Perl 6 One Liners
This book is a work in progress. I hope you find it interesting, maybe even useful! If you would like to contribute, feedback, issues and new or improved regexes are all welcome!
AUTHOR
David Farrell PerlTricks.com
VERSION
Version 0.01
LICENSE
FreeBSD - see LICENSE
CONTRIBUTORS
- Alexander Moquin
- Bruce Gray
- Cale
- Carl Mรคsak
- David H. Adler
- FROGGS
- Helmut Wollmersdorfer
- Hugh Simpson
- japhb
- Larry Wall
- Mathieu Gagnon
- Matt Oates
- Moritz Lenz
- Mouq
- Salve J Nilsen
- Sam S
- Skids
- timotimo
THANKS
Inspired by Peteris Krumins Perl 5 examples file. He literally wrote the book on Perl 5 one liners.
The wonderful folks on #Perl6 irc.
CONTENTS
- Introduction
- Tutorial
- File Spacing
- Line Numbering
- Calculations
- String Creation and Array Creation
- Text Conversion and Substitution
- Text Analysis
- Selective Line Printing
- Data Transformation With Pipes (in progress)
- WWW (in progress)
- Converting for Windows
INTRODUCTION
One thing that sets Perl apart from other languages is the ability to write small programs in a single line of code, known as a "one liner". It's often faster to type a program directly into the terminal than to write a throwaway script. And one liners are powerful too; they're fully fledged programs which can load external libraries but also integrate into the terminal. You can pipe data in or out of a one liner.
Like Perl 5, Perl 6 supports one liners. And just like Perl 6 cleaned up Perl 5's warts elsewhere, the one liner syntax is also better. It's cleaner with fewer special variables and options to memorize. This book provides many useful examples of Perl 6 one liners that can do everything from finding duplicate lines in a file to running a web server. Although Perl 6 has fewer special variables, because of its advanced object oriented syntax most of the one liners are shorter in Perl 6 than their Perl 5 equivalent.
This book can be read in a number of ways. If you're new to one liners, start with the tutorial. It walks you through the core concepts of a one liner; don't worry - it's really very simple once you get the hang of it. If you're familiar with Perl, Bash or Sed/Awk, you can probably get stuck in to the examples right away. Feel free to skim and scan the material for whatever piques your interest. If you don't understand some code, try it out in the terminal! Included in this repo is the ubiquitous example.txt file which is used in many of the one liners.
Programming with one liners is just one paradigm that Perl 6 excels in. There's a beauty in the brevity of this code, but whilst you're learning a productive skill, remember that you're also learning the ropes of a powerful new programming language. Check out the perl6.org website for the official documentation.
TUTORIAL
To get started with one liners, all you really need to understand is the -e option. This tells Perl to execute what follows as a program. For example:
perl6 -e 'say "Hello, World!"'
Let's step through this code. perl6 invokes the Perl 6 program, -e tells Perl 6 to execute and 'say "Hello, World!"' is the program. Every program must be surrounded in single quotes (except on Windows, see Converting for Windows). To run the one-liner, just type it into the terminal:
> perl6 -e 'say "Hello, World!"'
Hello, World!
If you want to load a file, just add the path to the file after the program code:
perl6 -e 'for (lines) { say $_ }' /path/to/file.txt
This program prints every line in /path/to/file.txt. You may know that $_ is the default variable, which in this case is the current line being looped through. lines is a list that is automatically created for you whenever you pass a filepath to a one-liner. Now let's re-write that one liner, step-by-step. These are all equivalent:
perl6 -e 'for (lines) { say $_ }' /path/to/file.txt
perl6 -e 'for (lines) { $_.say }' /path/to/file.txt
perl6 -e 'for (lines) { .say }' /path/to/file.txt
perl6 -e '.say for (lines)' /path/to/file.txt
perl6 -e '.say for lines' /path/to/file.txt
Just like $_ is the default variable, methods called on the default variable can omit the variable reference. They become default methods. So $_.say becomes .say. This brevity pays off with one liners - it's less typing!
The -n option changes the behavior of the program: it executes the code once for every line of the file. So uppercase and print every line of /path/to/file.txt you can type:
perl6 -ne '.uc.say' /path/to/file.txt
The -p option is just like -n except that it will automatically print $_. So another way we could uppercase a file would be:
perl6 -pe '$_ = .uc' /path/to/file.txt
Or two shorter versions that do the same thing:
perl6 -pe '.=uc' /path/to/file.txt
perl6 -pe .=uc /path/to/file.txt
In the second example we were able to completely remove the surrounding single quotes. This is a rare scenario, but in the event your one liner has no spaces and no sigils or quotes in it, you can usually remove the outer quotes.
