Perl on JVM Feature Matrix

May 13, 2026 · View on GitHub

Status Legend

✅ Fully implemented
🚧 Partially implemented
🟡 Implemented with limitations
❌ Not implemented

Compiler Usability
Testing
Autovivification
Scalars
Objects
Operators
Arrays, Hashes, and Lists
Subroutines
Regular Expressions
Statements and Special Operators
I/O Operations
Namespaces and Global Variables
Perl Modules, Pragmas, Features
Features Incompatible with JVM
Optimizations

Summary

PerlOnJava implements most core Perl features with some key differences:

✅ Fully Supported:

Core language features (variables, loops, conditionals, subroutines)
Most operators and built-in functions
Basic OOP with packages, inheritance, and method calls
Regular expressions (most features)
DBI with JDBC integration
Subroutine prototypes
Tied variables
Method Resolution Order

🚧 Partially Supported:

Warnings and strict pragma
Some core modules and pragmas
File operations and I/O
Overload
format operator

❌ Not Supported:

XS modules and C integration
Threading

Compiler Usability

✅ Wrapper scripts: (jperl/jperl.bat) for easier command-line usage.
✅ Perl-like compile-time error messages: Error messages mimic those in Perl for consistency.
✅ Perl line numbers in bytecode: Bytecode includes line numbers for better debugging.
✅ Perl-like runtime error messages: Runtime errors are formatted similarly to Perl's.
✅ Comments: Support for comments and POD (documentation) in code is implemented.
✅ Environment: Support for PERL5LIB, PERL5OPT environment variables.
🚧 Perl-like warnings: Lexical warnings with FATAL support. Block-scoped warnings pending.

Perl Debugger

The built-in Perl debugger (perl -d) provides interactive debugging. See Debugger Reference for full documentation.

Execution Commands

Command	Status	Description
`s`	✅	Step into - execute one statement, entering subroutines
`n`	✅	Next - execute one statement, stepping over subroutines
`r`	✅	Return - execute until current subroutine returns
`c [line]`	✅	Continue - run until breakpoint or specified line
`q`	✅	Quit - exit the debugger

Breakpoints

Command	Status	Description
`b [line]`	✅	Set breakpoint at line
`b file:line`	✅	Set breakpoint at line in file
`B [line]`	✅	Delete breakpoint
`B *`	✅	Delete all breakpoints
`L`	✅	List all breakpoints
`b line condition`	❌	Conditional breakpoints

Source and Stack

Command	Status	Description
`l [range]`	✅	List source code
`.`	✅	Show current line
`T`	✅	Stack trace
`w expr`	❌	Watch expression
`a line command`	❌	Set action at line

Expression Evaluation

Command	Status	Description
`p expr`	✅	Print expression result
`x expr`	✅	Dump expression with Data::Dumper

Debug Variables

Variable	Status	Description
`$DB::single`	✅	Single-step mode flag
`$DB::trace`	✅	Trace mode flag
`$DB::signal`	✅	Signal flag
`$DB::filename`	✅	Current filename
`$DB::line`	✅	Current line number
`%DB::sub`	✅	Subroutine locations (name → file:start-end)
`@DB::args`	✅	Current subroutine arguments

Not Implemented

❌ -d:Module - Custom debugger modules (e.g., -d:NYTProf)
❌ perl5db.pl compatibility
❌ R - Restart program
❌ History and command editing

Command Line Switches

✅ Accept input program in several ways:
1. Piped input: echo 'print "Hello\n"' | ./jperl - reads from pipe and executes immediately
2. Interactive input: ./jperl - shows a prompt and waits for you to type code, then press Ctrl+D (on Unix/Linux/Mac) or Ctrl+Z (on Windows) to signal end of input
3. File redirection: ./jperl < script.pl - reads from the file
4. With arguments: ./jperl -e 'print "Hello\n"' or ./jperl script.pl
✅ UTF-16 is accepted in source code.
✅ Accept command line switches from the shebang line.
✅ Accept command line switches: -c, -e, -E, -p, -n, -i, -I, -0, -a, -d, -f, -F, -m, -M, -g, -l, -h, -s, -S, -x, -v, -V, -?, -w, -W, -X are implemented.
❌ Missing command line switches include:
- -T: Taint checks.
- -t: Taint checks with warnings.
- -u: Dumps core after compiling.
- -U: Allows unsafe operations.
- -D[number/list]: Sets debugging flags.
- -C [number/list]: Controls Unicode features.

Testing

✅ TAP tests: Running standard Perl testing protocol.
✅ CI/CD: Github testing pipeline in Ubuntu and Windows.

Autovivification

Distinguish between contexts where undefined references should automatically create data structures versus where they should throw errors.

