Perinci::CmdLine - Rinci/Riap-based command-line application framework


version 1.08


In your command-line script:

 use 5.010;
 use Log::Any '$log';
 use Perinci::CmdLine 1.04;

 our %SPEC;
 $SPEC{foo} = {
     v => 1.1,
     summary => 'Does foo to your computer',
     args => {
         bar => {
             schema=>['str*', {in=>[qw/aa bb cc/]}],
         baz => {
 sub foo {
     my %args = @_;
     $log->debugf("Arguments are %s", \%args);
     [200, "OK", $args{bar} . ($args{baz} ? "and $args{baz}" : "")];

 Perinci::CmdLine->new(url => '/main/foo')->run;

To run this program:

 % foo --help ;# display help message
 % LANG=id_ID foo --help ;# display help message in Indonesian
 % foo --version ;# display version
 % foo --bar aa ;# run function and display the result
 % foo --bar aa --debug ;# turn on debug output
 % foo --baz x  ;# fail because required argument 'bar' not specified

To do bash tab completion:

 % complete -C foo foo ;# can be put in ~/.bashrc
 % foo <tab> ;# completes to --help, --version, --bar, --baz and others
 % foo --b<tab> ;# completes to --bar and --baz
 % foo --bar <tab> ;# completes to aa, bb, cc

See also the peri-run script which provides a command-line interface for Perinci::CmdLine.


Perinci::CmdLine is a command-line application framework. It parses command-line options and dispatches to one of your specified Perl functions, passing the command-line options and arguments to the function. It accesses functions via Riap protocol (using the Perinci::Access Riap client library) so you can access remote functions transparently. It utilizes Rinci metadata in the code so the amount of plumbing that you have to do is quite minimal. Basically most of the time you just need to write your "business logic" in your function (along with some metadata), and with a couple or several lines of script you have created a command-line interface with the following features:

  • Command-line options parsing

    Non-scalar arguments (array, hash, other nested) can also be passed as JSON or YAML. For example, if the tags argument is defined as 'array', then all of below are equivalent:

     % mycmd --tags-yaml '[foo, bar, baz]'
     % mycmd --tags-yaml '["foo","bar","baz"]'
     % mycmd --tags foo --tags bar --tags baz
  • Help message (utilizing information from metadata, supports translation)

     % mycmd --help
     % mycmd -h
     % mycmd -?
  • Tab completion for bash (including completion from remote code)

     % complete -C mycmd mycmd
     % mycmd --he<tab> ; # --help
     % mycmd s<tab>    ; # sub1, sub2, sub3 (if those are the specified subcommands)
     % mycmd sub1 -<tab> ; # list the options available for sub1 subcommand

    Support for other shell might be added in the future upon request.

  • Undo/redo/history

    If the function supports transaction (see Rinci::Transaction, Riap::Transaction) the framework will setup transaction and provide command to do undo (--undo) and redo (--redo) as well as seeing the undo/transaction list (--history) and clearing the list (--clear-history).

  • Version (--version, -v)

  • List available subcommands (--subcommands)

  • Configurable output format (--format, --format-options)

    By default yaml, json, text, text-simple, text-pretty are recognized.

Note that the each of the above command-line options (--help, --version, etc) can be renamed or disabled.

This module uses Log::Any and Log::Any::App for logging. This module uses Moo for OO.


Below is the description of how the framework determines what action and which function to call. (Currently lots of internal attributes are accessed directly, this might be rectified in the future.)

Actions. The _actions attribute is an array which contains the list of potential actions to choose, in order. It will then be filled out according to the command-line options specified. For example, if --help is specified, help action is shifted to the beginning of _actions. Likewise for --subcommands, etc. Finally, the call action (which means an action to call our function) is added to this list. After we are finished filling out the _actions array, the first action is chosen by running a method called run_<ACTION>. For example if the chosen action is help, run_help() is called. These run_* methods must execute the action, display the output, and return an exit code. Program will end with this exit code. A run_* method can choose to decline handling the action by returning undef, in which case the next action will be tried, and so on until a defined exit code is returned.

