NAME
Data::CSel - Select tree node objects using CSS Selector-like syntax
VERSION
This document describes version 0.128 of Data::CSel (from Perl
distribution Data-CSel), released on 2022-06-07.
SYNOPSIS
use Data::CSel qw(csel csel_each);
# using csel():
my @cells = csel("Table[name=~/data/i] TCell[value != '']:first", $tree);
for (@cells) { say $_->value }
# using csel_each():
csel_each { say $_->value } "Table[name=~/data/i] TCell[value != '']:first", $tree;
Using selection object:
# ditto, but wrap result using a Data::CSel::Selection
my $res = csel({wrap=>1}, "Table ...", $tree);
# call method 'foo' of each node object (works even when there are zero nodes
# in the selection object, or when some nodes do not support the 'foo' method
$res->foo;
DESCRIPTION
This module lets you use a query language (hereby named CSel) that is
similar to CSS Selector to select nodes from a tree of objects.
EXPRESSION SYNTAX
The following is description of the CSel query expression. It is modeled
after the CSS Selector syntax with some modification (see "Differences
with CSS selector").
An *expression* is a chain of one or more selectors separated by commas.
A *selector* is a chain of one or more simple selectors separated by
combinators.
A *combinator* is either: whitespace (descendant combinator), ">" (child
combinator), "~" (general sibling combinator), or "+" (adjacent sibling
combinator). "E F", or two elements combined using descendant
combinator, means F element descendant of an E element. "E > F" means F
element child of E element. "E ~ F" means F element preceded by an E
element. "E + F" means F element immediately preceded by an E element.
A *simple selector* is either a type selector (see "Type selector") or
universal selector (see "Universal selector") followed immediately by
zero or more attribute selectors (see "Attribute selector" or class
selector (see "Class selector"" in ") or ID selector (see "ID selector")
or pseudo-classes (see "Pseudo-class"" in "), in any order. Type or
universal selector is optional if there is at least one attribute
selector or pseudo-class.
Type selector
A *type selector* is a Perl class/package name.
Example:
My::Class
will match any "My::Class" object. Subclasses of "My::Class" will *not*
be matched, use class selector for that.
Universal selector
A *universal selector* is "*" and matches any class/package.
Example:
*
will match any object.
Attribute selector
An *attribute selector* filters objects based on the value of their
attributes. The syntax is:
[ATTR]
[ATTR OP LITERAL]
"[ATTR]" means to only select objects that have an attribute named
"ATTR", for example:
[length]
means to select objects that respond to ("can()") "length()".
Note: to select objects that do not have a specified attribute, you can
use the ":not" pseudo-class (see "Pseudo-class"), for example:
:not([length])
"[ATTR OP LITERAL]" means to only select objects that have an attribute
named "ATTR" that has value that matches the expression specified by
operator "OP" and operand "LITERAL". For example:
[length > 12]
[is_done is true]
[name =~ /foo/]
Calling methods "ATTR" can also be replaced by "METH()" or
"METH(LITERAL, ...)" to allow passing arguments to methods. Note that
this specific syntax:
[METH()]
does not simply mean to select objects that respond to "METH", but
actually:
[METH() is true]
For example:
# select objects that have non-zero length
[length()]
# while this means to select objects that have 'length' attribute
[length]
# select objects for which the method call returns true
[has_key('foo')]
Experimental: a chain of attributes is allowed for the attribute, for
example:
[date.month = 12]
will select only objects that has an attribute "date", and the value of
"date" is an object that has an attribute "month", and the value of
"month" is 12. When there is a failure in the chain somewhere (e.g. the
"date" object does not have the "month" attribute), the whole expression
evaluates to false.
Literal
There are several kinds of literals supported.
