====== Perl Cheat Sheet ======

[[http://www.perl.org/ | Perl]] is a highly capable, feature-rich programming language with over 25 years of development. These notes follow the path of the [[http://www.amazon.com/Learning-Perl-Randal-L-Schwartz/dp/1449303587 | Learning Perl]] book.

  * First line should be #!/usr/bin/perl or #!/usr/bin/env perl
  * Perl compiles to byte-code before executing
  * Do not use an extension for scripts.
  * To specify a minimum version use "use 5.010;"
  * Semicolons (;) required to separate statements
  * "perl -w" turns on warnings for entire program. For just the current file use "use warnings;"
  * "use diagnostics;" adds explanations to warnings
  * "use strict;" requires variable declaration
  * Comments start with # (no block comments)


===== Scalar Variables =====

  * Scalars are numbers or strings (or undefined or references), used interchangeably.
  * Scalar variables start with $ and a letter or underscore, but can contain letters (including unicode), numbers or underscores.
  * Scalar assignment looks like  $a = 3; or $a .= "suffix"; or $a %%**%%= 3;
  * Recommended to use all lowercase variable names with underscores for word separation e.g. $var_name
  * print takes a single scalar or a list of scalars (separated by commas)
  * When a scalar is interpreted as a boolean, the following are //false// : 0, '0', %%''%%, undefined .
  * !! is a handy shortcut to convert any scalar to 0 or 1 (to represent a boolean)

===== Numbers =====

  * All numbers are stored in the same format e.g.-6.5e24, 037 (octal), 0x2a13b (hex), 0b11010 (binary)
  * Underscores for readability are ignored e.g. 0x1377_0B77
  * Arithmetic operators are * / + - % (modulus) ** (exponentiation)
  * Comparison operators are < <= == >= > !=

===== Strings =====
  * To use unicode in source code - "use utf8;"
  * Single-quoted literals '⅚∞☃☠' can contain any character except single-quote (use \') and backslash (use \\).
  * Double-quoted strings can contain control-characters starting with a backslash and are variable interpolated e/g/ "${var}s $var\n".
  * . is for concatenation, x for string repetition.
  * To insert a character by code - chr(0x05d0). To convert a character to its code - ord('א')
  *  String comparison operators are lt, le, eq, ge, gt, and ne

===== Control Structures =====

  * if-elsif-else <code perl>if ($a == $b) {
  a = 0;
} elsif ($a > $b) {
  a = 1;
} else {
  a = -1;
}</code>
  * while loop <code perl>$count=0;
while ($count < 10) {
    $count += 2;
}</code>

===== Input/Output =====

  * Read a line of input - ''$line = <STDIN>;''
  * ''chomp'' removes a newline e.g. ''chomp($line=<STDIN>);''