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Perl

682 problems50 sections📅 2026 curriculum

Learn Perl by typing pragmatic, idiomatic code.

Practice Perl by typing its signature tools: powerful regular expressions, hashes and arrays, the sigils ($, @, %) that mark context, and text-munging one-liners. Each snippet is idiomatic Perl, and an AI tutor explains every line — how context changes what an expression returns, what a regex capture grabs — so Perl's terseness becomes readable as you build speed.

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Run Perl on your machine

1. Install the toolchain

perl is preinstalled on macOS/Linux # or: brew install perl

2. Save your code as hello.pl, then compile & run

perl hello.pl

Official install docs ↗

progress by section

1Fundamentals0/5start →

Hello, Perl Scalar bindings Conditionals Loops and ranges Subroutines

2Strings In Depth0/18start →

String length Change case Concatenate with .String interpolation Find with index Join a list printf directly Repeat with x Reverse a string Split into a list Substitute with s///Extract with substr Heredoc blocks Match and capture Format with sprintf Replace with 4-arg substr Transliterate with tr Global substitute

3Values & References0/18start →

Array reference Hash reference What ref() reports Scalar reference foreach aliases Anonymous array Anonymous hash The arrow operator Mutate through a ref Return a reference Code references Copy vs shared Dispatch table Refs keep lists separate Deep dereference Postfix dereference Reference identity Break a cycle with weaken

4Slices & Arrays0/18Unlock →

Reverse a list Array slice Hash slice Negative indices Ranges and slices Filter with grep grep in scalar context Assign a hash slice List slice Transform with map Numeric sort Insert with splice Remove with splice map to a hash Sort by a key Replace with splice Key/value slice Context with wantarray

5Data structures0/9Unlock →

Array basics exists and delete Hash basics keys and values Push, pop, shift, unshift Array references Hash references Array and hash slices Nested data

6Iterators0/20Unlock →

7Traits0/20Unlock →

8Generics0/20Unlock →

9Lifetimes0/20Unlock →

10Closures0/20Unlock →

11Pattern Matching0/20Unlock →

12Error Handling0/20Unlock →

13Option & Result0/20Unlock →

14Conversions0/15Unlock →

automatic conversion int truncates list to string number to string ord and chr string to list string to number binary with %b truthiness to a count hex()hex with %x sprintf precision sprintf zero-pad oct()pack and unpack

15Collection Conversions0/19Unlock →

array to a set sorted keys flat list to hash numeric sort List::Util sum List::Util uniq sorted values set difference List::Util first flatten nested refs frequency count hash to pair strings set intersection invert a hash set union unique, keep order two arrays to a hash group into buckets sort keys by value

16Math0/14Unlock →

Float functions Integer arithmetic min, max, clamp Rounding Factorial Modulo and fmod Parse number bases Logarithms and exp Mean of a list Trigonometry Greatest common divisor Primality test Median of a list Standard deviation

17Encoding0/22Unlock →

18Random0/20Unlock →

19Data I/O0/18Unlock →

Parse CSV into rows Tab-separated values Build a CSV string Select one column CSV into a number matrix Split off the header Whitespace-separated matrix Serialize records to CSV Skip blanks and comments Slurp a file, count rows Print an aligned table Write a matrix as text Structured dump with Data::Dumper Parse key=value config Round-trip write then read Tiny hand-rolled JSON decoder Tiny hand-rolled JSON encoder Drop unparseable rows

20Linear Algebra0/21Unlock →

21Text Processing0/16Unlock →

Capitalize the first letter Reverse a string Reverse word order Word count Count occurrences Number the lines Strip all whitespace Replace text Title case Count vowels Zero-pad a number Pad and align Character frequency Longest word Truncate with an ellipsis Levenshtein distance

22Date & Time0/12Unlock →

UNIX timestamp now Day of the week UTC broken-down time Seconds to HH:MM:SS Leap year Local broken-down time Date arithmetic via epoch High-resolution timing Parse a clock string Format a date with strftime Fields to epoch (UTC)Fields to epoch (local)

23Memory0/12Unlock →

Swap two values Drop a value early Replace and return the old Size of a value in bytes Take, leaving the default Mutate through a scalar ref Mutate a shared arrayref Copy versus reference Lazy static value Initialize once Reference counting Weak references break cycles

24Modules0/20Unlock →

25Macros0/20Unlock →

26Testing0/20Unlock →

27Algorithms0/8Unlock →

Greatest common divisor Binary search Palindrome check Fibonacci with memoization Fisher-Yates shuffle Merge two sorted lists Two sum Quicksort

28Sorting Algorithms0/12Unlock →

Default vs numeric sort Descending sort Bubble sort Sort by a computed key Insertion sort Selection sort Counting sort Merge sort Schwartzian transform Shell sort Heapsort Quicksort