Numbers. Examples:
1
-2.3
4.5e-6
Boolean:
true
false
Null (undef):
null
String. Either single-quoted (only recognizes the escape sequences "\\"
and "\'"):
'this is a string'
'this isn\'t hard'
or double-quoted (currently recognizes the escape sequences "\\", "\"",
"\'", "\$" [literal $], "\t" [tab character], "\n" [newline], "\r"
[linefeed], "\f" [formfeed], "\b" [backspace], "\a" [bell], "\e"
[escape], "\0" [null], octal escape e.g. "\033", hexadecimal escape e.g.
"\x1b"):
"This is a string"
"This isn't hard"
"Line 1\nLine 2"
For convenience, a word string can be unquoted in expression, e.g.:
[name = ujang]
is equivalent to:
[name = 'ujang']
Regex literal. Must be delimited by "/.../" or "qr(...)", can be
followed by zero of more regex modifier characters m, s, i):
//
/ab(c|d)/i
qr(foo/bar)
Array. Examples:
[]
[1,2,3]
["foo", "bar","baz"]
Operators
The following are supported operators:
* "eq"
String equality using Perl's "eq" operator.
Example:
Table[title eq "TOC"]
selects all "Table" objects that have "title()" with the value of
"TOC".
* "=" (or "==")
Numerical equality using Perl's "==" operator.
Example:
TableCell[length=3]
selects all "TableCell" objects that have "length()" with the value
of 3.
To avoid common trap, will switch to using Perl's "eq" operator when
operand does not look like number, e.g.:
Table[title = 'foo']
is the same as:
Table[title eq 'foo']
* "ne"
String inequality using Perl's "ne" operator.
Example:
Table[title ne "TOC"]
selects all "Table" objects that have "title()" with the value not
equal to "TOC".
* "!=" (or "<>")
Numerical inequality using Perl's "!=" operator.
Example:
TableCell[length != 3]
TableCell[length <> 3]
selects all "TableCell" objects that have "length()" with the value
not equal to 3.
To avoid common trap, will switch to using Perl's "ne" operator when
operand does not look like number, e.g.:
Table[title != 'foo']
is the same as:
Table[title ne 'foo']
* "gt"
String greater-than using Perl's "gt" operator.
Example:
Person[first_name gt "Albert"]
selects all "Person" objects that have "first_name()" with the value
asciibetically greater than "Albert".
* ">"
Numerical greater-than using Perl's ">" operator.
Example:
TableCell[length > 3]
selects all "TableCell" objects that have "length()" with the value
greater than 3.
To avoid common trap, will switch to using Perl's "gt" operator when
operand does not look like number, e.g.:
Person[first_name > 'Albert']
is the same as:
Person[first_name gt "Albert"]
* "ge"
String greater-than-or-equal-to using Perl's "ge" operator.
Example:
Person[first_name ge "Albert"]
selects all "Person" objects that have "first_name()" with the value
asciibetically greater than or equal to "Albert".
* ">="
Numerical greater-than-or-equal-to using Perl's ">=" operator.
Example:
TableCell[length >= 3]
selects all "TableCell" objects that have "length()" with the value
greater than or equal to 3.
To avoid common trap, will switch to using Perl's "ge" operator when
operand does not look like number, e.g.:
Person[first_name >= 'Albert']
is the same as:
Person[first_name ge "Albert"]
* "lt"
String less-than using Perl's "lt" operator.
Example:
Person[first_name lt "Albert"]
selects all "Person" objects that have "first_name()" with the value
asciibetically less than "Albert".
* "<"
Numerical less-than using Perl's "<" operator.
Example:
TableCell[length < 3]
selects all "TableCell" objects that have "length()" with the value
less than 3.
To avoid common trap, will switch to using Perl's "lt" operator when
operand does not look like number, e.g.:
Person[first_name < 'Albert']
is the same as:
Person[first_name lt "Albert"]
* "le"
String less-than-or-equal-to using Perl's "le" operator.
Example:
Person[first_name le "Albert"]
selects all "Person" objects that have "first_name()" with the value
asciibetically less than or equal to "Albert".