When Autovivification Occurs:

Lvalue contexts: $arr->[0] = 'value', $hash->{key} = 'value'
Modifying operations: push @{$undef}, 'item', pop @{$undef}, shift @{$undef}, unshift @{$undef}, 'item'
Element access: $undef->[0], $undef->{key} (creates the container but not the element)
Operations that can modify through aliases: grep { $_ = uc } @{$undef}, map { $_ * 2 } @{$undef}
Foreach loops: foreach (@{$undef}) { ... }

When Autovivification Does NOT Occur, and throws error in `strict` mode:

Non-modifying operations: sort @{$undef}, reverse @{$undef}
Rvalue dereferencing: my @list = @{$undef}, my %hash = %{$undef}
Scalar context: my $count = @{$undef}

Examples:

# These autovivify (create the data structure):
my $x;
$x->[0] = 'hello';        # $x becomes []
push @{$x}, 'world';      # works, autovivifies

my $y;
$y->{name} = 'Alice';     # $y becomes {}
$y->{age}++;              # autovivifies element

# These throw "Can't use an undefined value as an ARRAY/HASH reference":
my $z;
my @sorted = sort @{$z};  # ERROR
my @reversed = reverse @{$z};  # ERROR
my @copy = @{$z};         # ERROR

Scalars

✅ my variable declaration: Local variables can be declared using my.
✅ our variable declaration: Global variables can be declared using our.
✅ local variable declaration: Dynamic variables are implemented.
✅ state variable declaration: State variables are implemented. State variables are initialized only once.
✅ Declared references: my \$x, my(\@arr), my(\%hash) are implemented.
✅ Variable assignment: Basic variable assignment is implemented.
✅ Basic types: Integers, doubles, strings, v-strings, regex, CODE, undef, and references are supported.
✅ String Interpolation: Both array and scalar string interpolation are supported.
✅ String Interpolation escapes: Handles escape sequences like \n, \N{name}, \Q, \E, \U, \L, \u, \l within interpolated strings.
✅ String numification: Strings can be converted to numbers automatically.
✅ Numbers with underscores: Numbers with underscores (e.g., 1_000) are supported.
✅ Numbers in different bases: Numbers in binary, hex, octal: 0b1010, 0xAA, 078.
✅ Infinity, -Infinity, NaN: Special number values are implemented.
✅ Hexadecimal floating point: Numbers like 0x1.999aP-4 are supported.
✅ References: References to variables and data structures are supported.
✅ Autovivification: Autovivification is implemented.
✅ File handles: Support for file handles is implemented.
✅ local special cases: local is implemented for typeglobs and filehandles.
✅ Typeglob as hash: *$val{$k} for SCALAR, ARRAY, HASH, CODE, IO is implemented.
✅ Use string as a scalar reference: Support for scalar references from strings is implemented.
✅ Tied Scalars: Support for tying scalars to classes is implemented. See also Tied Arrays, Tied Hashes, Tied Handles.
❌ Taint checks: Support for taint checks is not implemented.
❌ local special cases: local *HANDLE = *HANDLE doesn't create a new typeglob.
🚧 Variable attributes: my $x : attr supported via MODIFY_SCALAR_ATTRIBUTES etc.

Objects

✅ Objects: Creating classes and method call syntax are implemented.
✅ Object operators: ref and bless
✅ Special variables: @ISA is implemented.
✅ Multiple Inheritance: C3 method resolution is implemented.
✅ Method caching: Method resolution is cached.
✅ Version check: Method VERSION ( [ REQUIRE ] ) is implemented.
✅ Inheritance: SUPER::method is implemented.
✅ Autoload: AUTOLOAD mechanism is implemented; $AUTOLOAD variable is implemented.
✅ class: class keyword fully supported with blocks.
✅ Indirect object syntax indirect object syntax is implemented.
✅ :isa: Class inheritance with version checking is implemented.
✅ method: Method declarations with automatic $self.
✅ field: Field declarations with all sigils supported.
✅ :param: Constructor parameter fields fully working.
✅ :reader: Reader methods with context awareness.
✅ ADJUST: ADJUST blocks with field transformation work.
✅ Constructor generation: Automatic new() method creation.
✅ Field transformation: Fields become $self->{field} in methods.
✅ Lexical method calls: $self->&priv syntax is implemented.
✅ Object stringification: Shows OBJECT not HASH properly.
✅ Field defaults: Default values for fields work.
✅ Field inheritance: Parent class fields are inherited.
🟡 __CLASS__: Compile-time evaluation only, not runtime.
🟡 Argument validation: Limited by operator implementation issues.
✅ Moose / Class::MOP: Moose 2.4000 is bundled. Upstream Moose tests pass ~99%; DBIx::Class (installed via jcpan) passes 100%. See bundled modules.
✅ DESTROY: Destructor methods with selective reference counting.

Operators

Arithmetic and Comparison

✅ Simple arithmetic: Operators like +, -, *, and % are supported.
✅ Numeric Comparison operators: Comparison operators such as ==, !=, >, <, etc., are implemented.
✅ Chained operators: Operations like $x < $y <= $z are implemented.
✅ defined-or: // operator.
✅ low-precedence-xor: ^^ and ^^= operator.

String Operators

✅ String concat: Concatenation of strings using . is supported.
✅ String Comparison operators: String comparison operators such as eq, ne, lt, gt, etc., are implemented.
✅ q, qq, qw, qx String operators: Various string quoting mechanisms are supported.
✅ Scalar string and math operators: quotemeta, ref, undef, log, rand, oct, hex, ord, chr, int, sqrt, cos, sin, exp, atan2, lc, lcfirst, uc, ucfirst, chop, fc, index, rindex, prototype.
✅ join: Join operator for combining array elements into a string is supported.
✅ sprintf: String formatting is supported.
✅ substr: Substring extraction is implemented.
✅ Lvalue substr: Assignable Substring extraction is implemented.
✅ chomp: chomp is implemented.