The -n and -p options are really useful. There are lots of example one-liners that use them in this book.
The final thing you should know is how to load a module. This is really powerful as you can extend Perl 6's capabilities by importing external libraries. The -M switch stands for load module:
perl6 -M URI::Encode -e 'say uri_encode("example.com/10 ways to crush it with Perl 6")'
This: -M URI::Encode loads the URI::Encode module, which exports the uri_encode subroutine. You can use -M more than once if you want to load more than one module:
perl6 -M URI::Encode -M URI -e '<your code here>'
What if you have a local module, that is not installed yet? Easy, just pass use the -I switch to include the directory:
perl6 -I lib -M URI::Encode -e '<your code here>'
Now Perl 6 will search for URI::Encode in lib as well as the standard install locations.
To get a list of Perl 6 command line switches, use the -h option for help:
perl6 -h
This prints a nice summary of the available options.
FILE SPACING
Double space a file
perl6 -pe '$_ ~= "\n"' example.txt
N-space a file (e.g. quadruple space)
perl6 -pe '$_ ~= "\n" x 4' example.txt
Add a blank line before every line
perl6 -pe 'say ""' example.txt
Remove all blank lines
perl6 -ne '.say if /\S/' example.txt
perl6 -ne '.say if .chars' example.txt
Remove all consecutive blank lines, leaving just one
perl6 -e '$*ARGFILES.slurp.subst(/\n+/, "\n\n", :g).say' example.txt
LINE NUMBERING
Number all lines in a file
perl6 -ne 'say "{++$} $_"' example.txt
perl6 -ne 'say $*ARGFILES.lines.kv ~ " $_"' example.txt
Number only non-empty lines in a file
perl6 -pe '$_ = "{++$} $_" if /\S/' example.txt
Number all lines but print line numbers only for non-empty lines
perl6 -pe '$_ = $*ARGFILES.lines.kv ~ " $_" if /\S/' example.txt
Print the total number of lines in a file (emulate wc -l)
perl6 -e 'say lines.elems' example.txt
perl6 -e 'say lines.Int' example.txt
perl6 -e 'lines.Int.say' example.txt
Print the number of non-empty lines in a file
perl6 -e 'lines.grep(/\S/).elems.say' example.txt
Print the number of empty lines in a file
perl6 -e 'lines.grep(/^\s*$/).elems.say' example.txt
CALCULATIONS
Check if a number is a prime
perl6 -e 'say "7 is prime" if 7.is-prime'
Print the sum of all the fields on a line
perl6 -ne 'say [+] .split("\t")'
Print the sum of all the fields on all lines
perl6 -e 'say [+] lines.split("\t")'
Shuffle all fields on a line
perl6 -ne '.split("\t").pick(*).join("\t").say'
Find the lexically minimum element on a line
perl6 -ne '.split("\t").min.say'
Find the lexically minimum element over all the lines
perl6 -e 'lines.split("\t").min.say'
Find the lexically maximum element on a line
perl6 -ne '.split("\t").max.say'
Find the lexically maximum element over all the lines
perl6 -e 'lines.split("\t").max.say'
Find the numerically minimum element on a line
perl6 -ne '.split("\t")ยป.Numeric.min.say'
Find the numerically maximum element on a line
perl6 -ne '.split("\t")ยป.Numeric.max.say'
Replace each field with its absolute value
perl6 -ne '.split("\t").map(*.abs).join("\t").say'
Find the total number of letters on each line
perl6 -ne '.chars.say' example.txt
Find the total number of words on each line
perl6 -ne '.words.elems.say' example.txt
Find the total number of elements on each line, split on a comma
perl6 -ne '.split(",").elems.say' example.txt
Find the total number of fields (words) on all lines
perl6 -e 'say lines.split("\t").elems' #fields
perl6 -e 'say lines.words.elems' example.txt #words
Print the total number of fields that match a pattern
perl6 -e 'say lines.split("\t").comb(/pattern/).elems' #fields
perl6 -e 'say lines.words.comb(/pattern/).elems' #words
Print the total number of lines that match a pattern