The 'call' action and determining which subcommand (function) to call. The call action (implemented by run_call()) is the one that actually does the real job, calling the function and displaying its result. The _subcommand attribute stores information on the subcommand to run, including its Riap URL. If there are subcommands, e.g.:

 my $cmd = Perinci::CmdLine->new(
     subcommands => {
         sub1 => {
             url => '/MyApp/func1',
         sub2 => {
             url => '/MyApp/func2',

then which subcommand to run is determined by the command-line argument, e.g.:

 % myapp sub1 ...

then _subcommand attribute will contain {url=>'/MyApp/func1'}. When no subcommand is specified on the command line, run_call() will decline handling the action and returning undef, and the next action e.g. help will be executed. But if default_subcommand attribute is set, run_call() will run the default subcommand instead.

When there are no subcommands, e.g.:

 my $cmd = Perinci::CmdLine->new(url => '/MyApp/func');

_subcommand will simply contain {url=>'/MyApp/func'}.

run_call() will call the function specified in the url in the _subcommand using Perinci::Access. (Actually, run_help() or run_completion() can be called instead, depending on which action to run.)


Logging is done with Log::Any (for producing) and Log::Any::App (for displaying to outputs). Loading Log::Any::App will add to startup overhead time, so this module tries to be smart when determining whether or not to do logging output (i.e. whether or not to load Log::Any::App). Here are the order of rules being used:

  • If running shell completion (COMP_LINE is defined), output is off

    Normally, shell completion does not need to show log output.

  • If LOG environment is defined, use that

    You can make a command-line program start a bit faster if you use LOG=0.

  • If subcommand's log_any_app setting is defined, use that

    This allows you, e.g. to turn off logging by default for subcommands that need faster startup time. You can still turn on logging for those subcommands by LOG=1.

  • If action metadata's default_log setting is defined, use that

    For example, actions like help, list, and version has default_log set to 0, for faster startup time. You can still turn on logging for those actions by LOG=1.

  • Use log_any_app attribute setting


By default, binmode(STDOUT, ":utf8") is issued if utf8 output is desired. This is determined by, in order:

  • Use setting from environment UTF8, if defined.

    This allows you to force-disable or force-enable utf8 output.

  • Use setting from action metadata, if defined.

    Some actions like help, list, and version output translated text, so they have their use_utf8 metadata set to 1.

  • Use setting from subcommand, if defined.

  • Use setting from use_utf8 attribute.

    This attribute comes from SHARYANTO::Role::TermAttrs, its default is determined from UTF8 environment as well as terminal's capabilities.


By default colors are used, but if terminal is detected as not having color support, they are turned off. You can also turn off colors by setting COLOR=0 or using PERINCI_CMDLINE_COLOR_THEME=Default::no_color.


This section describes how Perinci::CmdLine parses command-line options/arguments into function arguments. Command-line option parsing is implemented by Perinci::Sub::GetArgs::Argv.

For boolean function arguments, use --arg to set arg to true (1), and --noarg to set arg to false (0). A flag argument ([bool => {is=>1}]) only recognizes --arg and not --noarg. For single letter arguments, only -X is recognized, not --X nor --noX.

For string and number function arguments, use --arg VALUE or --arg=VALUE (or -X VALUE for single letter arguments) to set argument value. Other scalar arguments use the same way, except that some parsing will be done (e.g. for date type, --arg 1343920342 or --arg '2012-07-31' can be used to set a date value, which will be a DateTime object.) (Note that date parsing will be done by Data::Sah and currently not implemented yet.)

For arguments with type array of scalar, a series of --arg VALUE is accepted, a la Getopt::Long:

 --tags tag1 --tags tag2 ; # will result in tags => ['tag1', 'tag2']

For other non-scalar arguments, also use --arg VALUE or --arg=VALUE, but VALUE will be attempted to be parsed using JSON, and then YAML. This is convenient for common cases:

 --aoa  '[[1],[2],[3]]'  # parsed as JSON
 --hash '{a: 1, b: 2}'   # parsed as YAML

For explicit JSON parsing, all arguments can also be set via --ARG-json. This can be used to input undefined value in scalars, or setting array value without using repetitive --arg VALUE:

 --str-json 'null'    # set undef value
 --ary-json '[1,2,3]' # set array value without doing --ary 1 --ary 2 --ary 3
 --ary-json '[]'      # set empty array value

Likewise for explicit YAML parsing:

 --str-yaml '~'       # set undef value
 --ary-yaml '[a, b]'  # set array value without doing --ary a --ary b
 --ary-yaml '[]'      # set empty array value


To do bash completion, first create your script, e.g. myscript, that uses Perinci::CmdLine:

 use Perinci::CmdLine;

then execute this in bash (or put it in bash startup files like /etc/bash.bashrc or ~/.bashrc for future sessions):

 % complete -C myscript myscript; # myscript must be in PATH


For functions that express that they do progress updating (by setting their progress feature to true), Perinci::CmdLine will setup an output, currently either Progress::Any::Output::TermProgressBar if program runs interactively, or Progress::Any::Output::LogAny if program doesn't run interactively.


program_name => STR (default from $0)

use_utf8 => BOOL

From SHARYANTO::Role::TermAttrs (please see its docs for more details). There are several other attributes added by the role.

url => STR

Required if you only want to run one function. URL should point to a function entity.

Alternatively you can provide multiple functions from which the user can select using the first argument (see subcommands).

summary => STR

If unset, will be retrieved from function metadata when needed.

action_metadata => HASH

Contains a list of known actions and their metadata. Keys should be action names, values should be metadata. Metadata is a hash containing these keys:

  • default_log => BOOL (optional)

    Whether to enable logging by default (Log::Any::App) when LOG environment variable is not set. To speed up program startup, logging is by default turned off for simple actions like help, list, version.

  • use_utf8 => BOOL (optional)

    Whether to issue binmode(STDOUT, ":utf8"). See "UTF8 OUTPUT" for more details.

subcommands => {NAME => {ARGUMENT=>...}, ...} | CODEREF

Should be a hash of subcommand specifications or a coderef.

Each subcommand specification is also a hash(ref) and should contain these keys:

  • url (str, required)

    Location of function (accessed via Riap).

  • summary (str, optional)

    Will be retrieved from function metadata at url if unset

  • description (str, optional)

    Shown in verbose help message, if description from function metadata is unset.

  • tags (array of str, optional)

    For grouping or categorizing subcommands, e.g. when displaying list of subcommands.

  • log_any_app (bool, optional)

    Whether to load Log::Any::App, default is true. For subcommands that need fast startup you can try turning this off for said subcommands. See "LOGGING" for more details.

  • use_utf8 (bool, optional)

    Whether to issue "binmode(STDOUT, ":utf8")". See "LOGGING" for more details.

  • undo (bool, optional)

    Can be set to 0 to disable transaction for this subcommand; this is only relevant when undo attribute is set to true.

  • show_in_help (bool, optional, default 1)

    If you have lots of subcommands, and want to show only some of them in --help message, set this to 0 for subcommands that you do not want to show.

  • pass_cmdline_object (bool, optional, default 0)

    To override pass_cmdline_object attribute on a per-subcommand basis.

  • args (hash, optional)

    If specified, will send the arguments (as well as arguments specified via the command-line). This can be useful for a function that serves more than one subcommand, e.g.:

     subcommands => {
         sub1 => {
             summary => 'Subcommand one',
             url     => '/some/func',
             args    => {flag=>'one'},
         sub2 => {
             summary => 'Subcommand two',
             url     => '/some/func',
             args    => {flag=>'two'},

    In the example above, both subcommand sub1 and sub2 point to function at /some/func. But the function can differentiate between the two via the flag argument being sent.

     % cmdprog sub1 --foo 1 --bar 2
     % cmdprog sub2 --foo 2

    In the first invocation, function will receive arguments {foo=>1, bar=>2, flag=>'one'} and for the second: {foo=>2, flag=>'two'}.

Subcommands can also be a coderef, for dynamic list of subcommands. The coderef will be called as a method with hash arguments. It can be called in two cases. First, if called without argument name (usually when doing --subcommands) it must return a hashref of subcommand specifications. If called with argument name it must return subcommand specification for subcommand with the requested name only.

default_subcommand => NAME

If set, subcommand will always be set to this instead of from the first argument. To use other subcommands, you will have to use --cmd option.

common_opts => HASH

A hash of common options, which are command-line options that are not associated with any subcommand. Each option is itself a specification hash containing these keys:

  • category (str)

    Optional, for grouping options in help/usage message, defaults to Common options.

  • getopt (str)

    Required, for Getopt::Long specification.