* "<="
Numerical less-than-or-equal-to using Perl's "<=" operator.
Example:
TableCell[length <= 3]
selects all "TableCell" objects that have "length()" with the value
less than or equal to 3.
To avoid common trap, will switch to using Perl's "le" operator when
operand does not look like number, e.g.:
Person[first_name <= 'Albert']
is the same as:
Person[first_name le "Albert"]
* "=~" and "!~"
Filter only objects where the attribute named *attr* has the value
matching regular expression *value*. Operand should be a regex
literal. Regex literal must be delimited by "/.../" or "qr(...)".
Example:
Person[first_name =~ /^Al/]
selects all "Person" objects that have "first_name()" with the value
matching the regex "/^Al/".
Person[first_name =~ qr(^al)i]
Same as previous example except the regex is case-insensitive.
"!~" is the opposite of "=~", just like in Perl. It checks whether
*attr* has value that does not match regular expression.
* "is" and "isnt"
Testing truth value or definedness. Value can be null or boolean
literal.
Example:
DateTime[is_leap_year is true]
will select all DateTime objects where its "is_leap_year" attribute
has a true value.
DateTime[is_leap_year is false]
will select all DateTime objects where its "is_leap_year" attribute
has a false value.
Person[age isnt null]
will select all Person objects where age is defined.
* "has" and "hasnt"
Attribute value must be array. Will evaluate to true if one of the
elements matches the operand.
Examples:
Headline[tags has "tag1"]
Headline[tags has "tag2"][tags has "tag3"][tags hasnt "tag4"]
* "in" and "notin"
Operand must be array. Will evaluate to true if one of the elements
of array matches the attribute value.
Examples:
Headline[level in [1,2,3]]
Headline[level not in [1,2]][tags notin ["old","deprecated"]]
Class selector
A *class selector* is a "." (dot) followed by Perl class/package name.
.CLASSNAME
It selects all objects that "isa()" a certain class. The difference with
type selector is that inheritance is observed. So:
.My::Class
will match instances of "My::Class" as well as subclasses of it.
ID selector
An *ID selector* is a "#" (hash) followed by an identifier:
#ID
It is a special/shortcut form of attribute selector where the attribute
is "id" and the operator is "=":
[id = ID]
The "csel()" function allows you to configure which attribute to use as
the ID attribute, the default is "id".
Pseudo-class
A *pseudo-class* is ":" (colon) followed by pseudo-class name (a
dash-separated word list), and optionally a list of arguments enclosed
in parentheses.
:PSEUDOCLASSNAME
:PSEUDOCLASSNAME(ARG, ...)
It filters result set based on some criteria. Currently supported
pseudo-classes include:
* ":first"
Select only the first object from the result set.
Example:
Person[name =~ /^a/i]:first
selects the first person whose name starts with the letter "A".
* ":last"
Select only the last item from the result set.
Example:
Person[name =~ /^a/i]:last
selects the last person whose name starts with the letter "A".
* ":first-child"
Select only objects that are the first child of their parent.
* ":last-child"
Select only objects that are the last child of their parent.
* ":only-child"
Select only objects that is the only child of their parent.
* ":nth-child(n)"
Select only objects that are the *n*th child of their parent.
* ":nth-last-child(n)"
Select only objects that are the *n*th last child of their parent.
* ":first-of-type"
Select only objects that are the first child of their parent of
their type. So if a parent's children is:
id1(type=T1) id2(T2) id3(T2)
then both "id1" and "id2" are first children of their respective
types.
* ":last-of-type"
Select only objects that are the last child of their parent of their
type.
* ":only-of-type"
Select only objects that are the only child of their parent of their
type.
* ":nth-of-type(n)"
Select only objects that are the *n*th child of their parent of
their type.
* ":nth-last-of-type(n)"
Select only objects that are the *n*th last child of their parent of
their type.
