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Perl provides three loop control keywords that all accept an optional loop label as an argument. If no label is specified, the keywords act on the innermost loop. Within nested loops, the use of labels enables control to move from an inner loop to an outer one, or out of the outer loop altogether.
Perl 5 hashes are flat: keys are strings and values are scalars. However, values may be references to arrays or other hashes, and the standard Perl 5 module Tie::RefHash enables hashes to be used with reference keys. A hash variable is marked by a % sigil, to distinguish it from scalar, array
In Perl, foreach (which is equivalent to the shorter for) can be used to traverse elements of a list. The expression which denotes the collection to loop over is evaluated in list-context and each item of the resulting list is, in turn, aliased to the loop variable. List literal example:
Originally, filehandles could only be created with package variables, using the ALL_CAPS convention to distinguish it from other variables. Perl 5.6 and newer also accept a scalar variable, which will be set (autovivified) to a reference to an anonymous filehandle, in place of a named filehandle.
In addition to support for vectorized arithmetic and relational operations, these languages also vectorize common mathematical functions such as sine. For example, if x is an array, then y = sin (x) will result in an array y whose elements are sine of the corresponding elements of the array x. Vectorized index operations are also supported.
The use of Perl variable interpolation to programmatically customize each of the SQL queries, and the specification of Perl arrays or hashes as the structures to programmatically hold the resulting data sets from each SQL query, allows a high-level mechanism for handling large amounts of data for post-processing by a Perl subprogram. [132]
Perl Data Language (abbreviated PDL) is a set of free software array programming extensions to the Perl programming language. PDL extends the data structures built into Perl, to include large multidimensional arrays , and adds functionality to manipulate those arrays as vector objects.
In Perl [2] and Raku [3] the 3-character ellipsis is also known as the "yada yada yada" operator and, similarly to its linguistic meaning, serves as a "stand-in" for code to be inserted later. Python3 also allows the 3-character ellipsis to be used as an expressive place-holder for code to be inserted later.