  • handler (code)

    Required, for Getopt::Long specification.

  • usage (str)

    Optional, displayed in usage line in help/usage text.

  • summary (str)

    Optional, displayed in description of the option in help/usage text.

  • show_in_usage (bool or code, default: 1)

    A flag, can be set to 0 if we want to skip showing this option in usage in --help, to save some space. The default is to show all, except --subcommand when we are executing a subcommand (obviously).

  • show_in_options (bool or code, default: 1)

    A flag, can be set to 0 if we want to skip showing this option in options in --help. The default is to 0 for --help and --version in compact help. Or --subcommands, if we are executing a subcommand (obviously).

  • order (int)

    Optional, for ordering. Lower number means higher precedence, defaults to 1.

A partial example from the default set by the framework:

     help => {
         category        => 'Common options',
         getopt          => 'help|h|?',
         usage           => '--help (or -h, -?)',
         handler         => sub { ... },
         order           => 0,
         show_in_options => sub { $ENV{VERBOSE} },
     format => {
         category    => 'Common options',
         getopt      => 'format=s',
         summary     => 'Choose output format, e.g. json, text',
         handler     => sub { ... },
     undo => {
         category => 'Undo options',
         getopt   => 'undo',

The default contains: help (getopt help|h|?), version (getopt version|v), action (getopt action), format (getopt format=s), format_options (getopt format-options=s), json*, yaml*, perl*. If there are more than one subcommands, this will also be added: list (getopt list|l). If dry-run is supported by function, there will also be: dry_run (getopt dry-run). If undo is turned on, there will also be: undo (getopt undo), redo (getopt redo), history (getopt history), clear_history (getopt clear-history).

*) Currently only added if you say use Perinci::CmdLine 1.04.

Sometimes you do not want some options, e.g. to remove format and format_options:

 delete $cmd->common_opts->{format};
 delete $cmd->common_opts->{format_options};

Sometimes you want to rename some command-line options, e.g. to change version to use capital -V instead of -v:

 $cmd->common_opts->{version}{getopt} = 'version|V';

Sometimes you want to add subcommands as common options instead. For example:

 $cmd->common_opts->{halt} = {
     category    => 'Server options',
     getopt      => 'halt',
     summary     => 'Halt the server',
     handler     => sub {
         $cmd->{_selected_subcommand} = 'shutdown';

This will make:

 % cmd --halt

equivalent to executing the 'shutdown' subcommand:

 % cmd shutdown

exit => BOOL (default 1)

If set to 0, instead of exiting with exit(), run() will return the exit code instead.

log_any_app => BOOL (default: 1)

Whether to load Log::Any::App (enable logging output) by default. See "LOGGING" for more details.

custom_completer => CODEREF

Will be passed to Perinci::Sub::Complete's shell_complete_arg(). See its documentation for more details.

custom_arg_completer => CODEREF | {ARGNAME=>CODEREF, ...}

Will be passed to Perinci::Sub::Complete's shell_complete_arg(). See its documentation for more details.

pass_cmdline_object => BOOL (optional, default 0)

Whether to pass special argument -cmdline containing the Perinci::CmdLine object to function. This can be overriden using the pass_cmdline_object on a per-subcommand basis.

Passing the cmdline object can be useful, e.g. to call run_help(), etc.

pa_args => HASH

Arguments to pass to Perinci::Access. This is useful for passing e.g. HTTP basic authentication to Riap client (Perinci::Access::HTTP::Client):

 pa_args => {handler_args => {user=>$USER, password=>$PASS}}

undo => BOOL (optional, default 0)

Whether to enable undo/redo functionality. Some things to note if you intend to use undo:

  • These common command-line options will be recognized

    --undo, --redo, --history, --clear-history.

  • Transactions will be used

    use_tx=>1 will be passed to Perinci::Access, which will cause it to initialize the transaction manager. Riap requests begin_tx and commit_tx will enclose the call request to function.

  • Called function will need to support transaction and undo

    Function which does not meet qualifications will refuse to be called.

    Exception is when subcommand is specified with undo=>0, where transaction will not be used for that subcommand. For an example of disabling transaction for some subcommands, see bin/u-trash in the distribution.

undo_dir => STR (optional, default ~/.<program_name>/.undo)

Where to put undo data. This is actually the transaction manager's data dir.


new(%opts) => OBJ

Create an instance.

run() -> INT

The main routine. Its job is to parse command-line options in @ARGV and determine which action method (e.g. run_call(), run_help(), etc) to run. Action method should return an integer containing exit code. If action method returns undef, the next action candidate method will be tried.