* ":root"
Select only root node(s).
* ":has-min-children(m)"
Select only objects that have at least *m* direct children.
* ":has-max-children(n)"
Select only objects that have at most *n* direct children.
* ":has-children-between(m,n)"
Select only objects that have between *m* and *n* direct children.
* ":parent"
Select the node's parent.
* ":empty"
Select only leaf node(s).
See also ":has".
* :not(S)
Select all objects not matching selector "S". "S" can be a string or
an unquoted CSel expression.
Example:
:not('.My::Class')
:not(.My::Class)
will select all objects that are not of "My::Class" type.
* :has(S)
Select all objects that have a descendant matching selector "S". "S"
can be a string or an unquoted CSel expression.
Example:
:has('T')
:not(T)
will select all objects that have a descendant of type "T".
See also: ":parent".
Differences with CSS selector
Type selector can contain double colon ("::")
Since Perl package names are separated by "::", CSel allows it in type
selector.
Syntax of attribute selector is a bit different
In CSel, the syntax of attribute selector is made simpler and more
regular.
There are operators not supported by CSel, but CSel adds more operators
from Perl. In particular, the whole substring matching operations like
"[attr^=val]", "[attr$=val]", "[attr*=val]", "[attr~=val]", and
"[attr|=val]" are replaced with the more flexible regex matching instead
"[attr =~ /re/]".
Different pseudo-classes supported
Some CSS pseudo-classes only make sense for a DOM or a visual browser,
e.g. ":link", ":visited", ":hover", so they are not supported.
CSS selector does not sport ":parent".
There is no concept of CSS namespaces
CSS namespaces are used when there are foreign elements (e.g. SVG in
addition to HTML) and one wants to use the same stylesheet for both.
There is no need for something like this CSel, as we deal with only Perl
objects.
VARIABLES
@Data::CSel::CLASS_PREFIXES
Array of namespace prefixes to check when matching type in type selector
as well as class selector. This is like PATH environment variable in
Unix shell. For example, if @CLASS_PREFIXES is "["Foo::Bar", "Baz"]",
then this expression:
T
will match class "Foo::Bar::T", or "Baz::T", or "T".
Note that @Data::CSel::CLASS_PREFIXES is consulted after the
"class_prefixes" opton in "csel()".
FUNCTIONS
csel
Usage:
$list_or_selection_obj = csel([ \%opts , ] $expr, @tree_nodes)
Select from tree node objects @tree_nodes using CSel expression $expr.
Will return a list of mattching node objects (unless when "wrap" option
is true, in which case will return a Data::CSel::Selection object
instead). Will die on errors (e.g. syntax error in expression, objects
not having the required methods, etc).
A tree node object is any regular Perl object satisfying the following
criteria: 1) it supports a "parent" method which should return a single
parent node object, or undef if object is the root node); 2) it supports
a "children" method which should return a list (or an arrayref) of
children node objects (where the list/array will be empty for a leaf
node). Note: you can use Role::TinyCommons::Tree::Node to enforce this
requirement. Note: the "parent" and "children" method names can actually
be customized, see options.
Known options:
* class_prefixes => array of str
Array of namespace prefixes to check when matching type in type
selector as well as class selector. This is like PATH environment
variable in Unix shell. For example, if "class_prefixes" is
"["Foo::Bar", "Baz"]", then this expression:
T
will match class "Foo::Bar::T", or "Baz::T", or "T".
Note that @Data::CSel::CLASS_PREFIXES is also consulted after this
"class_prefixes" option.
* wrap => bool
If set to true, instead of returning a list of matching nodes, the
function will return a Data::CSel::Selection object instead (which
wraps the result, for convenience). See the selection object's
documentation for more details.
* get_parent_method => str
Example:
get_parent_method => 'get_parent'
This option can be used if your node object uses method other than
the default "parent" to get parent node.