Bitwise Operators

✅ Bitwise operators: Bitwise operations like ~, &, |, ^, ~., &., |., ^., <<, and >> are supported.
✅ Bitwise operators: Bitwise integer and string operations are implemented.
✅ Bitwise operators return unsigned: Emulate unsigned integers.
✅ Vectors: vec is implemented.
✅ Lvalue vec: Assignable vec is implemented.

List and Array Operators

✅ grep, map, sort: List processing functions are implemented.
✅ pack and unpack operators: pack and unpack are implemented.

Other Operators

✅ Autoincrement, Autodecrement; String increment: Increment and decrement operators, including for strings, are implemented.
✅ Time-related functions: time, times, gmtime, localtime are implemented.
✅ crypt operator: crypt is implemented.
✅ study, srand: study, srand are implemented.
✅ sleep: sleep is implemented. It takes fractional seconds.
✅ alarm: alarm is implemented with $SIG{ALRM} signal handling support.
✅ stat: stat, lstat are implemented. Some fields are not available in JVM and return undef.

Arrays, Hashes, and Lists

✅ Array, Hash, and List infrastructure: Basic infrastructure for arrays, hashes, and lists is implemented.
✅ List assignment: Supports list assignment like ($a, undef, @b) = @c.
✅ my LIST: Declaration of lists using my is supported.
✅ Autoquote before =>: Autoquoting before => is implemented.
✅ Select an element from a list: Indexing into lists is supported.
✅ List subscripts: like: (stat($file))[8]
✅ Taking References of a List: like: \(1,2,3)
✅ List assignment in scalar context: List assignment in scalar context returns the number of elements produced by the expression on the right side of the assignment
✅ $#array: Operator for array count is implemented.
✅ scalar: Operator to get scalar value is implemented.
✅ Array dereference: Dereferencing arrays using @$x.
✅ Hash dereference: Dereferencing hashes using %$x.
✅ **Dereference with $var{...}**: Dereferencing using `$ var{...}and$$var[...]` is implemented.
✅ Basic Array Operations: push, unshift, pop, shift, splice, reverse are implemented.
✅ Slices: Array and Hash slices like @array[2, 3], @hash{"a", "b"} and %hash{"a", "b"} are implemented.
✅ Array literals: Array literals are supported.
✅ Basic Hash Operations: keys, values, delete, exists, each are implemented.
✅ Hash literals: Hash literals are supported.
✅ List operator ..: List constructors are implemented.
✅ Flip-flop operator .. and ...: The flip-flop operators are implemented.
✅ $#array: Lvalue array count is implemented: $#{$sl} = 10.
✅ Array exists: exists for array indexes is implemented.
✅ Array delete: delete for array indexes is implemented.
✅ Tied Arrays: Tied arrays are implemented. See also Tied Scalars, Tied Hashes, Tied Handles.
✅ Tied Hashes: Tied hashes are implemented. See also Tied Scalars, Tied Arrays, Tied Handles.
❌ Restricted hashes: Hash::Util lock/unlock functions (lock_keys, lock_hash, etc.) are not implemented.

Subroutines

✅ Subroutine hoisting: Invoking subroutines before their actual declaration in the code.
✅ Anonymous subroutines with closure variables: Anonymous subs and closures are supported.
✅ Return from inside a block: Return statements within blocks work correctly.
✅ Assigning to a closure variable mutates the variable in the original context: Closure variable mutation is implemented.
✅ @_ contains aliases to the caller variables: The @_ array reflects caller arguments correctly.
✅ Named subroutines: Support for named subroutines is implemented.
✅ Calling context: wantarray is implemented.
✅ exists: exists &sub is implemented.
✅ defined: defined &sub is implemented.
✅ CORE namespace: CORE is implemented.
✅ CORE::GLOBAL namespace: CORE::GLOBAL and core function overrides are implemented.
✅ alternate subroutine call syntax: &$sub, &$sub(args) syntax is implemented.
✅ Subroutine prototypes: Prototypes $, @, %, &, ;, _, +, *, \@, \%, \$, \[@%], empty string and undef are supported.
✅ Subroutine signatures: Formal parameters are implemented.
✅ lvalue subroutines: Subroutines with attribute :lvalue are supported.
✅ Forcing main package: Identifiers starting with :: are in main package.
✅ Lexical subroutines: Subroutines declared my, state, or our are supported.
🚧 Subroutine attributes: :lvalue, :prototype, and custom attributes via MODIFY_CODE_ATTRIBUTES/FETCH_CODE_ATTRIBUTES.
✅ CORE operator references: \&CORE::X returns callable CODE refs for built-in functions with correct prototypes: my $r = \&CORE::length; $r->("hello")