After that, exit() will be called with the exit code from the action method (or, if exit attribute is set to false, routine will return with exit code instead).


This module observes the following Rinci metadata property attributes:

x.perinci.cmdline.default_format => STR

Set default output format (if user does not specify via --format command-line option).


This module interprets the following result metadata property/attribute:

property: is_stream => BOOL

XXX should perhaps be defined as standard in Rinci::function.

If set to 1, signify that result is a stream. Result must be a glob, or an object that responds to getline() and eof() (like a Perl IO::Handle object), or an array/tied array. Format must currently be text (streaming YAML might be supported in the future). Items of result will be displayed to output as soon as it is retrieved, and unlike non-streams, it can be infinite.

An example function:

 $SPEC{cat_file} = { ... };
 sub cat_file {
     my %args = @_;
     open my($fh), "<", $args{path} or return [500, "Can't open file: $!"];
     [200, "OK", $fh, {is_stream=>1}];

another example:

 use Tie::Simple;
 $SPEC{uc_file} = { ... };
 sub uc_file {
     my %args = @_;
     open my($fh), "<", $args{path} or return [500, "Can't open file: $!"];
     my @ary;
     tie @ary, "Tie::Simple", undef,
         SHIFT     => sub { eof($fh) ? undef : uc(~~<$fh> // "") },
         FETCHSIZE => sub { eof($fh) ? 0 : 1 };
     [200, "OK", \@ary, {is_stream=>1}];

See also Data::Unixish and App::dux which deals with streams.

attribute: cmdline.display_result => BOOL

If you don't want to display function output (for example, function output is a detailed data structure which might not be important for end users), you can set cmdline.display_result result metadata to false. Example:

 $SPEC{foo} = { ... };
 sub foo {
     [200, "OK", $data, {"cmdline.display_result"=>0}];

attribute: cmdline.page_result => BOOL

If you want to filter the result through pager (currently defaults to $ENV{PAGER} or less -FRSX), you can set cmdline.page_result in result metadata to true.

For example:

 $SPEC{doc} = { ... };
 sub doc {
     [200, "OK", $doc, {"cmdline.page_result"=>1}];

attribute: cmdline.pager => STR

Instruct Perinci::CmdLine to use specified pager instead of $ENV{PAGER} or the default less or more.

attribute: cmdline.exit_code => INT

Instruct Perinci::CmdLine to use this exit code, instead of using (function status - 300).



    Can be used to set CLI program name.


    Can be used to set color_theme.


    Explicitly turn the progress bar on/off.

  • PAGER => STR

    Like in other programs, can be set to select the pager program (when cmdline.page_result result metadata is active). Can also be set to '' or 0 to explicitly disable paging even though cmd.page_result result metadata is active.

  • COLOR => INT

    Please see SHARYANTO::Role::TermAttrs.

  • UTF8 => BOOL

    Please see SHARYANTO::Role::TermAttrs.


How do I debug my program?

You can set environment DEBUG=1 or TRACE=1. See Log::Any::App for more details.

How does Perinci::CmdLine compare with other CLI-app frameworks?

The main difference is that Perinci::CmdLine accesses your code through Riap protocol, not directly. This means that aside from local Perl code, Perinci::CmdLine can also provide CLI for code in remote hosts/languages. For a very rough demo, download and run this PHP Riap::TCP server on your system. After that, try running:

 % peri-run riap+tcp://localhost:9090/terbilang --help
 % peri-run riap+tcp://localhost:9090/terbilang 1234

Everything from help message, calling, argument checking, tab completion works for remote code as well as local Perl code.

How to add support for new output format (e.g. XML, HTML)?

See Perinci::Result::Format.

My function has argument named 'format', but it is blocked by common option '--format'!

To add/remove/rename common options, see the documentation on common_opts attribute. In this case, you want:

 delete $cmd->common_opts->{format};
 #delete $cmd->common_opts->{format_options}; # you might also want this

or perhaps rename it:

 $cmd->common_opts->{output_format} = $cmd->common_opts->{format};
 delete $cmd->common_opts->{format};

How to accept input from STDIN (or files)?