29Expression Parsing0/6Unlock →

Evaluate postfix (RPN)Tokenize an expression Evaluate infix Recursive-descent calculator Right-associative power Shunting-yard

30Idioms0/9Unlock →

defaults with //postfix if and for chained ternary unless and until map/grep/sort chain array and hash slices context-aware return local dynamic scope Schwartzian transform

31OOP & Traits0/8Unlock →

Encapsulation Interfaces via duck typing Composition over inheritance Default methods Implementing Display Dynamic polymorphism Static polymorphism Supertraits

32Trait Objects0/14Unlock →

Return one of several types Inherited base method Take any blessed object An array of coderefs One iterator vs many Two names, one object Sum area over mixed objects Direct call vs can()Base and derived methods An array of objects Recover the concrete type Wrap a borrowed ref Require a method with can()A handler registry

33Design Patterns0/14Unlock →

Prototype Factory Method Adapter Builder Lazy Initialization Singleton Strategy Command Decorator Dependency Injection Observer Object Pool State Actor

34Async0/3Unlock →

A coderef scheduler An event loop timeout Concurrent producers

35File I/O0/6Unlock →

Read a file Write a file Append to a file Count lines Read line by line Temp file round-trip

36Filesystem0/18Unlock →

Does a path exist?Build a path Copy a file Change the extension Files vs directories Create nested directories List a directory Rename or move Path components Remove a whole tree Sorted listing File size via stat A scratch directory Absolute path Filter by extension Walk the tree Last modified time Total size of a tree

37Networking0/16Unlock →

Parse the request line Route by path Bind an ephemeral port Build an HTTP response Classify an IP address Pack a socket address Read a line from a socket Resolve a hostname Shut down a connection TCP client Read timeout UDP receive UDP send A process per connection TCP echo server Serve one HTTP request

38Concurrency0/7Unlock →

Fork a process Return data via a pipe A pipe as a channel A flock counter A worker pool Shared vs exclusive locks select() on pipes

39Unsafe & FFI0/14Unlock →

Dereference a reference A code reference A mutable global Mutate through a ref C-backed POSIX calls A by-convention contract A NUL-terminated string FFI is on CPAN Serialize to bytes Deferred initialization Values from a buffer A union in bytes vec() bit vectors Reinterpret the bits

40Commands0/14Unlock →

Command-line arguments The program name Env var with a default Read an environment variable Current directory Iterate all env vars Set and remove a variable Pass env to a child exec replaces the process Parse options with Getopt::Long Capture command output Decode the exit code Read all of stdin Run a command

41Array0/10Unlock →

Contains Duplicate Two Sum Best Time to Buy and Sell Stock Maximum Subarray Container With Most Water Find Minimum in Rotated Sorted Array Product of Array Except Self Maximum Product Subarray Search in Rotated Sorted Array 3Sum

42Binary0/5Unlock →

Missing Number Number of 1 Bits Counting Bits Reverse Bits Sum of Two Integers

43String0/10Unlock →

Valid Anagram Valid Palindrome Valid Parentheses Encode and Decode Strings Group Anagrams Longest Substring Without Repeating Characters Longest Repeating Character Replacement Longest Palindromic Substring Palindromic Substrings Minimum Window Substring

44Matrix0/4Unlock →

Rotate Image Set Matrix Zeroes Spiral Matrix Word Search

45Interval0/5Unlock →

Meeting Rooms Merge Intervals Insert Interval Non-overlapping Intervals Meeting Rooms II

46Linked List0/6Unlock →

Reverse Linked List Linked List Cycle Merge Two Sorted Lists Remove Nth Node From End Merge K Sorted Lists Reorder List

47Tree0/14Unlock →

Maximum Depth of Binary Tree Invert Binary Tree Same Tree Lowest Common Ancestor of a BST Binary Tree Level Order Traversal Subtree of Another Tree Implement Trie (Prefix Tree)Kth Smallest Element in a BST Validate Binary Search Tree Add and Search Word Construct Binary Tree from Preorder and Inorder Binary Tree Maximum Path Sum Serialize and Deserialize Binary Tree Word Search II

48Graph0/8Unlock →

Number of Connected Components Number of Islands Clone Graph Course Schedule Longest Consecutive Sequence Graph Valid Tree Alien Dictionary Pacific Atlantic Water Flow

49Heap0/3Unlock →

Kth Largest Element in an Array Top K Frequent Elements Find Median from Data Stream

50Dynamic Programming0/11Unlock →

Climbing Stairs House Robber Unique Paths Coin Change House Robber II Jump Game Combination Sum IV Decode Ways Longest Common Subsequence Longest Increasing Subsequence Word Break