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--- notes:perl_cheat_sheet [2026/11/03 12:09]
47.79.201.214 old revision restored (2026/09/06 20:00)
+++ notes:perl_cheat_sheet [2026/11/03 15:51] (current)
216.73.217.9 old revision restored (2026/11/02 18:14)
@@ Line 12: / Line 12: @@
   * "use strict;" requires variable declaration
   * Comments start with # (no block comments)
-  * Parenthesis are optional unless part of syntax.
+===== 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 =====
@@ Line 18: / Line 28: @@
   * 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)
+  * 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 \\).
@@ Line 29: / Line 38: @@
   * 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
-===== Scalar Variables =====
-  * Scalars are numbers or strings (or undefined or references), used interchangeably.
-  * $calar 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. $var_name
-  * print takes a single scalar or a list of scalars (separated by commas)
-  * When a scalar is interpreted as a boolean, the following are //false// : 0, '0', %%''%%, undefined .
-  * !! is a handy shortcut to convert any scalar to 0 or 1 (to represent a boolean)
-  * Variables have value ''undef'' before being assigned. ''undef'' acts as a 0 or "" as needed, but will throw a warning if printed.
-  * ''defined()'' checks if a variable has been defined. Can also set a variable to ''undef''.
-===== Lists and Arrays =====
-  * A list is an ordered set of elements (each of which is a scalar value), starting with position 0.
-  * @rrays are variables that store a list (separate namespace from scalar variables). @x refers to entire array x.
-  * Undefined arrays start out as ''()'', the empty list and not ''undef''.
-  * To access an element of an array - ''$myarr[0]'' - ''undef'' if never set.
-  * Index of last element is in ''$#arr''
-  * Negative array indices wrap around (only once) so -1 refers to last element.
-  * Literal lists - ''('abc','def')'' or ''(1..6)'' (integers 1 to 6) or ''qw(abc def)'' or ''qw#abc def#'' (quoted by whitespace).
-  * Can assign list values to variables e.g. <code perl>($fred, $barney, $dino) = ("flintstone", "rubble", undef);
-($fred, $barney) = ($barney, $fred); # swap those values</code>
-  * ''push'' adds element(s) to **end** of array. ''pop'' removes a single element and returns it.
-  * ''unshift'' adds element(s) to **start** of array. ''shift'' removes a single element and returns it.
-  * ''splice'' removes elements from middle of array, returns them and optionally replaces them <code perl>splice @arr, start, len, @newelems</code>
-  * ''sort'' and ''reverse'' functions return the modified list (can be saved to original array variable).
-  * Expressions parsed in either a scalar context or a list context. Scalars are promoted to single-element lists in list context.
-  * List functions may return different scalars - array variables return number of elements. The ''scalar'' function forces a scalar context e.g. for print function.
 ===== Control Structures =====
@@ Line 72: / Line 51: @@
 while ($count < 10) {
     $count += 2;
-}</code>
-  * foreach loop <code perl>foreach my $rock (@rocks) {
-  # modifications to $rock modify the list element
-  # $_ is used if loop variable is omitted
 }</code>
@@ Line 82: / Line 57: @@
   * Read a line of input - ''$line = <STDIN>;''
   * ''chomp'' removes a newline e.g. ''chomp($line=<STDIN>);''
-  * Assigning <STDIN> to a list reads all input up till EOF e.g. <code perl> chmop(@lines = <STDIN>);</code>
-===== User Subroutines =====
-  * Subroutines are in their own namespace and are typically called using ''&mysub'' (sometimes the ampersand can be omitted).
-  * Subroutines can be defined anywhere e.g. <code perl> sub mysub {
-  my($m, $n) = @_
-  $m + $n;
-} </code>
-  * The value of the last expression evaluated is returned. But ''return $a;'' can be used to return immediately.
-  * Arguments are in the list @_ . If ''&mysub;'' is used, the parent's argument list is inherited.
-  * Lexical scoped variables can be used in any block by prefixing with ''my''.
-  * Ampersand is optional if subroutine has previously been declared or if parenthesis are used. Ampersand is not optional if built-in subroutine is being overridden.

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