* set_parent_method => str
Example:
set_parent_method => 'set_parent'
This option can be used if your node object uses method other than
the default "parent" to set parent node.
* get_children_method => str
Example:
get_children_method => 'get_children'
This option can be used if your node object uses method other than
the default "children" to get children nodes.
* set_children_method => str
Example:
set_children_method => 'set_children'
This option can be used if your node object uses method other than
the default "children" to set children nodes.
csel_each
Usage:
csel_each { say $_[0]->value } "expr", $tree;
csel_each { say $_->value } {csel_opt1=>..., ...}, "expr", $tree1, $tree2;
Execute callback for every node that matches expression. Basically
shortcut for:
my @nodes = csel(...);
for (@nodes) { $callback->($_) )}
The callback will retrieve the node either in the first element of @_ or
in the localized $_ for convenience.
parse_csel
Usage:
$hash = parse_csel($expr);
Parse an expression. On success, will return a hash containing parsed
information. On failure, will return undef.
FAQ
Can I use csel() against a regular data structure (instead of a tree of objects)?
Use Data::CSel::WrapStruct to create a tree of object from the data
structure, then perform "csel()" on the resulting tree.
HOMEPAGE
Please visit the project's homepage at
<https://metacpan.org/release/Data-CSel>.
SOURCE
Source repository is at <https://github.com/perlancar/perl-Data-CSel>.
SEE ALSO
Related to CSS selector
CSS4 Selectors Specification, <https://www.w3.org/TR/selectors4/>.
These modules let you use CSS selector syntax (or its subset) to select
nodes of an HTML document: Mojo::DOM (or DOM::Tiny), jQuery, pQuery,
HTML::Selector::XPath (or via Web::Query). The last two modules can also
handle XPath expression.
CLI to select HTML elements using CSS selector syntax: html-css-sel
(from App::html::css::sel).
Similar query languages
These modules let you use XPath (or XPath-like) syntax to select nodes
of a data structure: Data::DPath. Like CSS selectors, XPath is another
query language to select nodes of a document. XPath specification:
<https://www.w3.org/TR/xpath/>.
These modules let you use JSONPath syntax to select nodes of a data
structure: JSON::Path. JSONPath is a query language to select nodes of a
JSON document (data structure). JSONPath specification:
<http://goessner.net/articles/JsonPath>.
Related modules
Data::CSel::WrapStruct
CSel::Examples
Modules that use CSel
* For data structure
CLI to select JSON nodes using CSel: jsonsel (from App::jsonsel).
CLI to select Perl data structure elements using CSel: ddsel (from
App::CSelUtils).
CLI to select YAML nodes using CSel: yamlsel (from App::yamlsel).
* For HTML document
htmlsel (from App::htmlsel).
* For Org document
orgsel (from App::orgsel).
* For POD document
CLI to select POD::Elemental nodes using CSel: podsel (from
App::podsel).
* For PPI (Perl source code tree representation) document
CLI to select PPI nodes using CSel: ppisel (from App::ppisel).
AUTHOR
perlancar <perlancar@cpan.org>
CONTRIBUTING
To contribute, you can send patches by email/via RT, or send pull
requests on GitHub.
Most of the time, you don't need to build the distribution yourself. You
can simply modify the code, then test via:
% prove -l
If you want to build the distribution (e.g. to try to install it locally
on your system), you can install Dist::Zilla,
Dist::Zilla::PluginBundle::Author::PERLANCAR, and sometimes one or two
other Dist::Zilla plugin and/or Pod::Weaver::Plugin. Any additional
steps required beyond that are considered a bug and can be reported to
me.
COPYRIGHT AND LICENSE
This software is copyright (c) 2022, 2021, 2020, 2019, 2016 by perlancar
<perlancar@cpan.org>.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
BUGS
Please report any bugs or feature requests on the bugtracker website
<https://rt.cpan.org/Public/Dist/Display.html?Name=Data-CSel>
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.