perl6 -e 'say lines.grep(/in/).elems'
Print the number PI to n decimal places (e.g. 10)
perl6 -e 'say pi.fmt("%.10f");'
Print the number PI to 15 decimal places
perl6 -e 'say ฯ'
Print the number E to n decimal places (e.g. 10)
perl6 -e 'say e.fmt("%.10f");'
Print the number E to 15 decimal places
perl6 -e 'say e'
Print UNIX time (seconds since Jan 1, 1970, 00:00:00 UTC)
perl6 -e 'say time'
Print GMT (Greenwich Mean Time) and local computer time
perl6 -MDateTime::TimeZone -e 'say to-timezone("GMT",DateTime.now)'
perl6 -e 'say DateTime.now'
Print local computer time in H:M:S format
perl6 -e 'say DateTime.now.map({$_.hour, $_.minute, $_.second.round}).join(":")'
Print yesterday's date
perl6 -e 'say DateTime.now.earlier(:1day)'
Print date 14 months, 9 days and 7 seconds ago
perl6 -e 'say DateTime.now.earlier(:14months).earlier(:9days).earlier(:7seconds)'
Prepend timestamps to stdout (GMT, localtime)
tail -f logfile | perl6 -MDateTime::TimeZone -ne 'say to-timezone("GMT",DateTime.now) ~ "\t$_"'
tail -f logfile | perl6 -ne 'say DateTime.now ~ "\t$_"'
Calculate factorial of 5
perl6 -e 'say [*] 1..5'
Calculate greatest common divisor
perl6 -e 'say [gcd] @list_of_numbers'
Calculate GCM of numbers 20 and 35 using Euclid's algorithm
perl6 -e 'say (20, 35, *%* ... 0)[*-2]'
Calculate least common multiple (LCM) of 20 and 35
perl6 -e 'say 20 lcm 35'
Calculate LCM of 20 and 35 using Euclid's algorithm: n*m/gcd(n,m)
perl6 -e 'say 20 * 35 / (20 gcd 35)'
Generate 10 random numbers between 5 and 15 (excluding 15)
perl6 -e '.say for (5..^15).roll(10)'
Find and print all permutations of a list
perl6 -e 'say .join for [1..5].permutations'
Generate the power set
perl6 -e '.say for <1 2 3>.combinations'
Convert an IP address to unsigned integer
perl6 -e 'say :256["127.0.0.1".comb(/\d+/)]'
perl6 -e 'say +":256[{q/127.0.0.1/.subst(:g,/\./,q/,/)}]"'
perl6 -e 'say Buf.new(+ยซ"127.0.0.1".split(".")).unpack("N")'
Convert an unsigned integer to an IP address
perl6 -e 'say join ".", @(pack "N", 2130706433)'
perl6 -e 'say join ".", map { ((2130706433+>(8*$_))+&0xFF) }, (3...0)'
STRING CREATION AND ARRAY CREATION
Generate and print the alphabet
perl6 -e '.say for "a".."z"'
Generate and print all the strings from "a" to "zz"
perl6 -e '.say for "a".."zz"'
Convert a integer to hex
perl6 -e 'say 255.base(16)'
perl6 -e 'say sprintf("%x", 255)'
Print an int to hex translation table
perl6 -e 'say sprintf("%3i => %2x", $_, $_) for 0..255'
Percent encode an integer
perl6 -e 'say sprintf("%%%x", 255)'
Generate a random 10 a-z character string
perl6 -e 'print roll 10, "a".."z"'
perl6 -e 'print roll "a".."z": 10'
Generate a random 15 ASCII Character password
perl6 -e 'print roll 15, "0".."z"'
perl6 -e 'print roll "0".."z": 15'
Create a string of specific length
perl6 -e 'print "a" x 50'
Generate and print an array of even numbers from 1 to 100
perl6 -e '(1..100).grep(* %% 2).say'
Find the length of the string
perl6 -e '"storm in a teacup".chars.say'
Find the number of elements in an array
perl6 -e 'my @letters = "a".."z"; @letters.Int.say'
TEXT CONVERSION AND SUBSTITUTION
ROT 13 a file
perl6 -pe 'tr/A..Za..z/N..ZA..Mn..za..m/' example.txt
Base64 encode a string
perl6 -MMIME::Base64 -ne 'print MIME::Base64.encode-str($_)' example.txt
Base64 decode a string
perl6 -MMIME::Base64 -ne 'print MIME::Base64.decode-str($_)' base64.txt
URL-escape a string
perl6 -MURI::Encode -le 'say uri_encode($string)'
URL-unescape a string
perl6 -MURI::Encode -le 'say uri_decode($string)'
HTML-encode a string
perl6 -MHTML::Entity -e 'print encode-entities($string)'
HTML-decode a string
perl6 -MHTML::Entity -e 'print decode-entities($string)'
Convert all text to uppercase
perl6 -pe '.=uc' example.txt
perl6 -ne 'say .uc' example.txt
