::Local module. Otherwise, you should look into the Date::Calc, Date::Parse, and Date::Manip modules from CPAN.
(contributed by brian d foy and Dave Cross)
You can use the Time::Piece module, part of the Standard Library, which can convert a date/time to a Julian Day:
$ perl -MTime::Piece -le 'print localtime->julian_day' 2455607.7959375
Or the modified Julian Day:
$ perl -MTime::Piece -le 'print localtime->mjd' 55607.2961226851
Or even the day of the year (which is what some people think of as a Julian day):
$ perl -MTime::Piece -le 'print localtime->yday' 45
You can also do the same things with the DateTime module:
$ perl -MDateTime -le'print DateTime->today->jd' 2453401.5 $ perl -MDateTime -le'print DateTime->today->mjd' 53401 $ perl -MDateTime -le'print DateTime->today->doy' 31
You can use the Time::JulianDay module available on CPAN. Ensure that you really want to find a Julian day, though, as many people have different ideas about Julian days (see http://www.hermetic.ch/cal_stud/jdn.htm for instance):
$ perl -MTime::JulianDay -le 'print local_julian_day( time )' 55608
(contributed by brian d foy)
To do it correctly, you can use one of the Date
modules since they work with calendars instead of times. The DateTime module makes it simple, and give you the same time of day, only the day before, despite daylight saving time changes:
use DateTime; my $yesterday = DateTime->now->subtract( days => 1 ); print "Yesterday was $yesterday\n";
You can also use the 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_time\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 and from summer time throws this off. For example, the rest of the suggestions will be wrong sometimes:
Starting with Perl 5.10, Time::Piece and Time::Seconds are part of the standard distribution, so you might think that you could do something like this:
use Time::Piece; use Time::Seconds; my $yesterday = localtime() - ONE_DAY; # WRONG print "Yesterday was $yesterday\n";
The Time::Piece module exports a new localtime
that returns an object, and Time::Seconds exports the ONE_DAY
constant that is a set number of seconds. This means that it always gives the time 24 hours ago, which is not always yesterday. This can cause problems around the end of daylight saving time when there's one day that is 25 hours long.
You have the same problem with Time::Local, which will give the wrong answer for those same special cases:
# contributed by Gunnar Hjalmarsson use Time::Local; my $today = timelocal 0, 0, 12, ( localtime )[3..5]; my ($d, $m, $y) = ( localtime $today-86400 )[3..5]; # WRONG printf "Yesterday: %d-%02d-%02d\n", $y+1900, $m+1, $d;
(contributed by brian d foy)
Perl itself never had a Y2K problem, although that never stopped people from creating Y2K problems on their own. See the documentation for localtime
for its proper use.
Starting with Perl 5.12, localtime
and gmtime
can handle dates past 03:14:08 January 19, 2038, when a 32-bit based time would overflow. You still might get a warning on a 32-bit perl
:
% perl5.12 -E 'say scalar localtime( 0x9FFF_FFFFFFFF )' Integer overflow in hexadecimal number at -e line 1. Wed Nov 1 19:42:39 5576711
On a 64-bit perl
, you can get even larger dates for those really long running projects:
% perl5.12 -E 'say scalar gmtime( 0x9FFF_FFFFFFFF )' Thu Nov 2 00:42:39 5576711
You're still out of luck if you need to keep track of decaying protons though.
(contributed by brian d foy)
There are many ways to ensure that values are what you expect or want to accept. Besides the specific examples that we cover in the perlfaq, you can also look at the modules with "Assert" and "Validate" in their names, along with other modules such as Regexp::Common.
Some modules have validation for particular types of input, such as Business::ISBN, Business::CreditCard, Email::Valid, and Data::Validate::IP.
It depends just what you mean by "escape". URL escapes are dealt with in perlfaq9. Shell escapes with the backslash (\
) character are removed with
s/\\(.)/$1/g;
This won't expand "\n"
or "\t"
or any other special escapes.
(contributed by brian d foy)
You can use the substitution operator to find pairs of characters (or runs of characters) and replace them with a single instance. In this substitution, we find a character in (.)
. The memory parentheses store the matched character in the back-reference \g1
and we use that to require that the same thing immediately follow it. We replace that part of the string with the character in $1
.
s/(.)\g1/$1/g;
We can also use the transliteration operator, tr///
. In this example, the search list side of our tr///
contains nothing, but the c
option complements that so it contains everything. The replacement list also contains nothing, so the transliteration is almost a no-op since it won't do any replacements (or more exactly, replace the character with itself). However, the s
option squashes duplicated and consecutive characters in the string so a character does not show up next to itself
my $str = 'Haarlem'; # in the Netherlands $str =~ tr///cs; # Now Harlem, like in New York
(contributed by brian d foy)
This is documented in 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 used to dereference a reference. If we have 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";
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 we simply have to end with the scalar reference, although how you do that is up to you, and you can use code inside the braces. Note that the use of parens creates a list context, so we need scalar
to force the scalar context on the function:
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";
The Interpolation
module can also do a lot of magic for you. You can specify a variable name, in this case 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";
To find something between two single characters, a pattern like /x([^x]*)x/
will get the intervening bits in $1. For multiple ones, then something more like /alpha(.*?)omega/
would be needed. For nested patterns and/or balanced expressions, see the so-called (?PARNO) construct (available since perl 5.10). The CPAN module Regexp::Common can help to build such regular expressions (see in particular Regexp::Common::balanced and Regexp::Common::delimited).
More complex cases will require to write a parser, probably using a parsing module from CPAN, like Regexp::Grammars, Parse::RecDescent, Parse::Yapp, Text::Balanced, or Marpa::R2.
Use reverse()
in scalar context, as documented in "reverse" in perlfunc.
my $reversed = reverse $string;
You can do it yourself:
1 while $string =~ s/\t+/' ' x (length($&) * 8 - length($`) % 8)/e;
Or you can just use the Text::Tabs module (part of the standard Perl distribution).
use Text::Tabs; my @expanded_lines = expand(@lines_with_tabs);
Use Text::Wrap (part of the standard Perl distribution):
use Text::Wrap; print wrap("\t", ' ', @paragraphs);
The paragraphs you give to Text::Wrap should not contain embedded newlines. Text::Wrap doesn't justify the lines (flush-right).
Or use the CPAN module Text::Autoformat. Formatting files can be easily done by making a shell alias, like so:
alias fmt="perl -i -MText::Autoformat -n0777 \ -e 'print autoformat $_, {all=>1}' $*"
See the documentation for Text::Autoformat to appreciate its many capabilities.
You can access the first characters of a string with substr(). To get the first character, for example, start at position 0 and grab the string of length 1.
my $string = "Just another Perl Hacker"; my $first_char = substr( $string, 0, 1 ); # 'J'
To change part of a string, you can use the optional fourth argument which is the replacement string.
substr( $string, 13, 4, "Perl 5.8.0" );
You can also use substr() as an lvalue.
substr( $string, 13, 4 ) = "Perl 5.8.0";
You have to keep track of N yourself. For example, let's say you want to change the fifth occurrence of "whoever"
or "whomever"
into "whosoever"
or "whomsoever"
, case insensitively. These all assume that $_ contains the string to be altered.
$count = 0; s{((whom?)ever)}{ ++$count == 5 # is it the 5th? ? "${2}soever" # yes, swap : $1 # renege and leave it there }ige;
In the more general case, you can use the /g
modifier in a while
loop, keeping count of matches.
$WANT = 3; $count = 0; $_ = "One fish two fish red fish blue fish"; while (/(\w+)\s+fish\b/gi) { if (++$count == $WANT) { print "The third fish is a $1 one.\n"; } }
That prints out: "The third fish is a red one."
You can also use a repetition count and repeated pattern like this:
/(?:\w+\s+fish\s+){2}(\w+)\s+fish/i;
There are a number of ways, with varying efficiency. If you want a count of a certain single character (X) within a string, you can use the tr///
function like so:
my $string = "ThisXlineXhasXsomeXx'sXinXit"; my $count = ($string =~ tr/X//); print "There are $count X characters in the string";
This is fine if you are just looking for a single character. However, if you are trying to count multiple character substrings within a larger string, tr///
won't work. What you can do is wrap a while() loop around a global pattern match. For example, let's count negative integers:
my $string = "-9 55 48 -2 23 -76 4 14 -44"; my $count = 0; while ($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.
my $count = () = $string =~ /-\d+/g;
(contributed by brian d foy)
Damian Conway's Text::Autoformat handles all of the thinking for you.
use Text::Autoformat; my $x = "Dr. Strangelove or: How I Learned to Stop ". "Worrying and Love the Bomb"; print $x, "\n"; for my $style (qw( sentence title highlight )) { print autoformat($x, { case => $style }), "\n"; }
How do you want to capitalize those words?
FRED AND BARNEY'S LODGE # all uppercase Fred And Barney's Lodge # title case Fred and Barney's Lodge # highlight case
It's not as easy a problem as it looks. How many words do you think are in there? Wait for it... wait for it.... If you answered 5 you're right. Perl words are groups of \w+
, but that's not what you want to capitalize. How is Perl supposed to know not to capitalize that s
after the apostrophe? You could try a regular expression:
$string =~ s/ ( (^\w) #at the beginning of the line | # or (\s\w) #preceded by whitespace ) /\U$1/xg; $string =~ s/([\w']+)/\u\L$1/g;
Now, what if you don't want to capitalize that "and"? Just use Text::Autoformat and get on with the next problem. :)
Several modules can handle this sort of parsing--Text::Balanced, Text::CSV, Text::CSV_XS, and Text::ParseWords, among others.
Take the example case of trying to split a string that is comma-separated into its different fields. You can't use split(/,/)
because you shouldn't split if the comma is inside quotes. For example, take a data line like this:
SAR001,"","Cimetrix, Inc","Bob Smith","CAM",N,8,1,0,7,"Error, Core Dumped"
Due to the restriction of the quotes, this is a fairly complex problem. Thankfully, we have Jeffrey Friedl, author of Mastering Regular Expressions, to handle these for us. He suggests (assuming your string is contained in $text
):
my @new = (); push(@new, $+) while $text =~ m{ "([^\"\\]*(?:\\.[^\"\\]*)*)",? # groups the phrase inside the quotes | ([^,]+),? | , }gx; push(@new, undef) if substr($text,-1,1) eq ',';
If you want to represent quotation marks inside a quotation-mark-delimited field, escape them with backslashes (eg, "like \"this\""
.
Alternatively, the Text::ParseWords module (part of the standard Perl distribution) lets you say:
use Text::ParseWords; @new = quotewords(",", 0, $text);
For parsing or generating CSV, though, using Text::CSV rather than implementing it yourself is highly recommended; you'll save yourself odd bugs popping up later by just using code which has already been tried and tested in production for years.
(contributed by brian d foy)
A substitution can do this for you. For a single line, you want to replace all the leading or trailing whitespace with nothing. You can do that with a pair of substitutions:
s/^\s+//; s/\s+$//;
You can also write that as a single substitution, although it turns out the combined statement is slower than the separate ones. That might not matter to you, though:
s/^\s+|\s+$//g;
In this regular expression, the alternation matches either at the beginning or the end of the string since the anchors have a lower precedence than the alternation. With the /g
flag, the substitution makes all possible matches, so it gets both. Remember, the trailing newline matches the \s+
, and the $
anchor can match to the absolute end of the string, so the newline disappears too. Just add the newline to the output, which has the added benefit of preserving "blank" (consisting entirely of whitespace) lines which the ^\s+
would remove all by itself:
while( <> ) { s/^\s+|\s+$//g; print "$_\n"; }
For a multi-line string, you can apply the regular expression to each logical line in the string by adding the /m
flag (for "multi-line"). With the /m
flag, the $
matches before an embedded newline, so it doesn't remove it. This pattern still removes the newline at the end of the string:
$string =~ s/^\s+|\s+$//gm;
Remember that lines consisting entirely of whitespace will disappear, since the first part of the alternation can match the entire string and replace it with nothing. If you need to keep embedded blank lines, you have to do a little more work. Instead of matching any whitespace (since that includes a newline), just match the other whitespace:
$string =~ s/^[\t\f ]+|[\t\f ]+$//mg;
In the following examples, $pad_len
is the length to which you wish to pad the string, $text
or $num
contains the string to be padded, and $pad_char
contains the padding character. You can use a single character string constant instead of the $pad_char
variable if you know what it is in advance. And in the same way you can use an integer in place of $pad_len
if you know the pad length in advance.
The simplest method uses the sprintf
function. It can pad on the left or right with blanks and on the left with zeroes and it will not truncate the result. The pack
function can only pad strings on the right with blanks and it will truncate the result to a maximum length of $pad_len
.
# Left padding a string with blanks (no truncation): my $padded = sprintf("%${pad_len}s", $text); my $padded = sprintf("%*s", $pad_len, $text); # same thing # Right padding a string with blanks (no truncation): my $padded = sprintf("%-${pad_len}s", $text); my $padded = sprintf("%-*s", $pad_len, $text); # same thing # Left padding a number with 0 (no truncation): my $padded = sprintf("%0${pad_len}d", $num); my $padded = sprintf("%0*d", $pad_len, $num); # same thing # Right padding a string with blanks using pack (will truncate): my $padded = pack("A$pad_len",$text);
If you need to pad with a character other than blank or zero you can use one of the following methods. They all generate a pad string with the x
operator and combine that with $text
. These methods do not truncate $text
.
Left and right padding with any character, creating a new string:
my $padded = $pad_char x ( $pad_len - length( $text ) ) . $text; my $padded = $text . $pad_char x ( $pad_len - length( $text ) );
Left and right padding with any character, modifying $text
directly:
substr( $text, 0, 0 ) = $pad_char x ( $pad_len - length( $text ) ); $text .= $pad_char x ( $pad_len - length( $text ) );
(contributed by brian d foy)
If you know the columns that contain the data, you can use substr
to extract a single column.
my $column = substr( $line, $start_column, $length );
You can use split
if the columns are separated by whitespace or some other delimiter, as long as whitespace or the delimiter cannot appear as part of the data.
my $line = ' fred barney betty '; my @columns = split /\s+/, $line; # ( '', 'fred', 'barney', 'betty' ); my $line = 'fred||barney||betty'; my @columns = split /\|/, $line; # ( 'fred', '', 'barney', '', 'betty' );
If you want to work with comma-separated values, don't do this since that format is a bit more complicated. Use one of the modules that handle that format, such as Text::CSV, Text::CSV_XS, or Text::CSV_PP.
If you want to break apart an entire line of fixed columns, you can use unpack
with the A (ASCII) format. By using a number after the format specifier, you can denote the column width. See the pack
and unpack
entries in perlfunc for more details.
my @fields = unpack( $line, "A8 A8 A8 A16 A4" );
Note that spaces in the format argument to unpack
do not denote literal spaces. If you have space separated data, you may want split
instead.
(contributed by brian d foy)
You can use the Text::Soundex
module. If you want to do fuzzy or close matching, you might also try the String::Approx, and Text::Metaphone, and Text::DoubleMetaphone modules.
(contributed by brian d foy)
If you can avoid it, don't, or if you can use a templating system, such as Text::Template or Template Toolkit, do that instead. You might even be able to get the job done with sprintf
or printf
:
my $string = sprintf 'Say hello to %s and %s', $foo, $bar;
However, for the one-off simple case where I don't want to pull out a full templating system, I'll use a string that has two Perl scalar variables in it. In this example, I want to expand $foo
and $bar
to their variable's values:
my $foo = 'Fred'; my $bar = 'Barney'; $string = 'Say hello to $foo and $bar';
One way I can do this involves the substitution operator and a double /e
flag. The first /e
evaluates $1
on the replacement side and turns it into $foo
. The second /e starts with $foo
and replaces it with its value. $foo
, then, turns into 'Fred', and that's finally what's left in the string:
$string =~ s/(\$\w+)/$1/eeg; # 'Say hello to Fred and Barney'
The /e
will also silently ignore violations of strict, replacing undefined variable names with the empty string. Since I'm using the /e
flag (twice even!), I have all of the same security problems I have with eval
in its string form. If there's something odd in $foo
, perhaps something like @{[ system "rm -rf /" ]}
, then I could get myself in trouble.
To get around the security problem, I could also pull the values from a hash instead of evaluating variable names. Using a single /e
, I can check the hash to ensure the value exists, and if it doesn't, I can replace the missing value with a marker, in this case ???
to signal that I missed something:
my $string = 'This has $foo and $bar'; my %Replacements = ( foo => 'Fred', ); # $string =~ s/\$(\w+)/$Replacements{$1}/g; $string =~ s/\$(\w+)/ exists $Replacements{$1} ? $Replacements{$1} : '???' /eg; print $string;
The problem is that those double-quotes force stringification--coercing numbers and references into strings--even when you don't want them to be strings. Think of it this way: double-quote expansion is used to produce new strings. If you already have a string, why do you need more?
If you get used to writing odd things like these:
print "$var"; # BAD my $new = "$old"; # BAD somefunc("$var"); # BAD
You'll be in trouble. Those should (in 99.8% of the cases) be the simpler and more direct:
print $var; my $new = $old; somefunc($var);
Otherwise, besides slowing you down, you're going to break code when the thing in the scalar is actually neither a string nor a number, but a reference:
func(\@array); sub func { my $aref = shift; my $oref = "$aref"; # WRONG }
You can also get into subtle problems on those few operations in Perl that actually do care about the difference between a string and a number, such as the magical ++
autoincrement operator or the syscall() function.
Stringification also destroys arrays.
my @lines = `command`; print "@lines"; # WRONG - extra blanks print @lines; # right
Here documents are found in perlop. Check for these three things:
If you want to indent the text in the here document, you can do this:
# all in one (my $VAR = <<HERE_TARGET) =~ s/^\s+//gm; your text goes here HERE_TARGET
But the HERE_TARGET must still be flush against the margin. If you want that indented also, you'll have to quote in the indentation.
(my $quote = <<' FINIS') =~ s/^\s+//gm; ...we will have peace, when you and all your works have perished--and the works of your dark master to whom you would deliver us.  --Theoden in /usr/src/perl/taint.c FINIS $quote =~ s/\s+--/\n--/;
A nice general-purpose fixer-upper function for indented here documents follows. It expects to be called with a here document as its argument. It looks to see whether each line begins with a common substring, and if so, strips that substring off. Otherwise, it takes the amount of leading whitespace found on the first line and removes that much off each subsequent line.
sub fix { local $_ = shift; my ($white, $leader); # common whitespace and common leading string if (/^\s*(?:([^\w\s]+)(\s*).*\n)(?:\s*\g1\g2?.*\n)+$/) { ($white, $leader) = ($2, quotemeta($1)); } else { ($white, $leader) = (/^(\s+)/, ''); } s/^\s*?$leader(?:$white)?//gm; return $_; }
This works with leading special strings, dynamically determined:
my $remember_the_main = fix<<' MAIN_INTERPRETER_LOOP'; @@@ int @@@ runops() { @@@ SAVEI32(runlevel); @@@ runlevel++; @@@ while ( op = (*op->op_ppaddr)() ); @@@ TAINT_NOT; @@@ return 0; @@@ } MAIN_INTERPRETER_LOOP
Or with a fixed amount of leading whitespace, with remaining indentation correctly preserved:
my $poem = fix<<EVER_ON_AND_ON; Now far ahead the Road has gone, And I must follow, if I can, Pursuing it with eager feet, Until it joins some larger way Where many paths and errands meet. And whither then? I cannot say. --Bilbo in /usr/src/perl/pp_ctl.c EVER_ON_AND_ON
(contributed by brian d foy)
A list is a fixed collection of scalars. An array is a variable that holds a variable collection of scalars. An array can supply its collection for list operations, so list operations also work on arrays:
# slices ( 'dog', 'cat', 'bird' )[2,3]; @animals[2,3]; # iteration foreach ( qw( dog cat bird ) ) { ... } foreach ( @animals ) { ... } my @three = grep { length == 3 } qw( dog cat bird ); my @three = grep { length == 3 } @animals; # supply an argument list wash_animals( qw( dog cat bird ) ); wash_animals( @animals );
Array operations, which change the scalars, rearrange them, or add or subtract some scalars, only work on arrays. These can't work on a list, which is fixed. Array operations include shift
, unshift
, push
, pop
, and splice
.
An array can also change its length:
$#animals = 1; # truncate to two elements $#animals = 10000; # pre-extend to 10,001 elements
You can change an array element, but you can't change a list element:
$animals[0] = 'Rottweiler'; qw( dog cat bird )[0] = 'Rottweiler'; # syntax error! foreach ( @animals ) { s/^d/fr/; # works fine } foreach ( qw( dog cat bird ) ) { s/^d/fr/; # Error! Modification of read only value! }
However, if the list element is itself a variable, it appears that you can change a list element. However, the list element is the variable, not the data. You're not changing the list element, but something the list element refers to. The list element itself doesn't change: it's still the same variable.
You also have to be careful about context. You can assign an array to a scalar to get the number of elements in the array. This only works for arrays, though:
my $count = @animals; # only works with arrays
If you try to do the same thing with what you think is a list, you get a quite different result.  The comma operator (yes, it's an operator!) in scalar context evaluates its lefthand side, throws away the result, and evaluates it's righthand side and returns the result. In effect, that list-lookalike assigns to $scalar
it's rightmost value. Many people mess this up because they choose a list-lookalike whose last element is also the count they expect:
my $scalar = ( 1, 2, 3 ); # $scalar gets 3, accidentally
(contributed by brian d foy)
The difference is the sigil, that special character in front of the array name. The $
sigil means "exactly one item", while the @
sigil means "zero or more items".
The confusion arises because people incorrectly assume that the sigil denotes the variable type.
The $array[1]
is a single-element access to the array. It's going to return the item in index 1 (or undef if there is no item there). If you intend to get exactly one element from the array, this is the form you should use.
The @array[1]
is an array slice, although it has only one index. You can pull out multiple elements simultaneously by specifying additional indices as a list, like @array[1,4,3,0]
.
Using a slice on the lefthand side of the assignment supplies list context to the righthand side. This can lead to unexpected results. For instance, if you want to read a single line from a filehandle, assigning to a scalar value is fine:
$array[1] = <STDIN>;
However, in list context, the line input operator returns all of the lines as a list. The first line goes into @array[1]
and the rest of the lines mysteriously disappear:
@array[1] = <STDIN>; # most likely not what you want
Either the use warnings
pragma or the -w flag will warn you when you use an array slice with a single index.
(contributed by brian d foy)
Use a hash. When you think the words "unique" or "duplicated", think "hash keys".
If you don't care about the order of the elements, you could just create the hash then extract the keys. It's not important how you create that hash: just that you use keys
to get the unique elements.
my %hash = map { $_, 1 } @array; # or a hash slice: @hash{ @array } = (); # or a foreach: $hash{$_} = 1 foreach ( @array ); my @unique = keys %hash;
If you want to use a module, try the uniq
function from List::MoreUtils. In list context it returns the unique elements, preserving their order in the list. In scalar context, it returns the number of unique elements.
use List::MoreUtils qw(uniq); my @unique = uniq( 1, 2, 3, 4, 4, 5, 6, 5, 7 ); # 1,2,3,4,5,6,7 my $unique = uniq( 1, 2, 3, 4, 4, 5, 6, 5, 7 ); # 7
You can also go through each element and skip the ones you've seen before. Use a hash to keep track. The first time the loop sees an element, that element has no key in %Seen
. The next
statement creates the key and immediately uses its value, which is undef
, so the loop continues to the push
and increments the value for that key. The next time the loop sees that same element, its key exists in the hash and the value for that key is true (since it's not 0 or undef
), so the next skips that iteration and the loop goes to the next element.
my @unique = (); my %seen = (); foreach my $elem ( @array ) { next if $seen{ $elem }++; push @unique, $elem; }
You can write this more briefly using a grep, which does the same thing.
my %seen = (); my @unique = grep { ! $seen{ $_ }++ } @array;
(portions of this answer contributed by Anno Siegel and brian d foy)
Hearing the word "in" is an indication that you probably should have used a hash, not a list or array, to store your data. Hashes are designed to answer this question quickly and efficiently. Arrays aren't.
That being said, there are several ways to approach this. In Perl 5.10 and later, you can use the smart match operator to check that an item is contained in an array or a hash:
use 5.010; if( $item ~~ @array ) { say "The array contains $item" } if( $item ~~ %hash ) { say "The hash contains $item" }
With earlier versions of Perl, you have to do a bit more work. 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 maintain a hash whose keys are the first array's values:
my @blues = qw/azure cerulean teal turquoise lapis-lazuli/; my %is_blue = (); for (@blues) { $is_blue{$_} = 1 }
Now you can check whether $is_blue{$some_color}
. It might have been a good idea to keep the blues all in a hash in the first place.
If the values are all small integers, you could use a simple indexed array. This kind of an array will take up less space:
my @primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31); my @is_tiny_prime = (); for (@primes) { $is_tiny_prime[$_] = 1 } # or simply @istiny_prime[@primes] = (1) x @primes;
Now you check whether $is_tiny_prime[$some_number].
If the values in question are integers instead of strings, you can save quite a lot of space by using bit strings instead:
my @articles = ( 1..10, 150..2000, 2017 ); undef $read; for (@articles) { vec($read,$_,1) = 1 }
Now check whether vec($read,$n,1)
is true for some $n
.
These methods guarantee fast individual tests but require a re-organization of the original list or array. They only pay off if you have to test multiple values against the same array.
If you are testing only once, the standard module List::Util exports the function first
for this purpose. It works by stopping once it finds the element. It's written in C for speed, and its Perl equivalent looks like this subroutine:
sub first (&@) { my $code = shift; foreach (@_) { return $_ if &{$code}(); } undef; }
If speed is of little concern, the common idiom uses grep in scalar context (which returns the number of items that passed its condition) to traverse the entire list. This does have the benefit of telling you how many matches it found, though.
my $is_there = grep $_ eq $whatever, @array;
If you want to actually extract the matching elements, simply use grep in list context.
my @matches = grep $_ eq $whatever, @array;
Use a hash. Here's code to do both and more. It assumes that each element is unique in a given array:
my (@union, @intersection, @difference); my %count = (); foreach my $element (@array1, @array2) { $count{$element}++ } foreach my $element (keys %count) { push @union, $element; push @{ $count{$element} > 1 ? \@intersection : \@difference }, $element; }
Note that this is the symmetric difference, that is, all elements in either A or in B but not in both. Think of it as an xor operation.
With Perl 5.10 and later, the smart match operator can give you the answer with the least amount of work:
use 5.010; if( @array1 ~~ @array2 ) { say "The arrays are the same"; } if( %hash1 ~~ %hash2 ) # doesn't check values! { say "The hash keys are the same"; }
The following code works for single-level arrays. It uses a stringwise comparison, and does not distinguish defined versus undefined empty strings. Modify if you have other needs.