Regular Expressions

✅ Basic Matching: Operators qr//, m//, s///, split are implemented.
✅ Regex modifiers: Modifiers /p /i /m /s /n /g /c /r /e /ee /x /xx are implemented.
✅ Special variables: The special variables $1, $2... are implemented.
✅ Transliteration: tr and y transliteration operators are implemented.
✅ pos: pos operator is implemented.
✅ \G: \G operator in regex is implemented.
✅ \N{name}: \N{name} and \N{U+hex} operator for named characters in regex is implemented.
✅ \N: Not-newline operator.
✅ lvalue pos: lvalue pos operator is implemented.
✅ m?pat? one-time match is implemented.
✅ reset resetting one-time match is implemented
✅ @-, @+, %+, %-, @{^CAPTURE}, ${^LAST_SUCCESSFUL_PATTERN} variables: regex special variables are implemented
✅ $& variables: $`, $&, $', $+ special variables are implemented, and aliases: ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH}.
✅ [[:pattern:]]: [[:ascii:]], [[:print:]] are implemented.
✅ Matching plain strings: $var =~ "Test" is implemented.
✅ Inline comments: (?#comment) in regex is implemented.
✅ caret modifier: (?^ embedded pattern-match modifier, shorthand equivalent to "d-imnsx".
✅ \b inside character class: [\b] is supported in regex.
✅ \b{gcb} \B{gcb}: Boundary assertions.
✅ Variable Interpolation in Regex: Features like ${var} for embedding variables.
✅ Non-capturing groups: (?:...) is implemented.
✅ Named Capture Groups: Defining named capture groups using (?<name>...) or (?'name'...) is supported.
✅ Backreferences to Named Groups: Using \k<name> or \g{name} for backreferences to named groups is supported.
✅ Relative Backreferences: Using \g{-n} for relative backreferences.
✅ Unicode Properties: Matching with \p{...} and \P{...} (e.g., \p{L} for letters).
✅ Unicode Properties: Add regex properties supported by Perl but missing in Java regex.
✅ Possessive Quantifiers: Quantifiers like *+, ++, ?+, or {n,m}+, which disable backtracking, are not supported.
✅ Atomic Grouping: Use of (?>...) for atomic groups is supported.
✅ \K assertion: Keep left — in s///, text before \K is preserved; match variables reflect only the portion after \K.
✅ Preprocessor: \Q, \L, \U, \l, \u, \E are preprocessed in regex.
✅ Overloading: qr overloading is implemented. See also overload pragma.

Missing Regular Expression Features

❌ Dynamically-scoped regex variables: Regex variables are not dynamically-scoped.
❌ Recursive Patterns: Features like (?R), (?0) or (??{ code }) for recursive matching are not supported.
❌ Backtracking Control: Features like (?>...), (?(DEFINE)...), or (?>.*) to prevent or control backtracking are not supported.
❌ Lookbehind Assertions: Variable-length negative or positive lookbehind assertions, e.g., (?<=...) or (?<!...), are not supported.
❌ Branch Reset Groups: Use of (?|...) to reset group numbering across branches is not supported.
❌ Advanced Subroutine Calls: Sub-pattern calls with numbered or named references like (?1), (?&name) are not supported.
❌ Conditional Expressions: Use of (?(condition)yes|no) for conditional matching is not supported.
❌ Extended Unicode Regex Features: Some extended Unicode regex functionalities are not supported.
❌ Extended Grapheme Clusters: Matching with \X for extended grapheme clusters is not supported.
❌ Embedded Code in Regex: Inline Perl code execution with (?{ code }) or (??{ code }) is not supported.
❌ Regex Debugging: Debugging patterns with use re 'debug'; to inspect regex engine operations is not supported.
❌ Regex Optimizations: Using use re 'eval'; for runtime regex compilation is not supported.
❌ Regex Compilation Flags: Setting default regex flags with use re '/flags'; is not supported.
❌ Stricter named captures
- ❌ No underscore in named captures (?<test_field>test) the name in named captures cannot have underscores.
- ❌ No duplicate named capture groups: In Java regular expression engine, each named capturing group must have a unique name within a regular expression.