Convert all text to lowercase
perl6 -pe '.=lc' example.txt
perl6 -ne 'say .lc' example.txt
Uppercase only the first word of each line
perl6 -ne 'say s/(\w+){}/{$0.uc}/' example.txt
Invert the letter case
perl6 -pe 'tr/a..zA..Z/A..Za..z/' example.txt
perl6 -ne 'say tr/a..zA..Z/A..Za..z/.after' example.txt
Camel case each line
perl6 -ne 'say .wordcase' example.txt
Strip leading whitespace (spaces, tabs) from the beginning of each line
perl6 -ne 'say .trim-leading' example.txt
Strip trailing whitespace (space, tabs) from the end of each line
perl6 -ne 'say .trim-trailing' example.txt
Strip whitespace from the beginning and end of each line
perl6 -ne 'say .trim' example.txt
Convert UNIX newlines to DOS/Windows newlines
perl6 -ne 'print .subst(/\n/, "\r\n")' example.txt
Convert DOS/Windows newlines to UNIX newlines
perl6 -ne 'print .subst(/\r\n/, "\n")' example.txt
Find and replace all instances of "ut" with "foo" on each line
perl6 -pe 's:g/ut/foo/' example.txt
Find and replace all instances of "ut" with "foo" on each line that contains "lorem"
perl6 -pe 's:g/ut/foo/ if /Lorem/' example.txt
Convert a file to JSON
perl6 -M JSON::Tiny -e 'say to-json(lines)' example.txt
Pick 5 random words from each line of a file
perl6 -ne 'say .words.pick(5)' example.txt
TEXT ANALYSIS
Print n-grams of a string
perl6 -e 'my $n=2; say "banana".comb.rotor($n => 1 - $n)ยป.join()'
Print unique n-grams
perl6 -e 'my $n=2; say "banana".comb.rotor($n => 1 - $n)ยป.join().Set.sort'
Print occurrence counts of n-grams
perl6 -e 'my $n=2; say "banana".comb.rotor($n => 1 - $n)ยป.join().Bag.sort.join("\n")'
Print occurrence counts of words (1-grams)
perl6 -e 'say lines[0].words.join().Bag.sort.join("\n")' example.txt
Print Dice similarity coefficient based on sets of 1-grams
perl6 -e 'my $a="banana".comb;my $b="anna".comb;say ($a (&) $b)/($a.Set + $b.Set)'
Print Jaccard similarity coefficient based on 1-grams
perl6 -e 'my $a="banana".comb;my $b="anna".comb;say ($a (&) $b) / ($a (|) $b)'
Print overlap coefficient based on 1-grams
perl6 -e 'my $a="banana".comb;my $b="anna".comb;say ($a (&) $b)/($a.Set.elems,$b.Set.elems).min'
Print cosine similarity based on 1-grams
perl6 -e 'my $a="banana".comb;my $b="anna".comb;say ($a (&) $b)/($a.Set.elems.sqrt*$b.Set.elems.sqrt)'
Build an index of characters within a string and print it
perl6 -e 'say {}.push: %("banana".comb.pairs).invert'
Build an index of words within a line and print it
perl6 -e '({}.push: %(lines[0].words.pairs).invert).sort.join("\n").say' example.txt
SELECTIVE LINE PRINTING
Print the first line of a file (emulate head -1)
perl6 -ne '.say;exit' example.txt
perl6 -e 'lines[0].say' example.txt
perl6 -e 'lines.shift.say' example.txt
Print the first 10 lines of a file (emulate head -10)
perl6 -pe 'exit if ++$ > 10' example.txt
perl6 -ne '.say if ++$ < 11' example.txt
Print the last line of a file (emulate tail -1)
perl6 -e 'lines.pop.say' example.txt
Print the last 5 lines of a file (emulate tail -5)
perl6 -e '.say for lines[*-5..*]' example.txt
Print only lines that contain vowels
perl6 -ne '/<[aeiou]>/ && .print' example.txt
Print lines that contain all vowels
perl6 -ne '.say if .comb (>=) <a e i o u>' example.txt
perl6 -ne '.say if .comb โ <a e i o u>' example.txt
Print lines that are 80 chars or longer
perl6 -ne '.print if .chars >= 80' example.txt
perl6 -ne '.chars >= 80 && .print' example.txt
Print only line 2
perl6 -ne '.print if ++$ == 2' example.txt
Print all lines except line 2
perl6 -pe 'next if ++$ == 2' example.txt
Print all lines 1 to 3
perl6 -ne '.print if (1..3).any == ++$' example.txt
Print all lines between two regexes (including lines that match regex)
perl6 -ne '.print if /^Lorem/../laborum\.$/' example.txt
Print the length of the longest line