$are_equal = compare_arrays(\@frogs, \@toads); sub compare_arrays { my ($first, $second) = @_; no warnings; # silence spurious -w undef complaints return 0 unless @$first == @$second; for (my $i = 0; $i < @$first; $i++) { return 0 if $first->[$i] ne $second->[$i]; } return 1; }
For multilevel structures, you may wish to use an approach more like this one. It uses the CPAN module FreezeThaw:
use FreezeThaw qw(cmpStr); my @a = my @b = ( "this", "that", [ "more", "stuff" ] ); printf "a and b contain %s arrays\n", cmpStr(\@a, \@b) == 0 ? "the same" : "different";
This approach also works for comparing hashes. Here we'll demonstrate two different answers:
use FreezeThaw qw(cmpStr cmpStrHard); my %a = my %b = ( "this" => "that", "extra" => [ "more", "stuff" ] ); $a{EXTRA} = \%b; $b{EXTRA} = \%a; printf "a and b contain %s hashes\n", cmpStr(\%a, \%b) == 0 ? "the same" : "different"; printf "a and b contain %s hashes\n", cmpStrHard(\%a, \%b) == 0 ? "the same" : "different";
The first reports that both those the hashes contain the same data, while the second reports that they do not. Which you prefer is left as an exercise to the reader.
To find the first array element which satisfies a condition, you can use the first()
function in the List::Util module, which comes with Perl 5.8. This example finds the first element that contains "Perl".
use List::Util qw(first); my $element = first { /Perl/ } @array;
If you cannot use List::Util, you can make your own loop to do the same thing. Once you find the element, you stop the loop with last.
my $found; foreach ( @array ) { if( /Perl/ ) { $found = $_; last } }
If you want the array index, use the firstidx()
function from List::MoreUtils
:
use List::MoreUtils qw(firstidx); my $index = firstidx { /Perl/ } @array;
Or write it yourself, iterating through the indices and checking the array element at each index until you find one that satisfies the condition:
my( $found, $index ) = ( undef, -1 ); for( $i = 0; $i < @array; $i++ ) { if( $array[$i] =~ /Perl/ ) { $found = $array[$i]; $index = $i; last; } }
(contributed by brian d foy)
Perl's arrays do not have a fixed size, so you don't need linked lists if you just want to add or remove items. You can use array operations such as push
, pop
, shift
, unshift
, or splice
to do that.
Sometimes, however, linked lists can be useful in situations where you want to "shard" an array so you have many small arrays instead of a single big array. You can keep arrays longer than Perl's largest array index, lock smaller arrays separately in threaded programs, reallocate less memory, or quickly insert elements in the middle of the chain.
Steve Lembark goes through the details in his YAPC::NA 2009 talk "Perly Linked Lists" ( http://www.slideshare.net/lembark/perly-linked-lists ), although you can just use his LinkedList::Single module.
(contributed by brian d foy)
If you want to cycle through an array endlessly, you can increment the index modulo the number of elements in the array:
my @array = qw( a b c ); my $i = 0; while( 1 ) { print $array[ $i++ % @array ], "\n"; last if $i > 20; }
You can also use Tie::Cycle to use a scalar that always has the next element of the circular array:
use Tie::Cycle; tie my $cycle, 'Tie::Cycle', [ qw( FFFFFF 000000 FFFF00 ) ]; print $cycle; # FFFFFF print $cycle; # 000000 print $cycle; # FFFF00
The Array::Iterator::Circular creates an iterator object for circular arrays:
use Array::Iterator::Circular; my $color_iterator = Array::Iterator::Circular->new( qw(red green blue orange) ); foreach ( 1 .. 20 ) { print $color_iterator->next, "\n"; }
If you either have Perl 5.8.0 or later installed, or if you have Scalar-List-Utils 1.03 or later installed, you can say:
use List::Util 'shuffle'; @shuffled = shuffle(@list);
If not, you can use a Fisher-Yates shuffle.
sub fisher_yates_shuffle { my $deck = shift; # $deck is a reference to an array return unless @$deck; # must not be empty! my $i = @$deck; while (--$i) { my $j = int rand ($i+1); @$deck[$i,$j] = @$deck[$j,$i]; } } # shuffle my mpeg collection # my @mpeg = <audio/*/*.mp3>; fisher_yates_shuffle( \@mpeg ); # randomize @mpeg in place print @mpeg;
Note that the above implementation shuffles an array in place, unlike the List::Util::shuffle()
which takes a list and returns a new shuffled list.
You've probably seen shuffling algorithms that work using splice, randomly picking another element to swap the current element with
srand; @new = (); @old = 1 .. 10; # just a demo while (@old) { push(@new, splice(@old, rand @old, 1)); }
This is bad because splice is already O(N), and since you do it N times, you just invented a quadratic algorithm; that is, O(N**2). This does not scale, although Perl is so efficient that you probably won't notice this until you have rather largish arrays.
Use for
/foreach
:
for (@lines) { s/foo/bar/; # change that word tr/XZ/ZX/; # swap those letters }
Here's another; let's compute spherical volumes:
my @volumes = @radii; for (@volumes) { # @volumes has changed parts $_ **= 3; $_ *= (4/3) * 3.14159; # this will be constant folded }
which can also be done with map()
which is made to transform one list into another:
my @volumes = map {$_ ** 3 * (4/3) * 3.14159} @radii;
If you want to do the same thing to modify the values of the hash, you can use the values
function. As of Perl 5.6 the values are not copied, so if you modify $orbit (in this case), you modify the value.
for my $orbit ( values %orbits ) { ($orbit **= 3) *= (4/3) * 3.14159; }
Prior to perl 5.6 values
returned copies of the values, so older perl code often contains constructions such as @orbits{keys %orbits}
instead of values %orbits
where the hash is to be modified.
Use the rand()
function (see "rand" in perlfunc):
my $index = rand @array; my $element = $array[$index];
Or, simply:
my $element = $array[ rand @array ];
Use the List::Permutor module on CPAN. If the list is actually an array, try the Algorithm::Permute module (also on CPAN). It's written in XS code and is very efficient:
use Algorithm::Permute; my @array = 'a'..'d'; my $p_iterator = Algorithm::Permute->new ( \@array ); while (my @perm = $p_iterator->next) { print "next permutation: (@perm)\n"; }
For even faster execution, you could do:
use Algorithm::Permute; my @array = 'a'..'d'; Algorithm::Permute::permute { print "next permutation: (@array)\n"; } @array;
Here's a little program that generates all permutations of all the words on each line of input. The algorithm embodied in the permute()
function is discussed in Volume 4 (still unpublished) of Knuth's The Art of Computer Programming and will work on any list:
#!/usr/bin/perl -n # Fischer-Krause ordered permutation generator sub permute (&@) { my $code = shift; my @idx = 0..$#_; while ( $code->(@_[@idx]) ) { my $p = $#idx; --$p while $idx[$p-1] > $idx[$p]; my $q = $p or return; push @idx, reverse splice @idx, $p; ++$q while $idx[$p-1] > $idx[$q]; @idx[$p-1,$q]=@idx[$q,$p-1]; } } permute { print "@_\n" } split;
The Algorithm::Loops module also provides the NextPermute
and NextPermuteNum
functions which efficiently find all unique permutations of an array, even if it contains duplicate values, modifying it in-place: if its elements are in reverse-sorted order then the array is reversed, making it sorted, and it returns false; otherwise the next permutation is returned.
NextPermute
uses string order and NextPermuteNum
numeric order, so you can enumerate all the permutations of 0..9
like this:
use Algorithm::Loops qw(NextPermuteNum); my @list= 0..9; do { print "@list\n" } while NextPermuteNum @list;
Supply a comparison function to sort() (described in "sort" in perlfunc):
@list = sort { $a <=> $b } @list;
The default sort function is cmp, string comparison, which would sort (1, 2, 10)
into (1, 10, 2)
. <=>
, used above, is the numerical comparison operator.
If you have a complicated function needed to pull out the part you want to sort on, then don't do it inside the sort function. Pull it out first, because the sort BLOCK can be called many times for the same element. Here's an example of how to pull out the first word after the first number on each item, and then sort those words case-insensitively.
my @idx; for (@data) { my $item; ($item) = /\d+\s*(\S+)/; push @idx, uc($item); } my @sorted = @data[ sort { $idx[$a] cmp $idx[$b] } 0 .. $#idx ];
which could also be written this way, using a trick that's come to be known as the Schwartzian Transform:
my @sorted = map { $_->[0] } sort { $a->[1] cmp $b->[1] } map { [ $_, uc( (/\d+\s*(\S+)/)[0]) ] } @data;
If you need to sort on several fields, the following paradigm is useful.
my @sorted = sort { field1($a) <=> field1($b) || field2($a) cmp field2($b) || field3($a) cmp field3($b) } @data;
This can be conveniently combined with precalculation of keys as given above.
See the sort article in the "Far More Than You Ever Wanted To Know" collection in http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz for more about this approach.
See also the question later in perlfaq4 on sorting hashes.
Use pack()
and unpack()
, or else vec()
and the bitwise operations.
For example, you don't have to store individual bits in an array (which would mean that you're wasting a lot of space). To convert an array of bits to a string, use vec()
to set the right bits. This sets $vec
to have bit N set only if $ints[N]
was set:
my @ints = (...); # array of bits, e.g. ( 1, 0, 0, 1, 1, 0 ... ) my $vec = ''; foreach( 0 .. $#ints ) { vec($vec,$_,1) = 1 if $ints[$_]; }
The string $vec
only takes up as many bits as it needs. For instance, if you had 16 entries in @ints
, $vec
only needs two bytes to store them (not counting the scalar variable overhead).
Here's how, given a vector in $vec
, you can get those bits into your @ints
array:
sub bitvec_to_list { my $vec = shift; my @ints; # Find null-byte density then select best algorithm if ($vec =~ tr/\0// / length $vec > 0.95) { use integer; my $i; # This method is faster with mostly null-bytes while($vec =~ /[^\0]/g ) { $i = -9 + 8 * pos $vec; push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); } } else { # This method is a fast general algorithm use integer; my $bits = unpack "b*", $vec; push @ints, 0 if $bits =~ s/^(\d)// && $1; push @ints, pos $bits while($bits =~ /1/g); } return \@ints; }
This method gets faster the more sparse the bit vector is. (Courtesy of Tim Bunce and Winfried Koenig.)
You can make the while loop a lot shorter with this suggestion from Benjamin Goldberg:
while($vec =~ /[^\0]+/g ) { push @ints, grep vec($vec, $_, 1), $-[0] * 8 .. $+[0] * 8; }
Or use the CPAN module Bit::Vector:
my $vector = Bit::Vector->new($num_of_bits); $vector->Index_List_Store(@ints); my @ints = $vector->Index_List_Read();
Bit::Vector provides efficient methods for bit vector, sets of small integers and "big int" math.
Here's a more extensive illustration using vec():
# vec demo my $vector = "\xff\x0f\xef\xfe"; print "Ilya's string \\xff\\x0f\\xef\\xfe represents the number ", unpack("N", $vector), "\n"; my $is_set = vec($vector, 23, 1); print "Its 23rd bit is ", $is_set ? "set" : "clear", ".\n"; pvec($vector); set_vec(1,1,1); set_vec(3,1,1); set_vec(23,1,1); set_vec(3,1,3); set_vec(3,2,3); set_vec(3,4,3); set_vec(3,4,7); set_vec(3,8,3); set_vec(3,8,7); set_vec(0,32,17); set_vec(1,32,17); sub set_vec { my ($offset, $width, $value) = @_; my $vector = ''; vec($vector, $offset, $width) = $value; print "offset=$offset width=$width value=$value\n"; pvec($vector); } sub pvec { my $vector = shift; my $bits = unpack("b*", $vector); my $i = 0; my $BASE = 8; print "vector length in bytes: ", length($vector), "\n"; @bytes = unpack("A8" x length($vector), $bits); print "bits are: @bytes\n\n"; }
The short story is that you should probably only use defined on scalars or functions, not on aggregates (arrays and hashes). See "defined" in perlfunc in the 5.004 release or later of Perl for more detail.
(contributed by brian d foy)
There are a couple of ways that you can process an entire hash. You can get a list of keys, then go through each key, or grab a one key-value pair at a time.
To go through all of the keys, use the keys
function. This extracts all of the keys of the hash and gives them back to you as a list. You can then get the value through the particular key you're processing:
foreach my $key ( keys %hash ) { my $value = $hash{$key} ... }
Once you have the list of keys, you can process that list before you process the hash elements. For instance, you can sort the keys so you can process them in lexical order:
foreach my $key ( sort keys %hash ) { my $value = $hash{$key} ... }
Or, you might want to only process some of the items. If you only want to deal with the keys that start with text:
, you can select just those using grep
:
foreach my $key ( grep /^text:/, keys %hash ) { my $value = $hash{$key} ... }
If the hash is very large, you might not want to create a long list of keys. To save some memory, you can grab one key-value pair at a time using each()
, which returns a pair you haven't seen yet:
while( my( $key, $value ) = each( %hash ) ) { ... }
The each
operator returns the pairs in apparently random order, so if ordering matters to you, you'll have to stick with the keys
method.
The each()
operator can be a bit tricky though. You can't add or delete keys of the hash while you're using it without possibly skipping or re-processing some pairs after Perl internally rehashes all of the elements. Additionally, a hash has only one iterator, so if you mix keys
, values
, or each
on the same hash, you risk resetting the iterator and messing up your processing. See the each
entry in perlfunc for more details.
(contributed by brian d foy)
Before you decide to merge two hashes, you have to decide what to do if both hashes contain keys that are the same and if you want to leave the original hashes as they were.
If you want to preserve the original hashes, copy one hash (%hash1
) to a new hash (%new_hash
), then add the keys from the other hash (%hash2
to the new hash. Checking that the key already exists in %new_hash
gives you a chance to decide what to do with the duplicates:
my %new_hash = %hash1; # make a copy; leave %hash1 alone foreach my $key2 ( keys %hash2 ) { if( exists $new_hash{$key2} ) { warn "Key [$key2] is in both hashes!"; # handle the duplicate (perhaps only warning) ... next; } else { $new_hash{$key2} = $hash2{$key2}; } }
If you don't want to create a new hash, you can still use this looping technique; just change the %new_hash
to %hash1
.
foreach my $key2 ( keys %hash2 ) { if( exists $hash1{$key2} ) { warn "Key [$key2] is in both hashes!"; # handle the duplicate (perhaps only warning) ... next; } else { $hash1{$key2} = $hash2{$key2}; } }
If you don't care that one hash overwrites keys and values from the other, you could just use a hash slice to add one hash to another. In this case, values from %hash2
replace values from %hash1