Statements and Special Operators

✅ Context void, scalar, list: Contexts for void, scalar, and list are supported.
✅ if/else/elsif and unless: Conditional statements are implemented.
✅ 3-argument for loop: The for loop with three arguments is supported.
✅ foreach loop: The foreach loop is implemented.
✅ while and until loop: while and until loops are supported.
✅ if unless Statement modifiers: Conditional modifiers for if and unless are implemented.
✅ while until Statement modifiers: Loop modifiers for while and until are supported.
✅ while until Statement modifiers: last, redo, next give an error Can't "last" outside a loop block.
✅ for foreach Statement modifiers: Loop modifiers for for and foreach are implemented.
✅ continue blocks: continue blocks in looks are implemented.
✅ try/catch try-catch is supported.
✅ eval string with closure variables: eval in string context with closures is supported.
✅ eval string sets $@ on error; returns undef: eval sets $@ on error and returns undef.
✅ eval block: eval blocks are implemented.
✅ do block: do blocks are supported.
✅ do file: File execution using do is implemented.
✅ do \&subroutine: is implemented.
✅ print operators: print, printf and say statements are implemented, with support for file handles.
✅ printf and sprintf: String formatting is implemented.
✅ Short-circuit and, or: Short-circuit logical operators are supported.
✅ Low-precedence/high precedence operators: Logical operators like not, or, and, xor are supported.
✅ Ternary operator: The ternary conditional operator is implemented.
✅ Compound assignment operators: Compound assignment operators are implemented.
✅ package declaration: package BLOCK is also supported.
✅ Typeglob operations: Operations like *x = sub {}, *x = \@a, *x = *y are supported.
✅ Code references: Code references like \&subr, \&$subname, \&{$subname}, are implemented.
✅ Special literals: __PACKAGE__, __FILE__, __LINE__
✅ die, warn operators: die, warn are supported.
✅ die related features: $SIG{__DIE__}, $SIG{__WARN__}
✅ die with object: PROPAGATE method is supported.
✅ exit: exit is supported.
✅ kill: kill is supported.
✅ waitpid: waitpid is partially supported.
✅ utime: utime is supported.
✅ umask: umask is supported.
✅ chown: chown is supported.
✅ readlink: readlink is supported.
✅ link, symlink: link is supported.
✅ rename: rename is supported.
✅ require operator: The require operator implemented; version checks are implemented.
✅ require operator: pmc files are supported.
✅ use and no statements: Module imports and version check via use and no are implemented; version checks are implemented. use arguments are executed at compile-time.
✅ use version: use version enables the corresponding features, strictures, and warnings.
✅ Import methods: import and unimport are implemented.
✅ __SUB__: The __SUB__ keyword is implemented.
✅ BEGIN block: BEGIN special block is implemented.
✅ END block: END special block is implemented.
✅ INIT: special block is implemented.
✅ CHECK: special block is implemented.
✅ UNITCHECK: special block is implemented.
✅ Labels: Labels are implemented.
✅ Here-docs: Here-docs for multiline string literals are implemented.
✅ Preprocessor: # line directive is implemented.
✅ glob: glob operator is implemented.
✅ <>: <> operator is implemented.
✅ <$fh>: <$fh> and <STDIN> operators are implemented.
✅ <ARGV>: ARGV and $ARGV are implemented.
✅ <*.*>: <*.*> glob operator is implemented.
✅ End of file markers: Source code control characters ^D and ^Z, and the tokens __END__ and __DATA__ are implemented.
❌ Startup processing: processing $sitelib/sitecustomize.pl at startup is not enabled.
❌ Smartmatch operator: ~~ and given/when construct are not implemented.
✅ File test operators: -R, -W, -X, -O (for real uid/gid), this implementation assumes that the real user ID corresponds to the current user running the Java application.
✅ File test operators: -t (tty check), this implementation assumes that the -t check is intended to determine if the program is running in a TTY-compatible environment.
✅ File test operators: -p, -S, -b, and -c are approximated using file names or paths, as Java doesn't provide direct equivalents.
✅ File test operators: -k (sticky bit) is approximated using the "others execute" permission, as Java doesn't have a direct equivalent.
✅ File test operators: -T and -B (text/binary check) are implemented using a heuristic similar to Perl's approach.
✅ File test operators: Time-based operators (-M, -A, -C) return the difference in days as a floating-point number.
✅ File test operators: Using _ as the argument reuses the last stat result.
✅ File test operators: Support stacked file test operators.
✅ Directory operators: readdir, opendir, closedir, telldir, seekdir, rewinddir, mkdir, rmdir, chdir.
✅ for loop variable: The for loop variable is aliased to list elements.
✅ for loop variable: Iterate over multiple values at a time is implemented.
✅ for loop variable: You can use fully qualified global variables as the variable in a for loop.
✅ loop control operators: next LABEL, last LABEL, redo LABEL with literal labels are implemented, including non-local control flow (jumping from subroutines to caller's loops).
✅ goto operator: goto LABEL with literal labels and goto EXPR with dynamic expressions are implemented.
✅ goto &name: Tail call optimization with trampoline is implemented.
✅ goto __SUB__: Recursive tail call is implemented.
✅ loop control operators: next EXPR, last EXPR, redo EXPR with dynamic expressions (e.g., $label = "OUTER"; next $label) are implemented.
✅ setting $_ in while loop with <>: automatic setting $_ in while loops is implemented.
✅ do BLOCK while: do executes once before the conditional is evaluated.
✅ ... ellipsis statement: ... is supported.
✅ system operator: system is implemented.
✅ exec operator: exec is implemented.
✅ User/Group operators, Network info operators: getlogin, getpwnam, getpwuid, getgrnam, getgrgid, getpwent, getgrent, setpwent, setgrent, endpwent, endgrent, gethostbyname, gethostbyaddr, getservbyname, getservbyport, getprotobyname, getprotobynumber.
✅ Network enumeration operators: endhostent, endnetent, endprotoent, endservent, gethostent, getnetbyaddr, getnetbyname, getnetent, getprotoent, getservent, sethostent, setnetent, setprotoent, setservent.
✅ System V IPC operators: msgctl, msgget, msgrcv, msgsnd, semctl, semget, semop, shmctl, shmget, shmread, shmwrite.
✅ format operator: format and write functions for report generation are implemented.
✅ formline operator: formline and $^A accumulator variable are implemented.