perl6 -e 'say lines.max.chars' example.txt
perl6 -ne 'state $l=0; $l = .chars if .chars > $l;END { $l.say }' example.txt
Print the longest line
perl6 -e 'say lines.max' example.txt
perl6 -e 'my $l=""; for (lines) {$l = $_ if .chars > $l.chars};END { $l.say }' example.txt
Print all lines that contain a number
perl6 -ne '.say if /\d/' example.txt
perl6 -e '.say for lines.grep(/\d/)' example.txt
perl6 -ne '/\d/ && .say' example.txt
perl6 -pe 'next if ! $_.match(/\d/)' example.txt
Find all lines that contain only a number
perl6 -ne '.say if /^\d+$/' example.txt
perl6 -e '.say for lines.grep(/^\d+$/)' example.txt
perl6 -ne '/^\d+$/ && .say' example.txt
perl6 -pe 'next if ! $_.match(/^\d+$/)' example.txt
Print every even line
perl6 -ne '.say if ++$ %% 2' example.txt
Print every odd line
perl6 -ne '.say if ++$ !%% 2' example.txt
Print all lines that repeat
perl6 -ne 'state %l;.say if ++%l{$_}==2' example.txt
Print unique lines
perl6 -ne 'state %l;.say if ++%l{$_}==1' example.txt
Print the first field (word) of every line (emulate cut -f 1 -d ' ')
perl6 -ne '.words[0].say' example.txt
DATA TRANSFORMATION WITH PIPES
Perl 6 programs integrate straight into the command line. You can pipe data in-to and out-of a one liner by using the pipe | character. For piping data in, Perl 6 automatically sets STDIN to $*IN. Just like with files, data piped in can be looped through using -n and is also available in lines. To pipe data out of a one liner just use print or say.
JSON-encode a list of all files in the current directory
ls | perl6 -M JSON::Tiny -e 'say to-json(lines)'
Print a random sample of approx 5% of lines in a file
perl6 -ne '.say if 1.rand <= 0.05' /usr/share/dict/words
Color conversion, HTML to RGB
echo "#ffff00" | perl6 -ne '.comb(/\w\w/).map({:16($_)}).say'
Color conversion, RGB to HTML
echo "#ffff00" | perl6 -ne '.comb(/\w\w/).map({:16($_)}).say'
WWW
Download a webpage
perl6 -M HTTP::UserAgent -e 'say HTTP::UserAgent.new.get("google.com").content'
Download a webpage and strip out the HTML
wget -O - "http://perl6.org" | perl6 -ne 's:g/\<.+?\>//.say'
Download a webpage, strip out and decode the HTML
wget -O - "http://perl6.org" | perl6 -MHTML::Strip -ne 'strip_html($_).say'
Launch a simple web server
perl6 -M HTTP::Server::Simple -e 'HTTP::Server::Simple.new.run'
CONVERTING FOR WINDOWS
Running one liners on Windows is a piece of cake once you know the rules of the road. One liners work on both cmd.exe and PowerShell. The cardinal rule is: replace the outer single-quotes with double quotes and use the interpolated quoting operator qq// for quoting strings inside a one liner. For non-interpolated quoting, you can use single-quotes. Let's look at some examples.
Here's a simple one liner to print the time:
perl6 -e 'say DateTime.now'
To run on Windows, we just replace the single quotes with double quotes:
perl6 -e "say DateTime.now"
This one liner appends a newline to every line in a file, using an interpolated string:
perl6 -pe '$_ ~= "\n"' example.txt
On Windows this should be written as:
perl6 -pe "$_ ~= qq/\n/" example.txt
In this case we want to interpolate \n as a newline and not literally add a backslash and an "n" to the line, so we have to use qq. But you can usually use single-quotes within a one liner so:
perl6 -e 'say "Hello, World!"'
On Windows can be written as:
perl6 -e "say 'hello, World!'"
Simple output redirection works like it does on Unix-based systems. This one liner prints an ASCII character index table to a file using >:
perl6 -e "say .chr ~ ' ' ~ $_ for 0..255" > ascii_codes.txt
When using > if the file doesn't exist, it will be created. If the file does exist, it will be overwritten. If you'd rather append to a file, use >> instead.