when they have keys in common:
@hash1{ keys %hash2 } = values %hash2;
(contributed by brian d foy)
The easy answer is "Don't do that!"
If you iterate through the hash with each(), you can delete the key most recently returned without worrying about it. If you delete or add other keys, the iterator may skip or double up on them since perl may rearrange the hash table. See the entry for each()
in perlfunc.
Create a reverse hash:
my %by_value = reverse %by_key; my $key = $by_value{$value};
That's not particularly efficient. It would be more space-efficient to use:
while (my ($key, $value) = each %by_key) { $by_value{$value} = $key; }
If your hash could have repeated values, the methods above will only find one of the associated keys. This may or may not worry you. If it does worry you, you can always reverse the hash into a hash of arrays instead:
while (my ($key, $value) = each %by_key) { push @{$key_list_by_value{$value}}, $key; }
(contributed by brian d foy)
This is very similar to "How do I process an entire hash?", also in perlfaq4, but a bit simpler in the common cases.
You can use the keys()
built-in function in scalar context to find out have many entries you have in a hash:
my $key_count = keys %hash; # must be scalar context!
If you want to find out how many entries have a defined value, that's a bit different. You have to check each value. A grep
is handy:
my $defined_value_count = grep { defined } values %hash;
You can use that same structure to count the entries any way that you like. If you want the count of the keys with vowels in them, you just test for that instead:
my $vowel_count = grep { /[aeiou]/ } keys %hash;
The grep
in scalar context returns the count. If you want the list of matching items, just use it in list context instead:
my @defined_values = grep { defined } values %hash;
The keys()
function also resets the iterator, which means that you may see strange results if you use this between uses of other hash operators such as each()
.
(contributed by brian d foy)
To sort a hash, start with the keys. In this example, we give the list of keys to the sort function which then compares them ASCIIbetically (which might be affected by your locale settings). The output list has the keys in ASCIIbetical order. Once we have the keys, we can go through them to 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, $hash{$key}; }
We could get more fancy in the sort()
block though. Instead of comparing the keys, we can compute a value with them and use that value as the comparison.
For instance, to make our report order case-insensitive, we use lc
to lowercase the keys before comparing them:
my @keys = sort { lc $a cmp lc $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 computation results.
If we want to sort by the hash value instead, we use the hash key to look it up. We still get out a list of keys, but this time they are ordered by their value.
my @keys = sort { $hash{$a} <=> $hash{$b} } keys %hash;
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} or "\L$a" cmp "\L$b" } keys %hash;
You can look into using the DB_File
module and tie()
using the $DB_BTREE
hash bindings as documented in "In Memory Databases" in DB_File. The Tie::IxHash module from CPAN might also be instructive.  Are you sure you need to do this? :)
Hashes contain pairs of scalars: the first is the key, the second is the value. The key will be coerced to a string, although the value can be any kind of scalar: string, number, or reference. If a key $key
is present in %hash, exists($hash{$key})
will return true. The value for a given key can be undef
, in which case $hash{$key}
will be undef
while exists $hash{$key}
will return true. This corresponds to ($key
, undef
) being in the hash.
Pictures help... Here's the %hash
table:
keys values +------+------+ | a | 3 | | x | 7 | | d | 0 | | e | 2 | +------+------+
And these conditions hold
$hash{'a'} is true $hash{'d'} is false defined $hash{'d'} is true defined $hash{'a'} is true exists $hash{'a'} is true (Perl 5 only) grep ($_ eq 'a', keys %hash) is true
If you now say
undef $hash{'a'}
your table now reads:
keys values +------+------+ | a | undef| | x | 7 | | d | 0 | | e | 2 | +------+------+
and these conditions now hold; changes in caps:
$hash{'a'} is FALSE $hash{'d'} is false defined $hash{'d'} is true defined $hash{'a'} is FALSE exists $hash{'a'} is true (Perl 5 only) grep ($_ eq 'a', keys %hash) is true
Notice the last two: you have an undef value, but a defined key!
Now, consider this:
delete $hash{'a'}
your table now reads:
keys values +------+------+ | x | 7 | | d | 0 | | e | 2 | +------+------+
and these conditions now hold; changes in caps:
$hash{'a'} is false $hash{'d'} is false defined $hash{'d'} is true defined $hash{'a'} is false exists $hash{'a'} is FALSE (Perl 5 only) grep ($_ eq 'a', keys %hash) is FALSE
See, the whole entry is gone!
This depends on the tied hash's implementation of EXISTS(). For example, there isn't the concept of undef with hashes that are tied to DBM* files. It also means that exists() and defined() do the same thing with a DBM* file, and what they end up doing is not what they do with ordinary hashes.
(contributed by brian d foy)
You can use the keys
or values
functions to reset each
. To simply reset the iterator used by each
without doing anything else, use one of them in void context:
keys %hash; # resets iterator, nothing else. values %hash; # resets iterator, nothing else.
See the documentation for each
in perlfunc.
First you extract the keys from the hashes into lists, then solve the "removing duplicates" problem described above. For example:
my %seen = (); for my $element (keys(%foo), keys(%bar)) { $seen{$element}++; } my @uniq = keys %seen;
Or more succinctly:
my @uniq = keys %{{%foo,%bar}};
Or if you really want to save space:
my %seen = (); while (defined ($key = each %foo)) { $seen{$key}++; } while (defined ($key = each %bar)) { $seen{$key}++; } my @uniq = keys %seen;
Either stringify the structure yourself (no fun), or else get the MLDBM (which uses Data::Dumper) module from CPAN and layer it on top of either DB_File or GDBM_File. You might also try DBM::Deep, but it can be a bit slow.
Use the Tie::IxHash from CPAN.
use Tie::IxHash; tie my %myhash, 'Tie::IxHash'; for (my $i=0; $i<20; $i++) { $myhash{$i} = 2*$i; } my @keys = keys %myhash; # @keys = (0,1,2,3,...)
(contributed by brian d foy)
Are you using a really old version of Perl?
Normally, accessing a hash key's value for a nonexistent key will not create the key.
my %hash = (); my $value = $hash{ 'foo' }; print "This won't print\n" if exists $hash{ 'foo' };
Passing $hash{ 'foo' }
to a subroutine used to be a special case, though. Since you could assign directly to $_[0]
, Perl had to be ready to make that assignment so it created the hash key ahead of time:
my_sub( $hash{ 'foo' } ); print "This will print before 5.004\n" if exists $hash{ 'foo' }; sub my_sub { # $_[0] = 'bar'; # create hash key in case you do this 1; }
Since Perl 5.004, however, this situation is a special case and Perl creates the hash key only when you make the assignment:
my_sub( $hash{ 'foo' } ); print "This will print, even after 5.004\n" if exists $hash{ 'foo' }; sub my_sub { $_[0] = 'bar'; }
However, if you want the old behavior (and think carefully about that because it's a weird side effect), you can pass a hash slice instead. Perl 5.004 didn't make this a special case:
my_sub( @hash{ qw/foo/ } );
Usually a hash ref, perhaps like this:
$record = { NAME => "Jason", EMPNO => 132, TITLE => "deputy peon", AGE => 23, SALARY => 37_000, PALS => [ "Norbert", "Rhys", "Phineas"], };
References are documented in perlref and perlreftut. Examples of complex data structures are given in perldsc and perllol. Examples of structures and object-oriented classes are in perlootut.
(contributed by brian d foy and Ben Morrow)
Hash keys are strings, so you can't really use a reference as the key. When you try to do that, perl turns the reference into its stringified form (for instance, HASH(0xDEADBEEF)
). From there you can't get back the reference from the stringified form, at least without doing some extra work on your own.
Remember that the entry in the hash will still be there even if the referenced variable goes out of scope, and that it is entirely possible for Perl to subsequently allocate a different variable at the same address. This will mean a new variable might accidentally be associated with the value for an old.
If you have Perl 5.10 or later, and you just want to store a value against the reference for lookup later, you can use the core Hash::Util::Fieldhash module. This will also handle renaming the keys if you use multiple threads (which causes all variables to be reallocated at new addresses, changing their stringification), and garbage-collecting the entries when the referenced variable goes out of scope.
If you actually need to be able to get a real reference back from each hash entry, you can use the Tie::RefHash module, which does the required work for you.
(contributed by brian d foy)
The trick to this problem is avoiding accidental autovivification. If you want to check three keys deep, you might naïvely try this:
my %hash; if( exists $hash{key1}{key2}{key3} ) { ...; }
Even though you started with a completely empty hash, after that call to exists
you've created the structure you needed to check for key3
:
%hash = ( 'key1' => { 'key2' => {} } );
That's autovivification. You can get around this in a few ways. The easiest way is to just turn it off. The lexical autovivification
pragma is available on CPAN. Now you don't add to the hash:
{ no autovivification; my %hash; if( exists $hash{key1}{key2}{key3} ) { ...; } }
The Data::Diver module on CPAN can do it for you too. Its Dive
subroutine can tell you not only if the keys exist but also get the value:
use Data::Diver qw(Dive); my @exists = Dive( \%hash, qw(key1 key2 key3) ); if( ! @exists ) { ...; # keys do not exist } elsif( ! defined $exists[0] ) { ...; # keys exist but value is undef }
You can easily do this yourself too by checking each level of the hash before you move onto the next level. This is essentially what Data::Diver does for you:
if( check_hash( \%hash, qw(key1 key2 key3) ) ) { ...; } sub check_hash { my( $hash, @keys ) = @_; return unless @keys; foreach my $key ( @keys ) { return unless eval { exists $hash->{$key} }; $hash = $hash->{$key}; } return 1; }
Since version 5.8.0, hashes can be restricted to a fixed number of given keys. Methods for creating and dealing with restricted hashes are exported by the Hash::Util module.
Perl is binary-clean, so it can handle binary data just fine. On Windows or DOS, however, you have to use binmode
for binary files to avoid conversions for line endings. In general, you should use binmode
any time you want to work with binary data.
Also see "binmode" in perlfunc or perlopentut.
If you're concerned about 8-bit textual data then see perllocale. If you want to deal with multibyte characters, however, there are some gotchas. See the section on Regular Expressions.
Assuming that you don't care about IEEE notations like "NaN" or "Infinity", you probably just want to use a regular expression (see also perlretut and perlre):
use 5.010; if ( /\D/ ) { say "\thas nondigits"; } if ( /^\d+\z/ ) { say "\tis a whole number"; } if ( /^-?\d+\z/ ) { say "\tis an integer"; } if ( /^[+-]?\d+\z/ ) { say "\tis a +/- integer"; } if ( /^-?(?:\d+\.?|\.\d)\d*\z/ ) { say "\tis a real number"; } if ( /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i ) { say "\tis a C float" }
There are also some commonly used modules for the task. Scalar::Util (distributed with 5.8) provides access to perl's internal function looks_like_number
for determining whether a variable looks like a number. Data::Types exports functions that validate data types using both the above and other regular expressions. Thirdly, there is Regexp::Common which has regular expressions to match various types of numbers. Those three modules are available from the CPAN.
If you're on a POSIX system, Perl supports the POSIX::strtod
function for converting strings to doubles (and also POSIX::strtol
for longs). Its semantics are somewhat cumbersome, so here's a getnum
wrapper function for more convenient access. This function takes a string and returns the number it found, or undef
for input that isn't a C float. The is_numeric
function is a front end to getnum
if you just want to say, "Is this a float?"
sub getnum { use POSIX qw(strtod); my $str = shift; $str =~ s/^\s+//; $str =~ s/\s+$//; $! = 0; my($num, $unparsed) = strtod($str); if (($str eq '') || ($unparsed != 0) || $!) { return undef; } else { return $num; } } sub is_numeric { defined getnum($_[0]) }
Or you could check out the String::Scanf module on the CPAN instead.
For some specific applications, you can use one of the DBM modules. See AnyDBM_File. More generically, you should consult the FreezeThaw or Storable modules from CPAN. Starting from Perl 5.8, Storable is part of the standard distribution. Here's one example using Storable's store
and retrieve
functions:
use Storable; store(\%hash, "filename"); # later on... $href = retrieve("filename"); # by ref %hash = %{ retrieve("filename") }; # direct to hash
The Data::Dumper module on CPAN (or the 5.005 release of Perl) is great for printing out data structures. The Storable module on CPAN (or the 5.8 release of Perl), provides a function called dclone
that recursively copies its argument.
use Storable qw(dclone); $r2 = dclone($r1);
Where $r1
can be a reference to any kind of data structure you'd like. It will be deeply copied. Because dclone
takes and returns references, you'd have to add extra punctuation if you had a hash of arrays that you wanted to copy.
%newhash = %{ dclone(\%oldhash) };
(contributed by Ben Morrow)
You can use the UNIVERSAL
class (see UNIVERSAL). However, please be very careful to consider the consequences of doing this: adding methods to every object is very likely to have unintended consequences. If possible, it would be better to have all your object inherit from some common base class, or to use an object system like Moose that supports roles.
Get the Business::CreditCard module from CPAN.
The arrays.h/arrays.c code in the PGPLOT module on CPAN does just this. If you're doing a lot of float or double processing, consider using the PDL module from CPAN instead--it makes number-crunching easy.
See http://search.cpan.org/dist/PGPLOT for the code.
Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and other authors as noted. All rights reserved.
This documentation is free; you can redistribute it and/or modify it under the same terms as Perl itself.
Irrespective of its distribution, all code examples in this file are hereby placed into the public domain. You are permitted and encouraged to use this code in your own programs for fun or for profit as you see fit. A simple comment in the code giving credit would be courteous but is not required.
Version: 5.021011