I/O Operations

Basic I/O Operators

✅ open: File opening is implemented with support for:
- 2-argument forms: <-, -, >-, filename
- 3-argument forms with explicit modes
- In-memory files
- support for pipe input and output like: -|, |-, ls|, |sort.
  - forking patterns with exec:
    my $pid = open FH, "-|"; if ($ pid) {...} else { exec @cmd } my $pid = open FH, "-|"; unless ($ pid) { exec @cmd } ... open FH, "-|" or exec @cmd;
- ✅ file descriptor duplication modes: <&, >&, <&=, >&= (duplicate existing file descriptors)
✅ readline: Reading lines from filehandles
- ✅ Paragraph mode ($/ = '' - empty string)
- ✅ Record length mode ( $/ = \2,$ / = $foo where $foo is a number)
- ✅ Slurp mode ($/ = undef)
- ✅ Multi-character string separators ($/ = "34")
✅ sysopen: File opening.
✅ eof: End-of-file detection
✅ close: Closing filehandles
✅ unlink: File deletion
✅ readpipe: Command output capture
✅ fileno: File descriptor retrieval
✅ getc: Character reading
✅ read: Block reading with length specification
✅ tell: Current file position
✅ select: select(filehandle) for default output selection
✅ select: select(undef,undef,undef,$time) for sleep function
✅ seek: File position manipulation.
✅ chmod: File permissions.
✅ sysread
✅ syswrite
✅ Tied Handles: Tied file handles are implemented. See also Tied Scalars, Tied Arrays, Tied Hashes.
✅ DATA: DATA file handle is implemented.
✅ truncate: File truncation
✅ flock: File locking with LOCK_SH, LOCK_EX, LOCK_UN, LOCK_NB
✅ fcntl: File control operations (stub + native via jnr-posix)
✅ ioctl: Device control operations (stub + native via jnr-posix)
✅ syscall: System calls (SYS_gethostname)

Socket Operations

✅ socket: Socket creation with domain, type, and protocol support
✅ bind: Socket binding to addresses
✅ listen: Socket listening for connections
✅ accept: Connection acceptance
✅ connect: Socket connection establishment
✅ send: Data transmission over sockets
✅ recv: Data reception from sockets
✅ shutdown: Socket shutdown
✅ setsockopt: Socket option configuration
✅ getsockopt: Socket option retrieval
✅ getsockname: Local socket address retrieval
✅ getpeername: Remote socket address retrieval
✅ socketpair: Connected socket pair creation
✅ pipe: Internal pipe creation for inter-process communication

Unimplemented I/O Operators

I/O Layers

✅ Layer support: open and binmode support these I/O layers:
- :raw - Binary mode, no translation
- :bytes - Similar to :raw, ensures byte semantics
- :crlf - Convert CRLF to LF on input, LF to CRLF on output
- :utf8 - UTF-8 encoding/decoding
- :unix - Unix-style line endings (LF only)
- :encoding(ENCODING) - Specific character encoding
✅ Layer stacking: Multiple layers can be combined (e.g., :raw:utf8)
❌ Multibyte encoding support for seek, tell, truncate: These operations are not yet implemented for multibyte encodings.

Supported Encodings

The :encoding() layer supports all encodings provided by Java's Charset.forName() method:

Standard Charsets (guaranteed available):

US-ASCII - Seven-bit ASCII
ISO-8859-1 - ISO Latin Alphabet No. 1 (Latin-1)
UTF-8 - Eight-bit UCS Transformation Format
UTF-16BE - Sixteen-bit UCS, big-endian byte order
UTF-16LE - Sixteen-bit UCS, little-endian byte order
UTF-16 - Sixteen-bit UCS with optional byte-order mark

Common Extended Charsets (usually available):

windows-1252 - Windows Western European
ISO-8859-2 through ISO-8859-16 - Various ISO Latin alphabets
Shift_JIS - Japanese
EUC-JP - Japanese
GB2312, GBK, GB18030 - Chinese
Big5 - Traditional Chinese
EUC-KR - Korean
windows-1251 - Windows Cyrillic
KOI8-R - Russian

Namespaces and Global Variables

✅ Global variable infrastructure: Support for global variables is implemented.
✅ Namespaces: Namespace support is implemented.
✅ Stash: Stash can be accessed as a hash, like: $namespace::{entry}.
✅ @_ and $@ special variables: Special variables like @_ and $@ are supported.
✅ Special variables: The special variables %ENV, @ARGV, @INC, $0, $_, $., $], $", $\\, $,, $/, $$, $a, $b, $^O, $^V, $^X are implemented.
✅ I/O symbols: STDOUT, STDERR, STDIN, ARGV, ARGVOUT are implemented.
✅ Stash manipulation: Alternative ways to create constants like: $constant::{_CAN_PCS} = \$const.
✅ reset("A-Z") resetting global variables is implemented.
✅ Single-quote as package separator: Legacy $a'b style package separator is supported.
❌ Thread-safe @_, $_, and regex variables: Thread safety for global special variables is missing.
❌ Compiler flags: The special variables $^H, %^H, ${^WARNING_BITS} are not implemented.
✅ caller operator: caller returns ($package, $filename, $line).
- ❌ Extended call stack information: extra debug information like (caller($level))[9] is not implemented.
  This means we don't include subroutine names in error messages yet.
  Extra debug information: ($package, $filename, $line, $subroutine, $hasargs, $wantarray, $evaltext, $is_require, $hints, $bitmask, $hinthash)