If you specify 'cmdline_src' to 'stdin' to a 'str' argument, the argument's value will be retrieved from standard input if not specified. Example:

 use Perinci::CmdLine;
 $SPEC{cmd} = {
     v => 1.1,
     args => {
         arg => {
             schema => 'str*',
             cmdline_src => 'stdin',
 sub cmd {
     my %args = @_;
     [200, "OK", "arg is '$args{arg}'"];

When run from command line:

 % cat file.txt
 This is content of file.txt
 % cat file.txt | cmd
 arg is 'This is content of file.txt'

If your function argument is an array, array of lines will be provided to your function. A mechanism to be will be provided in the future (currently not yet specified in Rinci::function specification).

But I don't want the whole file content slurped into string/array, I want streaming!

If your function argument is of type stream or filehandle, an I/O handle will be provided to your function instead. But this part is not implemented yet.

Currently, see App::dux for an example on how to accomplish this on function argument of type array. Basically in App::dux, you feed an array tied with Tie::Diamond as a function argument. Thus you can get lines from file/STDIN iteratively with each().

My function has some cmdline_aliases or cmdline_src defined but I want to change it!

For example, your f1 function metadata might look like this:

 package Package::F1;
 our %SPEC;
 $SPEC{f1} = {
     v => 1.1,
     args => {
         foo => {
             cmdline_aliases => { f=> {} },
         bar => { ... },
         fee => { ... },
 sub f1 { ... }

And your command-line script f1:

 use Perinci::CmdLine;
 Perinci::CmdLine->new(url => '/Package/F1/f1')->run;

Now you want to create a command-line script interface for this function, but with -f as an alias for --fee instead of --foo. This is best done by modifying the metadata and creating a wrapper function to do this, e.g. your command-line script f1 becomes:

 package main;
 use Perinci::CmdLine;
 use Package::F1;
 use Data::Clone;
 our %SPEC;
 $SPEC{f1} = clone $Package::F1::SPEC{f1};
 delete $SPEC{f1}{args}{foo}{cmdline_aliases};
 $SPEC{f1}{args}{fee}{cmdline_aliases} = {f=>{}};
 *f1 = \&Package::F1::f1;
 Perinci::CmdLine->new(url => '/main/f1')->run;

This also demonstrates the convenience of having the metadata as a data structure: you can manipulate it however you want.

How to do custom completion for my argument?

By default, Perinci::Sub::Complete's complete_arg_val() can employ some heuristics to complete argument values, e.g. from the in clause or max and min:

 $SPEC{set_ticket_status} = {
     v => 1.1,
     args => {
         ticket_id => { ... },
         status => {
             schema => ['str*', in => [qw/new open stalled resolved rejected/],

But if you want to supply custom completion, the Rinci::function specification allows specifying a completion property for your argument, for example:

 use Perinci::Sub::Complete qw(complete_array);
 $SPEC{del_user} = {
     v => 1.1,
     args => {
         username => {
             schema => 'str*',
             req => 1,
             pos => 0,
             completion => sub {
                 my %args = @_;

                 # get list of users from database or whatever
                 my @users = ...;
                 complete_array(array=>\@users, word=>$args{word});

You can use completion your command-line program:

 % del-user --username <tab>
 % del-user <tab> ; # since the 'username' argument has pos=0

My custom completion does not work, how do I debug it?

Completion works by the shell invoking our (the same) program with COMP_LINE and COMP_POINT environment variables. You can do something like this to see debugging information:

 % COMP_LINE='myprog --arg x' COMP_POINT=13 PERL5OPT=-MLog::Any::App TRACE=1 myprog --arg x

My application is OO?

This framework is currently non-OO and function-centric. There are already several OO-based command-line frameworks on CPAN.


cmdline_src argument specification has not been fully implemented: Providing I/O handle for argument of type stream/filehandle.


Perinci, Rinci, Riap.

Other CPAN modules to write command-line applications: App::Cmd, App::Rad, MooseX::Getopt.


Please visit the project's homepage at


Source repository is at


Please report any bugs or feature requests on the bugtracker website

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


Steven Haryanto <>


This software is copyright (c) 2014 by Steven Haryanto.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.