FTSE jumps on Sino-US trade deal hopes; nationalisation risk hits BT
LONDON, Nov 15 — London’s FTSE 100 followed global peers higher today as hopes of an imminent US-China trade deal were rekindled by comments from a senior US official, while BT slipped after Britain’s opposition party vowed to nationalise parts of the telecoms provider.
The main index rose 0.5 per cent, boosted by miners as well as Asia-focused banks HSBC and Prudential, after White House economic adviser Larry Kudlow said Washington was getting close to a trade pact with Beijing.
Shares of BT shed two per cent, after Labour leader Jeremy Corbyn said his party would nationalise parts of the company’s network if it won power in the December 12 election.
The mid-cap index added 0.2 per cent in early deals. — Reuters


Archives
Here you can find all my previous posts:- Playing with buffer overflow in Rust - June 19, 2022
- 2022-06-19-buffer-overflow-in-rust - June 19, 2022
- Simulating network failures at syscall level - September 4, 2019
- 2019-09-04-simulate-network-failures - September 4, 2019
- When Kafka transactions might fail - April 13, 2019
- 2019-04-13-kafka-transactions - April 13, 2019


[1] replacable battery can add micro memory slot not done correctly it lasted but now it stopepd working after disconnect. requires software program to store pics.
[2] replacable battery can add micro memory slot not done correctly it lasted but now it stopepd working after disconnect. requires software program to store pics too bright even moderately warm leading to good aucio recorder FM recording.