Perl Modules, Pragmas, Features

❌ No direct Perl-to-Java interoperability: PerlOnJava does not provide Perl-side mechanisms like Inline::Java for directly calling Java methods or instantiating Java objects from Perl code. You cannot write Perl code that directly accesses arbitrary Java libraries or JVM languages.
✅ Java-implemented Perl modules via XSLoader: However, Perl modules can load Java-implemented subroutines using the standard XSLoader mechanism. This allows you to:
- Write Perl module implementations in Java that expose a Perl API
- Use PerlOnJava's internal API to create Java classes that register themselves as Perl subroutines
- Load these Java implementations transparently from Perl code using XSLoader
Example: The DBI module demonstrates this pattern:
- DBI.pm - Standard Perl module that uses XSLoader::load('DBI')
- DBI.java - Java implementation that registers methods like connect, prepare, execute as Perl subroutines
- From Perl's perspective, it's using a normal XS module, but the implementation is actually Java code
See XS Compatibility for a complete list of modules with Java implementations.

Pragmas

🚧 strict pragma:.
- ✅ all use strict modes are implemented.
- ✅ no strict vars, no strict subs are implemented.
- 🚧 no strict refs is partially implemented: scalar, glob references.
- ❌ no strict refs works with global variables only. my variables can not be accessed by name.
✅ parent pragma
✅ base pragma
✅ constant pragma
✅ experimental pragma
✅ if pragma
✅ lib pragma
✅ mro (Method Resolution Order) pragma
✅ vars pragma
✅ version pragma
✅ subs pragma
🚧 utf8 pragma: utf8 is always on. Disabling utf8 might work in a future version.
🚧 bytes pragma
🚧 feature pragma
- ✅ Features implemented: fc, say, current_sub, isa, state, try, defer, bitwise, postderef, evalbytes, module_true, signatures, class, keyword_all, keyword_any.
- ❌ Features missing: postderef_qq, unicode_eval, unicode_strings, refaliasing.
🚧 warnings pragma
🚧 attributes pragma: MODIFY_*_ATTRIBUTES/FETCH_*_ATTRIBUTES callbacks for subroutines and variables.
❌ bignum, bigint, and bigrat pragmas
❌ encoding pragma
❌ integer pragma
❌ locale pragma
❌ ops pragma
🚧 re pragma for regular expression options: Implemented is_regexp.
🚧 vmsish pragma.
✅ subs pragma.
🚧 builtin pragma:
- ✅ Implemented: true false is_bool inf nan weaken unweaken is_weak blessed refaddr reftype created_as_string created_as_number stringify ceil floor indexed trim is_tainted.
- ❌ Missing: export_lexically, load_module
🚧 overload pragma:
- ✅ Implemented: "", 0+, bool, fallback, nomethod.
- ✅ Implemented: !, +, -, *, /, %, int, neg, log, sqrt, cos, sin, exp, abs, atan2, **.
- ✅ Implemented: @{}, %{}, ${}, &{}, *{}.
- ✅ Implemented: <=>, cmp, <, <=, >, >=, ==, !=, lt, le, gt, ge, eq, ne.
- ✅ Implemented: qr.
- ✅ Implemented: +=, -=, *=, /=, %=.
- ✅ Implemented: <>.
- ❌ Missing: ++, --, =.
- ❌ Missing: &, |, ^, ~, <<, >>, &., |., ^., ~., x, ..
- ❌ Missing: **=, <<=, >>=, x=, .=, &=, |=, ^=, &.=, |.=, ^.=.
- ❌ Missing: -X.
- ❌ Missing: = copy constructor for mutators.
❌ overloading pragma

