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In Windows PowerShell, which was partly inspired by Unix shells and Perl, variable names are prefixed by the "$" sigil. In XSLT, variables and parameters have a leading "$" sigil on use, although when defined in <xsl:param> or <xsl:variable> with the "name" attribute, the sigil is not included.
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.
Perl takes some cues from its C heritage for conventions. Locally scoped variables and subroutine names are lowercase with infix underscores. Subroutines and variables meant to be treated as private are prefixed with an underscore. Package variables are title cased. Declared constants are all caps.
Perl borrows features from other programming languages including C, sh, AWK, and sed. [1] It provides text processing facilities without the arbitrary data-length limits of many contemporary Unix command line tools. [16] Perl is a highly expressive programming language: source code for a given algorithm can be short and highly compressible. [17 ...
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 5.6.1 and newer support autovivification of file and directory handles. [3] Calling open() on an undefined variable will set it to a filehandle. According to perl561delta, "[t]his largely eliminates the need for typeglobs when opening filehandles that must be passed around, as in the following example:
Prolog, for both atoms (predicate names, function names, and constants) and variables [20] Python, for variable names, function names, method names, and module or package (i.e. file) names [3] PHP uses SCREAMING_SNAKE_CASE for class constants; PL/I [21] R, for variable names, function names, and argument names, especially in the tidyverse style ...
When a variable is pre-declared, it provides the programmer with information that he might be interested in. For example, in the Perl language, a variable %ENV is pre-declared, holding all kinds of environmental information such as the operating system, host information, user information, and many more. Other pre-declared variables in Perl are ...