The goal of this project is provide a set of resources for getting started with an embedded system with a GPU and provide them enough background in GPU architecture and GPGPU programming to begin working immediately. The resources will also solve the issue of setting up a working environment. The demos should give a good idea of what this hardware can accomplish.
Product deliverables: a GitHub page, a Project Website, and a bootable USB/Virtual Machine. The physical components would remain with the Oregon State Robotics Club for future club members (and potentially future Senior Capstone groups), while the USB and non-physical deliverables would become a property of the Senior Design Capstone class.
Ultimately, these documents should be enough to get future students quickly started on an embedded system with GPU.
While not strictly required, it is suggested for anyone who is attempting to do a project with GPUs to have knowledge in various coding languages, such as C and C++. Alongside that, a basic knowledge of operating systems would be helpful as well. Also, be sure to review the Background Information page on this website for a full introduction to GPUs.
Graphics Processing Units (GPUs) are a secondary type of computer processor that helps with more specific functions than the main processor. GPUs differ from Central Processing Units (CPUs) by how they complete their tasks. While a CPU is more able to complete complex tasks, it can only complete a few of those at a time. When a multitude of actions need to be completed at once, this can cause massive slowdowns for a CPU. Then the GPU comes in to lighten the CPU’s load.
GPUs are flexible in the amount of tasks they can accomplish by providing the acceleration of work in many industries. GPUs task includes Computational Finance, Climate, Weather and Ocean Modeling, Data Science and Analytics, Deep Learning and Machine learning, Federal, Defense and Intelligence, Manufacturing/AEC: CAD and CAE, Media and Entertainment, Medical Imaging, Oil and Gas, Research: Higher Education and Supercomputing, Safety and Security, Tools and Management.