Core modules

✅ Benchmark use the same version as Perl.
✅ Carp: carp, cluck, croak, confess, longmess, shortmess are implemented.
✅ Config module.
✅ Cwd module
✅ Data::Dumper: use the same version as Perl.
✅ DirHandle module.
✅ Dumpvalue module.
✅ Digest module
✅ Digest::MD5 module
✅ Digest::SHA module
✅ Encode module.
✅ Env module
✅ Errno module.
✅ Exporter: @EXPORT_OK, @EXPORT, %EXPORT_TAGS are implemented.
- ❌ Missing: export *glob.
✅ ExtUtils::MakeMaker module: PerlOnJava version installs pure Perl modules directly.
✅ Fcntl module
✅ FileHandle module
✅ Filter::Simple module: FILTER and FILTER_ONLY for source code filtering.
✅ File::Basename use the same version as Perl.
✅ File::Find use the same version as Perl.
✅ File::Spec::Functions module.
✅ File::Spec module.
✅ Getopt::Long module.
✅ HTTP::Date module.
✅ Internals: Internals::SvREADONLY is implemented as a no-op.
✅ IO::File module.
✅ IO::Seekable module.
✅ IO::Socket module.
✅ IO::Socket::INET module.
✅ IO::Socket::UNIX module.
✅ IO::Zlib module.
✅ List::Util: module.
✅ MIME::Base64 module
✅ MIME::QuotedPrint module
✅ Perl::OSType module.
✅ Scalar::Util: blessed, reftype, set_prototype, dualvar are implemented.
✅ SelectSaver: module.
✅ Storable: module. Reads and writes the native Perl Storable binary format (pst0 magic), interoperable with system perl in both directions: jperl-written files are readable by system perl and vice versa. $Storable::canonical, SX_REGEXP/SX_VSTRING encoding, and full STORABLE_freeze hook emission are not yet implemented (see dev/modules/storable_binary_format.md).
✅ Sys::Hostname module.
✅ Symbol: gensym, qualify and qualify_to_ref are implemented.
✅ Term::ANSIColor module.
✅ Test module.
✅ Test::More module.
✅ Text::Balanced use the same version as Perl.
✅ Tie::Array module.
✅ Tie::Handle module.
✅ Tie::Hash module.
✅ Tie::Scalar module.
✅ Time::HiRes module.
✅ Time::Local module.
✅ UNIVERSAL: isa, can, DOES, VERSION are implemented. isa operator is implemented.
✅ URI::Escape module.
✅ Socket module: socket constants and functions (pack_sockaddr_in, unpack_sockaddr_in, sockaddr_in, inet_aton, inet_ntoa, gethostbyname).
✅ Unicode::UCD module.
✅ XSLoader module.
🚧 DynaLoader placeholder module.
🚧 HTTP::Tiny some features untested: proxy settings.
🚧 POSIX module.
🚧 Unicode::Normalize normalize, NFC, NFD, NFKC, NFKD.
✅ Archive::Tar module.
✅ Archive::Zip module.
✅ IPC::Open2 module.
✅ IPC::Open3 module.
✅ Net::FTP module.
✅ Net::Cmd module.
❌ Safe module.

Non-core modules

✅ HTTP::CookieJar module.
✅ JSON module.
✅ Cpanel::JSON::XS module (JSON::PP-backed shim; same bundled encoder/decoder stack as JSON).
✅ Text::CSV module.
✅ TOML module.
✅ XML::Parser module backed by JDK SAX (replaces native libexpat XS).
✅ YAML::PP module.
✅ YAML module.
✅ IO::Socket::SSL module backed by Java javax.net.ssl SSLEngine.
✅ Net::SSLeay module backed by Java security APIs (2327 CPAN tests pass).
✅ Plack::Handler::Netty PSGI web server with HTTP/HTTPS, streaming, 32k+ req/sec. See Web Server Guide.

DBI module

JDBC Integration

The DBI module provides seamless integration with JDBC drivers:

Configure JDBC drivers: See Adding JDBC Drivers
Connect to databases: See Database Connection Examples

Implemented Methods

connect, prepare, execute
fetchrow_arrayref, fetchrow_array, fetchrow_hashref, selectrow_array, selectrow_arrayref, selectrow_hashref
fetchall_arrayref, selectall_arrayref, fetchall_hashref, selectall_hashref
rows, disconnect, err, errstr, state, do, finish, last_insert_id
begin_work, commit, rollback
bind_param, bind_param_inout, bind_col, bind_columns
table_info, column_info, primary_key_info, foreign_key_info, type_info
clone, ping, trace, trace_msg
available_drivers, data_sources, get_info
prepare_cached, connect_cached

Database Handle Attributes

RaiseError, PrintError, Username, Password, Name, Active, Type, ReadOnly, Executed, AutoCommit

Statement Handle Attributes

NAME, NAME_lc, NAME_uc, NUM_OF_FIELDS, NUM_OF_PARAMS, Database

Features Incompatible with JVM

❌ fork operator: fork is not implemented. Calling fork will always fail and return undef.
✅ DESTROY: Implemented with selective reference counting on top of JVM GC. Supports cascading destruction, closure capture tracking, weaken/isweak/unweaken, global destruction phase, and Internals::SvREFCNT introspection.
❌ Perl XS code: XS code interfacing with C is not supported on the JVM.
❌ Auto-close files: File auto-close depends on handling of object destruction, may be incompatible with JVM garbage collection. All files are closed before the program ends.
❌ Keywords related to the control flow of the Perl program: dump operator.
❌ DBM file support: dbmclose, dbmopen are not implemented.
❌ Calling a class name package Test; Test->() gives Undefined subroutine &Test::Test called.

Optimizations

✅ Cached string/numeric conversions: Numification caching is implemented.
✅ Java segment size limitation: A workaround is implemented to Java 64k bytes segment limit.
❌ Inline "constant" subroutines optimization: Optimization for inline constants is not yet implemented.
❌ Overload optimization: Preprocessing in overload should be cached.
❌ I/O optimization: Use low-level readline to optimize input.
❌ I/O optimization: Extract I/O buffering code (StandardIO.java) into a new layer, and add it at the top before other layers.