Before Change
elif len(addresses) > 1:
raise ValueError("Multiple targets might be able to provide {}:\n {}".format(
jvm_package_name, "\n ".join(str(a) for a in addresses)))
return addresses[0].to_address()
@printing_func
@rule(PathGlobs, [Select(JVMPackageName), Select(SourceRoots)])
After Change
@rule(Address, [Select(JVMPackageName), Select(Snapshot)])
def select_package_address(jvm_package_name, snapshot):
Return the Address from the given AddressFamilies which provides the given package.
address_families = yield [Get(AddressFamily, Dir, ds) for ds in snapshot.dir_stats]
addresses = [address for address_family in address_families
for address in address_family.addressables.keys()]
if len(addresses) == 0:
raise ValueError("No targets existed in {} to provide {}".format(


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Dogecoin To The Moon The Game
The BEST Dogecoin game on mobile out there
It's FREE with no ads, I'll make no money out of it.
Let's top chart the app stores to drive adoption of dogecoin!
Share it massively to help promote ÐOGE!


The Inclusive Design Research Centre (IDRC) at OCAD University will be hosting an OER Accessibility Sprint. Experts in the field of Open Educational Resources (OER) will gather to design and develop tools and exemplars that make practical progress in the important agenda of inclusive learning through OER.


Welcome to the “Core” Engine landing page
You can use the following link to view the License this work(s) is registered with.
The “Core” engine is powered by vbscript, powershell, batch, and C#.
ENGINE INFORMATION
| CURRENT VERSION | ARCHITECTURE | NOMENCLATURE | SYSTEM |
|---|---|---|---|
1.09-1.90 |
fLoat.Remap(2018) |
32bit-64bit |
Windows 10 |
Essence
To Download applicable code blocks, select from versioning options below:
:: BLOCK INFORMATION ::
: CURRENT VERSION: 1.09-1.90
: ARCHITECTURE: fLoat.Remap
: NOMENCLATURE: x64
.
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Credits
For Jared my love, Paul, Dylan, and Blake, my brothers and sisters. For anyone who has supported me over the years.


Using BijuJS is very easy!
Open your browser's developer tools console and type in:
BijuJS.hello("world", console.log)
This calls run/hello
with "world"
argument
and console.log
as callback.
The function returns a Promise so you can check your request's status. Then right after you should get a response object that looks like this:
{ "status": "0, "stdout": "Hello, world! It works!\n", "stderr": "" }So, say you want to set up a script named example, then:
That's it!
BijuJS is provided bare-bones, but it's easy to expand upon it.
Consider using MVP.CSS or installing a template rendering engine to quickly develop nice and functional interfaces.


#include <db.h>int memp_fsync(DB_MPOOLFILE *mpf);
The memp_fsync function writes all pages associated with the DB_MPOOLFILE structure, that were marked as modified using memp_fput or memp_fset, back to the source file. If any of the modified pages are also pinned (i.e., currently referenced by this or another process) memp_fsync will ignore them.
The memp_fsync function returns the value of errno on failure, 0 on success, and DB_INCOMPLETE if there were pages which were modified but which memp_fsync was unable to write.
The memp_fsync function may fail and return errno for any of the errors specified for the following Berkeley DB and C library functions: DBmemp->pgin(3), DBmemp->pgout(3), abort(3), close(3), dbenv->db_paniccall(3), fcntl(3), fflush(3), fprintf(3), free(3), fsync(3), getenv(3), getpid(3), getuid(3), isdigit(3), log_compare, log_flush, lseek(3), malloc(3), memcpy(3), memset(3), open(3), pread(3), pwrite(3), qsort(3), read(3), realloc(3), sigfillset(3), sigprocmask(3), stat(3), strerror(3), strlen(3), unlink(3), vfprintf(3), vsnprintf(3), and write(3).


---
layout: post
title: the small science collective is about everyone
date: '2009-02-06T08:51:47+00:00'
tags: []
tumblr_url: http://backlog.robbevan.com/post/76097467/the-small-science-collective-is-about-everyone
---
The Small Science Collective is about everyone, especially non~scientists and non~specialists, thinking about and sharing science through cheap and handy mini-zines.


zipcloak(1) zipcloak(1) NAME zipcloak - encrypt entries in a zipfile SYNOPSIS zipcloak [-d] [-b path] [-h] [-v] [-L] zipfile ARGUMENTS zipfile Zipfile to encrypt entries in OPTIONS -b path --temp-path path Use the directory given by path for the temporary zip file. -d --decrypt Decrypt encrypted entries (copy if given wrong password). -h --help Show a short help. -L --license Show software license. -O path --output-file zipfile Write output to new archive zipfile, leaving original archive as is. -q --quiet Quiet operation. Suppresses some informational messages. -v --version Show version information. DESCRIPTION zipcloak encrypts all unencrypted entries in the zipfile. This is the default action. The -d option is used to decrypt encrypted entries in the zipfile. zipcloak uses original zip encryption which is considered weak. Note: The encryption code of this program is not copyrighted and is put in the public domain. It was originally written in Europe and can be freely distributed from any country including the U.S.A. (Pre‐ viously if this program was imported into the U.S.A, it could not be re-exported from the U.S.A to another country.) See the file README.CR included in the source distribution for more on this. Otherwise, the Info-ZIP license applies. EXAMPLES To be added. BUGS Large files (> 2 GB) and large archives not yet supported. Split archives not yet supported. A work around is to convert the split archive to a single-file archive using zip and then use zipcloak on the single-file archive. If needed, the resulting archive can then be split again using zip. SEE ALSO zip(1), unzip(1) AUTHOR Info-ZIP v3.0 of 8 May 2008 zipcloak(1)


Bigger
Bigger is a movie starring Victoria Justice, Julianne Hough, and Kevin Durand. The inspirational tale of the grandfathers of fitness as we now know it, Joe and Ben Weider. Facing anti-Semitism and extreme poverty, the brothers beat...


The Codepen Times
Woman spends too much time on Codepens despite advice; no plans to stop
Sometimes, Internet users land themselves in an uncommon situation where an app or website can be used for both work and personal situations. Well, a young front-end designer was spending up to 13 hours on the site, Codepen for work and her hobby, which unfortunately, is also coding.
The designer, whose work includes a To-Do Terrarium, clarified, "Well, I didn't have to use it for work but it was already part of my workflow. It just made sense as it was more efficient." The biggest issue, she said, is that she would hop on Codepen for work, but would get distracted by pens made by others in the community for unexpectedly long periods of time, which then causes her to spend even more time on the site.
"I mean, that's terrible right?" she asked. Codepen, which brands itself as the best place to build, test, and discover front-end code, has declined to comment at this time.
Can you get inspired to make your own floor plans?
Making a floor Plan with CSS Grid? Talk about using the wrong tool for the job. But I guess this is what happens when someone isn't happy with any of the floor plans found on Pinterest; she'll start making her own for the eventual home that she will never own. Nevertheless, there's a home office with a large window to look out of pensively during rainy days and a ton of "white space" for the cats to run around.
A pasta menu
Everybody loves pasta. It's impossible to not love them, so here are 15 recipes, served with GSAP. Note the easter egg — the menu icon changes according to the pasta that you choose.
Marvel at a magazine
A tribute of sorts to an era of cool superhero movies, this is a Marvel-themed magazine! Recommended, because it took 45 hours, so you know some serious dedication has been poured into this.
Let's adopt, don't shop.
Explore a style guide and various page layouts for a pet adoption site in the Style Guide collection. Inspired by the Atomic Design principle, this 8-pen collection includes a 404 page concept, an admin dashboard and what a Twitter user calls a 'media card zen garden'. Each pen comes with five (yes, five) color themes, including the precious dark mode.
Toggles
Eight playful toggles to toggle on and off for your amusement. Is it possible to use these on your site and still adhere to assessibility rules? No. But there's a really cute dog one you have to see.
 Shelves, coupons and more!
Get your fill of more CSS Grid items in this collection. There are a total of 32 pens to date... well, 33, if you count this one too. What can you expect in this collection? The hidden gems, in my totally unbiased opinion, are the recreation of the Pac-Man layout and coupons inspired by junk mail. A lot of joke items of things that shouldn't be done in CSS Grid, such as a shelf? Bathroom tiles wtf? and makeup palettes . If you are a cultured person, you will have a chance to enjoy a couple of pens inspired by Harry Potter and Pokemon. On the rare occasion that you are looking at this profile for something you can use in production, you really shouldn't. But, there are some real-world applications, such as the recipe layout, the product catalog, and color palettes for a style guide.


{% extends "blog/base_template.html" %} {% block content %}
I am a 24-year old software engineer from the US, currently living in Switzerland and working at Google. I got my Bachelor's in Computer Science at UMass Amherst and my Master's in Software Engineering at the Technical University of Munich.
I've been coding since I was 15 years old, when my dad forced persuaded me to take an
introductory C++ programming class. I didn't like it—I felt like my brain just wasn't "wired" for coding.
What saved the day was my discovery of Minecraft mods. At the time, people would take the Minecraft source code and add their own code to it. There were some amazing mods—my favorite was one which added industrial machines and factories to the game.
I really wanted to write my own mod, but I would need to become a good programmer first. I began coming up with little programming projects to work on in my spare time, and gradually I started to like it.
I started this blog in 2017 to experiment with Python Flask. Since then I've spent many hundreds of hours writing posts and improving the code. The name "Stefan on Software" comes from one of my favorite blogs, Joel On Software. I strive to produce high-quality content and hope to be as good as Joel some day.
This blog isn't just about software, though. I love traveling, and I regularly write posts about my life abroad. I also like to do small data analysis projects using Python. With the rest of my free time, I play tennis and explore new places in Switzerland. My favorite TV show is Curb Your Enthusiasm, and my favorite video games are Minecraft and Rome Total War.
Feel free to reach out on LinkedIn, or check out my Github.
{% endblock %}


Asynchronous bulk indexing that uses the experimental Kotlin flows. Works similar to the synchronous version except
it fires bulk requests asynchronously. On paper using multiple threads, allows ES to
use multiple Threads to consume bulk requests.
Repository abstraction that allows you to work with indices asynchronously via co-routines.
Makes using bulk request easier. You can use this directly but you probably want to use it via IndexRepository. Implements AutoCloseable
to ensure all operations are processed.
(extensions in package org.elasticsearch.action.search)
(extensions in package org.elasticsearch.client)
Repository abstraction that allows you to work with indices.
Simple implementation of ModelReaderAndWriter that uses a jackson object mapper.
Mutable Map of String to Any that normalizes the keys to use underscores. This is a key component used for
implementing DSLs for querying, mappings, and other things in Elasticsearch. You may also use this to extend the
DSL. Either extend directly or use this via e.g. interface delegation.
Implement this for custom serialization/deserialization of objects in your index. Use this in combination with a IndexRepository.
Represents a page of search results. Returned for non scrolling searches.
Represents scrolling search results. Accessing the searchHits causes pages of results to be retrieved lazily.
Abstraction for search results that applies to both scrolling and non scrolling searches.
(extensions in package io.inbot.eskotlinwrapper)
Action listener that can be used with to adapt the async methods across the java client to co-routines.


{% extends "base.html" %} {% set baseurl = ".." %} {% block header %} {% endblock %} {% block content %}
This library provides realtime image effects using WebGL. There are three parts to glfx.js:
There are two caveats to glfx.js. First, WebGL is a new technology that is only available in the latest browsers and it will be quite a while before the majority of users have it. Second, due to the same origin policy, JavaScript is only allowed to read images that originate from the same domain as the script reading them, so you may have to host the images you modify.
This HTML fragment is all you need to use the API. Copy and paste it into an empty index.html document, make sure that directory also contains glfx.js and an image named image.jpg, and open index.html. You should see the image with the ink filter applied.
<script src="glfx.js"></script> <script> window.onload = function() { // try to create a WebGL canvas (will fail if WebGL isn't supported) try { var canvas = fx.canvas(); } catch (e) { alert(e); return; } // convert the image to a texture var image = document.getElementById('image'); var texture = canvas.texture(image); // apply the ink filter canvas.draw(texture).ink(0.25).update(); // replace the image with the canvas image.parentNode.insertBefore(canvas, image); image.parentNode.removeChild(image); // Note: instead of swapping the <canvas> tag with the <img> tag // as done above, we could have just transferred the contents of // the image directly: // // image.src = canvas.toDataURL('image/png'); // // This has two disadvantages. First, it is much slower, so it // would be a bad idea to do this repeatedly. If you are going // to be repeatedly updating a filter it's much better to use // the <canvas> tag directly. Second, this requires that the // image is hosted on the same domain as the script because // JavaScript has direct access to the image contents. When the // two tags were swapped using the previous method, JavaScript // actually doesn't have access to the image contents and this // does not violate the same origin policy. }; </script> <img id="image" src="image.jpg">
var canvas = fx.canvas();
Before you can apply any filters you will need a canvas, which stores the result of the filters you apply. Canvas creation is done through fx.canvas(), which creates and returns a new WebGL <canvas> tag with additional methods specific to glfx.js. This call will throw an error message if the browser doesn't support WebGL.
canvas.draw(texture);
This replaces the internal contents of the canvas with the image stored in texture. All filter operations take place in a chain that starts with canvas.draw() and ends with canvas.update().
texture |
Stores image data, the result of calling fx.texture(). |
canvas.update();
This replaces the visible contents of the canvas with the internal image result. For efficiency reasons, the internal image buffers are not rendered to the screen every time a filter is applied, so you will need to call update() on your canvas after you have finished applying the filters to be able to see the result. All filter operations take place in a chain that starts with canvas.draw() and ends with canvas.update().
var texture = canvas.texture(element);
Creates a texture that initially stores the image from an HTML element. Notice that texture() is a method on a canvas object, which means if you want to use the same image on two canvas objects you will need two different textures, one for each canvas.
element |
The HTML element to store in the texture, either an <img>, a <canvas>, or a <video>. |
texture.loadContentsOf(element);
Loads the image from an HTML element into the texture. This is more efficient than repeatedly creating and destroying textures.
element |
The HTML element to store in the texture, either an <img>, a <canvas>, or a <video>. |
texture.destroy();
Textures will be garbage collected eventually when they are no longer referenced, but this method will free GPU resources immediately.


Hidden Figures
Fantastic Beasts
All Movies Bubble Chart
All Movies Bar Chart
All Characters
Characters by Gender
Batman vs. Superman
Civil War
Deadpool
Fantastic Beasts
Finding Dory
Junglebook
Rogue One
Secret Life of Pets
Suicide Squad
Zootopia


{% extends "base.html" %} {% block bodydata %} data-project-id="{{project.id}}"{% endblock %} {% block title %} | Project: {{project.name}}{% endblock %} {% block main %}
Deleting a project can not be undone and will delete all data contributed to the project.
Delete this project


7. Pulse Width Modulation¶
Pulse width modulation (PWM) is a way to get an artificial analog output on a digital pin. It achieves this by rapidly toggling the pin from low to high. There are two parameters associated with this: the frequency of the toggling, and the duty cycle. The duty cycle is defined to be how long the pin is high compared with the length of a single period (low plus high time). Maximum duty cycle is when the pin is high all of the time, and minimum is when it is low all of the time.
On the ESP8266 the pins 0, 2, 4, 5, 12, 13, 14 and 15 all support PWM. The limitation is that they must all be at the same frequency, and the frequency must be between 1Hz and 1kHz.
To use PWM on a pin you must first create the pin object, for example:
>>> import machine
>>> p12 = machine.Pin(12)
Then create the PWM object using:
>>> pwm12 = machine.PWM(p12)
You can set the frequency and duty cycle using:
>>> pwm12.freq(500)
>>> pwm12.duty(512)
Note that the duty cycle is between 0 (all off) and 1023 (all on), with 512 being a 50% duty. Values beyond this min/max will be clipped. If you print the PWM object then it will tell you its current configuration:
>>> pwm12
PWM(12, freq=500, duty=512)
You can also call the freq()
and duty()
methods with no arguments to
get their current values.
The pin will continue to be in PWM mode until you deinitialise it using:
>>> pwm12.deinit()
7.1. Fading an LED¶
Let’s use the PWM feature to fade an LED. Assuming your board has an LED connected to pin 2 (ESP-12 modules do) we can create an LED-PWM object using:
>>> led = machine.PWM(machine.Pin(2), freq=1000)
Notice that we can set the frequency in the PWM constructor.
For the next part we will use timing and some math, so import these modules:
>>> import time, math
Then create a function to pulse the LED:
>>> def pulse(l, t):
... for i in range(20):
... l.duty(int(math.sin(i / 10 * math.pi) * 500 + 500))
... time.sleep_ms(t)
You can try this function out using:
>>> pulse(led, 50)
For a nice effect you can pulse many times in a row:
>>> for i in range(10):
... pulse(led, 20)
Remember you can use ctrl-C to interrupt the code.
7.2. Control a hobby servo¶
Hobby servo motors can be controlled using PWM. They require a frequency of 50Hz and then a duty between about 40 and 115, with 77 being the centre value. If you connect a servo to the power and ground pins, and then the signal line to pin 12 (other pins will work just as well), you can control the motor using:
>>> servo = machine.PWM(machine.Pin(12), freq=50)
>>> servo.duty(40)
>>> servo.duty(115)
>>> servo.duty(77)